RX113 Group - Renesas Electronics
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1. Count value averagin a Bing gt Interrupt Finish measurement Reference value generating Firmwa re process Drift compensation l Key judgement Figure 4 17 the timing diagram of CTSU and Firmware process b Generating the reference value and the threshold value Cap touch key is different from the mechanical switch key and there is not clear status of ON or OFF as same as the mechanical switch It is judged by the change of the counts capacitance when touch occurs The firmware maintains a long term average value of the counts which is called the reference value The reference value is compared to the last scan value and if the difference is greater than a configured delta referred to as the threshold the firmware judges key ON The reference values is updated at a specified rate to compensate for environmental changes this compensation is referred to as drift compensation The compensation rate is user configurable but is typically every 2 3 seconds The scan values are filtered by a running average filter so key response time can be changed by modifying the number of averaging and its speed Cap touch key s sensitivity can be changed by changing the threshold value Drift compensation updates are held off while a key is judged to be touched so a pressed key does not turn off due to the drift compensation setting the reference equal to the touched value Refer Figure 4 18 RO1AN2516EU0100 Ver 0 9 Page 292. ENESAS APPLICATION NOTE RX113 Group RO1AN2516EU010 Ver 0 9 Design Guide for Renesas Touch Solution Dec 1 2014 Summary The RX113 group has incorporated hardware Capacitive Touch Sensor Unit CTSU that detects human body contact by measuring capacitance existed between touch electrode and human body This application note introduces the principle of capacitive touch detection as well as explains the detail of current frequency conversion system that is used in RX113 Target Device RX113 Group Contents A o tons E E E 3 2 The Basic of Capacitive Touch SWitCH cccccccccccccccccncnnnnnnnnonnnnnnnnnononnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnneneness 3 2 1 Generation of Electrostatic Capacitar 4 22 Capacitance C urreni Conversion aaa 5 23 DIAS E U i esen E E E E coins 7 2 4 ON OFF switch judgment cccccccsseseesssseseeecseeecececececcnsceeesscsseseeseececesccccsseceeeasesssseseeeceeeceeccssececusssssseeeeeeess 7 3 The Capacitive Touch Detection System Of ReNesasS ccccccccccccccncccncncnnnnnnnnnnnnnnnnnnonononononononnnnnnnonons 9 eh a A e o o OE E O a o O O A 9 O E A e Un A A OM A seca 10 3 2 1 SA A e e O N A E N AT N AT EATE 10 3 2 2 I O Driver amp Drive pulse SEN cad 11 3 4 3 Analog Front A ee IP O EE e Pr E ER Ei a a ar aier 11 324 Dala COn Tol CPU eatceecsete nev asioise pansy essecedeenearetnsieveno in aneetedeanseatadonchautinaaradidenssnieandasdemeaacteases 13 L AR MMMM YG AG POP COMO PP 0
3. R China 200333 Tel 86 21 2226 0888 Fax 86 21 2226 0999 Renesas Electronics Hong Kong Limited Unit 1601 1613 16 F Tower 2 Grand Century Place 193 Prince Edward Road West Mongkok Kowloon Hong Kong Tel 852 2265 6688 Fax 852 2886 9022 9044 Renesas Electronics Taiwan Co Ltd 13F No 363 Fu Shing North Road Taipei 10543 Taiwan Tel 886 2 8175 9600 Fax 886 2 8175 9670 Renesas Electronics Singapore Pte Ltd 80 Bendemeer Road Unit 06 02 Hyflux Innovation Centre Singapore 339949 Tel 65 6213 0200 Fax 65 6213 0300 Renesas Electronics Malaysia Sdn Bhd Unit 906 Block B Menara Amcorp Amcorp Trade Centre No 18 Jin Persiaran Barat 46050 Petaling Jaya Selangor Darul Ehsan Malaysia Tel 60 3 7955 9390 Fax 60 3 7955 9510 Renesas Electronics Korea Co Ltd 12F 234 Teheran ro Gangnam Ku Seoul 135 920 Korea Tel 82 2 558 3737 Fax 82 2 558 5141 O 2014 Renesas Electronics Corporation All rights reserved Colophon 4 0
4. Signal wiring PWM s Ag on Top and Bottom ectrode wiring Figure 4 5 Wiring pattern e GND shield for the electrode and it s wiring A ground plane can be an effective measure against radiated and conducted noise When using a ground plane a mesh ground pattern as shown in Figure 4 6 is effective to decrease the parasitic capacitance TSCAP port It is necessary to insert 10nF capacitance between TS port and GND to act as low pass filter This capacitance must be nearby TSCAP port and the wiring must be short as possible RO1AN2516EU0100 Ver 0 9 Page 19 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 4 2 2 Design of the mutual capacitance method Cap touch key board a Outline Capacitive touch detection by the mutual method utilizes the phenomenon that a part of capacitive field coupling between the mutual electrodes is diverted to ground by a material such as a human body as shown in Figure 1 1 When using the mutual method one electrode is driven as the transmitting electrode and the other is connected to the capacitance detector as the receiving electrode The capacity detector measures the coupling of electric charge from one electrode to the other If the conductive material comes closer the mutual electrode a part of capacitive coupling is diverted into that object and the coupling to the receiving electrode is decreased By periodically measuring the coupled field it is possible to det
5. IO driver base clock cycle and measurement number are transferred by DTC SCF frequency and the measurement period are changeable for each TS port The IO driver base clock and the measurement period must be considered for each TS port individually since it is dependent on the parasitic capacitance and the resistance of each measurement port it is also important to insure the Sensor ICO counter does not overflow Figure 4 14 shows the relationship of IO driver output and ICO counter In this example it shows when CTSUSNUM resgister is set to mearue twice ICO counter count value becomes OXFFFF as the result there is an overflow and it is impossible to get a correct measurement value When ICO counter overflows the measurement value is fixed OXFFFF and CTSUSOVE Sensor ICO counter overflow flag or and CTSUROVE Reference ICO counter overflow flag are set 1 These flags musbt be cleared manually 1 Count Value Overflow OXFFFF time ICO counter time count value lO driver output A period of pulse output CTSUSNUM 0 A period of lO counter counting Counter Captures Count value CTSUSNUM 1 lt A period of IO counter counting gt Counter Captures Count value Figure 4 15 the relation example of IO driver output and ICO counter 3 Determination of lO driver frequency As it is described above IO driver frequency is a key parameter un determining the measurement sensitivity of capacitan
6. and inverts the phase Polynomial counter is controlling to randomize the phase of pulse output from Phase shifter based on the pseudorandom number and generating polynomial Output from Phase shifter is normalized by FM modulation output of ICO for spread spectrum and randomized the cycle Pulse output that was randomized for both phase and cycle is sent to I O driver and randomize the switch timing of I O Driver In this way the purpose of Drive RO1AN2516EU0100 Ver 0 9 Page 13 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution pulse generator is to spread the cycle and phase of SCF switch timing in I O Driver control the synchronization of exogenous noise and switch timing and protect the influence to touch detection The detail is described later From AFE L Tooo To I O Driver ia From CPU oscillator Polynomial Counter Figure 3 8 Drive pulse generator b Reference counter amp Sensor counter The structure of Reference counter and Sensor counter is shown in figure 3 9 These counters are controlled by Sequencer and count the pulse outputting from ICO for a certain time The count value is transferred to RAM of CPU unit through DTC The count value transferred to RAM is eventually processed by the software and be able to detect the changes of capacitance that is contact of the human body From AFE Digital control Reference ICO counter J Sensor ICO counter i Sequ
7. capacity coupling between the electrode and GND is very small and noise immunity may be degraded Over 50pF The current required to drive the capacitance is beyond CTSU design capacity Table 4 2 Table of the approximate parasitic capacitance and Sensor ICO count value Approximately 10 10201 11000 Approximately 12 11001 11900 Approximately 15 11901 13000 Approximately 18 19601 20300 20301 or over Over 50 Sensor ICO count is the actual value measured by RX113 sample chip IO driver frequency gains with using the approximate capacitance and the resistance value Table 4 3 ao i TT MEMO TIRA Te AAA mere meret E EET ESEL EDE 7 E EE T E T 51 TUR 451 u 5088 3 056 3 8 A ULA H o E gr 11700 19089 1028 278 3 MOPATE M3 18222 BEE 1924 10120 5 1490 E 17194 i ES 1 LIE 288205 20831 PORT 29826 818 Be ai ieee ee an aa ie 2970987 NTE BA 2000 20217 SOE O aoe ee tee ent ee ee pod ni A i 0 5MHz Y TO 92 09 60 72990 08 30 3 1903 ATEN Table 4 3 the relation of Sensor ICO frequency with the measured capacitance and the resistance R01AN2516EU0100 Ver 0 9 Page 26 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 4 Trimming of Sensor ICO Sensor ICO is a current oscillator and the amount of input current determines its frequency The linear specification of frequency with the input current is up to approximately 100MHz The linearity of the frequency response is l
8. e EE TE a Aaa A anane 3l ae E A e E e ro ESE O RC E 32 5 2 1 DET Correction OCC So ist 32 5 242 Countermeasure of Random Noise siciliana 32 saa CU SR e e Ea e E E O e E OA a EEEE 33 R01AN2516EU0100 Ver 0 9 Page 2 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 1 Introduction A capacitive touch switch using the capacitance generated between human body and touch electrode is widely used for home appliances AV equipment automotive and industrial equipment including smart phones An example of a product using capacitive touch is shown in Figurel 1 The surface is covered with a uniform plastic and there is no projections or cutouts in the design The switch is defined by characters which are highlighted using LED backlighting The touch switch is robust as there are no mechanical parts and it is much simpler than mounting a physical switch into the curved surfaces The touch technology also allows detection of finger movement so sliders wheels and simple keypads can be implemented This is difficult to achieve by the conventional switch Figure 1 1 Product example of capacitive touch switch This application note introduces the basis of capacitive touch the detail of capacitive touch switch detection of Renesas original system and examples of capacitive touch switch with our system 2 The Basic of Capacitive Touch Switch The capacitive touch switch is different from the popular switch that has the
9. electrical contact since it detects the status of the switch ON or OFF by measuring a small capacitive 1pF or less change created when the human body comes close to the electrode There are several ways to measure the capacitance and convert it to the status of switch The easiest way is called a relaxation oscillation method which forms a low pass filter LPF using capacitance and resistance When the human body changes the capacitance there is a change in timing of the LPF This method is widely used because the circuit is simple and the special capacitance measurement circuit is not necessary However it is vulnerable to noise in general and can be affected by invertor noise generated from appliances and lighting equipment The capacitive touch detection method which Renesas has developed adopts the switched capacitor filter in order to achieve both high sensitivity and noise immunity The method determines the status of switch by converting the capacitance to current amplifying and digitizing Figure 2 1 2 2 Capacitance 2 3 Digitalization 2 4 Judge the Notify the current conversion of current status of switch gt status of switch 2 1 Generation of Capacitance Figure 2 1 Flow of capacitance touch switch detection number number is the chapter number The basic of capacitance touch switch detection is described in this chapter in accordance with the flow of Figure 2 1 RO1AN2516EU0100 Ver 0 9 Page 3 of 4 Dec 1 2014 RE
10. o o a A 15 3 3 1 OVEN e o E A E A AE 15 A EE RS E E E A 15 Be IV IN a AC e E sean ncconeces oatten AE A A 5 AA 15 EINE ahaa esha PS PO O EE e O POCO E e UE UE 15 ee E E E OE 6 PO A 16 4 Designing a Touch Board and SySteM ooonccnnnnccccoccnnnccnnncccnnnnnnncnnnnnonononnnnnnnnnnnnonnnannnnnnnnnonnnananenons 16 A E E e e neo 16 Ll Desin of Cap touch DOIG atracar oriol iii laca 16 4 2 1 Design of the self capacitance method Cap touch key board ooooooonnnnncncnnnnnnnnnnnnononnnnnnannnnnnnnnnnnnnnnoss 16 RO1AN2516EU0100 Ver 0 9 Page 1 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 4 2 2 Design of the mutual capacitance method Cap touch key board oooooonnnnnccnncnncncncnnnnononononnnncnnnnnnnnnnnnos 20 Bre CES ESE SIN irte eeneonence 23 4 3 1 CTSU register setting for self capacitance Method ooocccncccccccnncnnoonnonnnnncnnnnnnnnnnnnnonononnnnnnnnnnnnnnnncnnnnnnnnnos 23 43 2 CTSU register setting for mutual capacitance Method occccccccnnnonononooonnnnnnnnnnnnnnononononnnnnnonannnnnnnnnnnnnnnos 29 E A AP o A E EE 29 4 4 1 Firmware process of self capacitance Method cccccccesseeseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 29 Be NOSE MMU eeren PPP re e GUE UU O OA 30 O OVI W eo E A UA e O 008 UE E E E 30 3 4 Noise Mala on the Board ai ae aii 31 AO or A FS e PR UE A 31 Sra Touch Electrode and W100 Oech in ncatecnedshepmdvescssaced al damoncuctnoaih a e a
11. of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution Measurement value Threshold value Reference value Touch OFF Touch ON Touch OFF Time Figure 4 18 Measurement value Reference value and Threshold value c Tuning of the firmware parameters Tuning parameters of the standard firmware are shown below Continual touch limiter There is a possibility that the key status of ON never changes due to injecting noise or the very sudden change in the parasitic capacitance The drift correction process can not follow these fast phenomenon and once the condition occurs drift compensation is disabled To return the normal status if the key ON period exceeds a configurable time that key is turned OFF and the drift correction process can correct for the condition This feature is called Continual touch limiter User can change the following parameters Continual touch limiter process ON or OFF Drift correction Multi touch cancel Response delay time to touch non touch Hysteresis Threshold 5 Noise Immunity 5 1 Overview Capacitive touch switches need to be designed so they are not affected adversely by noise or power supply variation which can result in changes to the count readings In addition to various types of noise immunity mechanisms incorporated in CTSU software filters are used in the Renesas capacitive touch solution High noise immunity should also be a ke
12. operating supply voltage range movement power voltage range heat radiation characteristics installation and other product characteristics Renesas Electronics shall have no liability for malfunctions or damages arising out of the use of Renesas Electronics products beyond such specified ranges 7 Although Renesas Electronics endeavors to improve the quality and reliability of its products semiconductor products have specific characteristics such as the occurrence of failure at a certain rate and malfunctions under certain use conditions Further Renesas Electronics products are not subject to radiation resistance design Please be sure to implement safety measures to guard them against the possibility of physical injury and injury or damage caused by fire in the event of the failure of a Renesas Electronics product such as safety design for hardware and software including but not limited to redundancy fire control and malfunction prevention appropriate treatment for aging degradation or any other appropriate measures Because the evaluation of microcomputer software alone is very difficult please evaluate the safety of the final products or systems manufactured by you 8 Please contact a Renesas Electronics sales office for details as to environmental matters such as the environmental compatibility of each Renesas Electronics product Please use Renesas Electronics products in compliance with all applicable laws and regulations that regulate the inclus
13. resistance of Rx wiring 4 3 CTSU register setting The register configuration is typically performed by the Renesas supplied firmware driver and the user does not typically need to set these registers 4 3 1 CTSU register setting for self capacitance method 1 Initialization It is necessary to set the register initial value to measure the capacitance Refer RX113 User s manual TS port setting RO1AN2516EU0100 Ver 0 9 Page 23 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution TSCAP port LPF discharge process e CTSU initialize DTC setting for transmitting and receiving from to RAM and CTSU registers 2 The explanation of the measurement time of ICO counter As discussed previously the oscillation output of Sensor ICO amp Reference ICO is counted by each Sensor CO counter amp Reference ICO counter during the measurement period and these value are stored to the registers as the count values This measurement period is set using the following register values and formula IO driver base clock cycle It is determined by PCLK frequency input to CTSU CTSU Count Source Select bit and CSTU Sensor Drive pulse Division Control bit For example PCK 32MHz CTSU Count Source Select bit PCLK 2 CTSU Sensor Drive pulse Division Control bit 1 32 The resulting IO driver base clock frequency is 0 5MHz Cycle is 2uSec The CTSU Sensor Drive pulse Division Control bit is configured for each TS port
14. 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution the same level and secondly measurement occurs when the pulse is driven to the opposite level of the SCF The Cm value is determined by subtracting the first measurement value from the secondly one The formulas below show the relationship of the currents for the two measurements These are based on the fundamental formula relating current frequency and capacitance in a switched network with a constant voltage Basic Formula Ic VFC Where Ic Capacitor Current F Switching Frequency C capacitance V Switching Voltage Mutual Capacitance Formulas Ipri FCpVd FCm Vt Vd e e eee e e e Formula 4 1 Isec FCpVd FCm Vt Vd ee eooo o e Formula 4 2 Formula 4 2 Formula 4 1 Isec Ipri FCpVd FCm Vt Vd FCpVd FCm Vt Vd 2FCmVd e e e ee o e e Formula 4 3 Ipri Primary current measurement value Isec Secondly current measurement value F Frequency of SCF and Driving pulse Vd Voltage of the pulse generator circuit Vt Voltage of SCF driving Cm Capacitance existing between the electrodes Cp Parasitic capacitance of each electrode and its wiring Formula 1 1 and Formula 1 2 show the current values resulting from the primary and secondary measurements Formula 1 4 shows the subtraction the primary measurement from the second one In the CTSU circuit F and Vd are constant values so Cm value can be calculated from F
15. Current offset value follows the sensor ICO Linearly is lost counter that is controlled as same as reference ICO count value when CTSURIOA is set O3FFh Approx 100uA Approx 20uA Current offset Approx 5uA 12000 16000 48000 64000 Sensor ICO counter output value example Sensor ICO TOURTET OULPUL ee xan Ble Characteristic Sensor ICO Input current ICO Counter offset current Characteristic Sensor ICO Input current ICO Counter Figure 4 16 the relation of Sensor ICO reference ICO and the current 5 Sensor ICO underflow If the configured offset current is greater than that required by the IO driver an underflow of Sensor ICO will occur In this situation Sensor ICO count value becomes unstable and incorrect This condition also results in an incorrect RO1AN2516EU0100 Ver 0 9 Page 28 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution TSCAP voltage and the TSCAP voltage error monitoring bit CTSUICOMP will be set When the CTSUICOMP bit is set 1 further measurements should be stopped and the offset value each TS port should be verified Hardware failures like open or shorted sensor lines can also result in the CTSUICOMP bit being set 4 3 2 CTSU register setting for mutual capacitance method a Initialize Initialization of the registers is the same as the initialization of the self capacitance method except it must also configure the which electrod
16. Guide for Renesas Touch Solution 3 The Capacitive Touch Detection System of Renesas Renesas s capacitive touch detection system has both high sensitivity and high noise immunity provided by the CTSU Capacitive Touch Sensing Unit The CTSU has analog circuitry for capacitance detection that has low impedance and high sensitivity The analog front end is coupled with an analog digital conversion circuit that achieves excellent temperature characteristic and linearity The solution includes a Capacitive touch API Application Program Interface utilizing the 32 bit CPU high speed and high efficiency that facilitates the development of capacitive touch system without user needing to fully understand operation of the hardware These hardware and software features are explained in this chapter 3 1 Overview An overview of Renesas s capacitive touch detection system is shown in figure 3 1 The system is divided into a hardware layer and a software layer The Hardware layer includes I O Driver the driver connects directly to touch electrodes and converts the capacitance to electric current created by the pulse drive Analog Front End AFE converts the electric current to frequency Digital Control controls the I O driver and AFE blocks to convert the capacitance to a digital value that is then passed to the software The Software layer includes Device Driver that controls hardware configuration and operation Middleware API tha
17. M control of LED The preferable area of the electrode 1s equal or up to twice the size of area as the point of finger contact Electrode sizes larger than twice the size of a finger can add parasitic capacitance that may lower the sensitivity Recommend Possible Not recommend Figure 4 2 the shapes of the electrode The recommended connection of the electrode to the MCU is to connect with as short a wiring as possible on the same board When those two can t be mounted on the same board due to the form of the panel alternative arrangements are shown in Figure 4 3 Panel glass acrylic etc e pr 3 gt Conductor Metallic fiber Copper aluminum foil Conductor copper aluminum foil gt Spring Flexible cable Conductor Y metal conductive rubber PCB Figure 4 3 How to connect when board and electrode are widely separated c Constructing a slider A slider can be constructed from the elements shown below The x dimensions are all consistent with the dimensioning on the first element The multiple elements are then stacked to create a slider with the desired number of elements RO1AN2516EU0100 Ver 0 9 Page 17 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 11 5 a d Electrode s wiring The wiring between the electrode and the Touchsensor TS port should be the shortest length possible It is recommended to separate the trace from nois
18. NESAS RX113 Design Guide for Renesas Touch Solution 21 Generation of Electrostatic Capacity The concept of sensing electrostatic capacity is shown in Figure 2 2 Parasitic capacity Cp exists between an electrode in the space and the conductive materials ground pattern or metal frame etc of its surroundings When a person interacts with the electrode the finger capacity Cf is generated between the human body and electrode The body acts as an additional capacitance between the electrode and ground The red line in the figure Finger Capacity Cf Electrode pid iii Conductor To detector To detector a y Parasitic Capacity Cp I I GND IIZ GND Figure 2 2 Generation of electrostatic capacity self capacitance method The resulting total capacitance is the sum of the parasitic capacitance and the finger capacitance as shown the following equation Total Capacity Cp Cf The capacitive touch switch periodically measures the total capacitance of the electrode circuit and detects the increase Cf of capacitance created by human body This detection method is referred to as the self capacitance method It consists of a single electrode The shape of electrode is also simple and circuit configuration can be implemented relatively easily However it is necessary to consider the layout and circuit configuration to reduce Parasitic Capacity as much as possible since Cf is very small and as Cp becomes la
19. OFF When this cycle repeats a certain amount of current flows intermittently synchronized with turning ON and OFF If the capacitance of the circuit is doubled while the switching frequency remains the same the current will also be doubled Figure 2 6 If the capacitance is maintained the same but the switching frequency is instead doubled the current will also double Figure 2 7 oT a I i I I I fy i 1 e i l I i Aa a e Figure 2 6 double external capacitor capacity Figure 2 7 double SW switching frequency The following equation describes the relationship between the circuit current as 1 the switch frequency as f capacitor capacity as c and circuit voltage as v i fcv In this case if f and v are constant 11s proportional toc This is the basic principle used to convert capacitance changes caused by human approach to changes of current The conversion ratio of capacitance and current can be changed by adjusting f and v RO1AN2516EU0100 Ver 0 9 Page 6 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 2 3 Digitizing of Current The capacitance which is converted to current is digitized by a circuit that changes oscillating frequency in accordance with current and a counter that counts the pulses output from the oscillator circuit The flow of digitizing process is shown in Figure 2 12 The electric current alternates because the capacitor in the SCF cha
20. The software reads the count value and processes the data to provide touch detection or position on the wheel or slider hu MCU basic voltage Regulator AFE analog front end Digital control m wo A Spread spectrum ICO Drive pulse Generator Basic current Generator VDD Sensor ICO Counter Regulator LPF CTSU Control register AN DTC CPU core Timer serial I O DTC Data Transfer Controller Driver output switch matrix Drive pulse switch matrix 7 3 Electrode Figure 3 2 overall view of hardware RO1AN2516EU0100 Ver 0 9 Page 10 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 3 2 2 I O Driver amp Drive pulse generator The structure of I O Driver is shown in figure 3 3 The I O Driver consists of a two pair of switches controlled by drive pulse supplied from the Digital Block The signal from the driver pulse generator results in the switches alternating between open and closed In accordance with previously presented equation 1 FCV the resulting current is dependent on the voltage that is supplied from Touch VDD regulator capacitance of the electrode and frequency of drive pulse This current is smoothed through LPF and sent to ICO in the Analog Front End part Touch VDD Regulator aed To AFE block Jerr mirror From Digital block JUUL Figure 3 3 diagram of l O Driver AZ Analog Front End The
21. and written to the register DTC CTsUSensor Drive pulse PCLK i Division Control bit CTSUCount Source Select bit 1 2 PCLK 1 4 i gt PCLK 2 i gt lO driver Base Clock Cycle PCLK 4 1 64 Figure 4 13 IO driver Base Clock Cycle Base pulse number This register configures the number of pulses to output from IO driver This is 1 period of IO driver output randomized by the phase shifter Measurement cycle number This is the number of times the base pulse pattern is repeated It is determined by CTSUPRRATIO register setting The Base Pulse number times the Measurement cycle number gives the number of pulses in one measurement Measurement cycle number CISU Base pulse number 1 510 2 126 62 16 Measurement number This configures the number of times a measurement is repeated on a channel before the scan is considered complete It is determined by CTSUSNUM register setting It is possible to set the measurement number to each TS port by DTC transfer Measurement time Sec IO driver base clock cycle x Base pulse number x Measurement pulse number Base pulse number 2 x 0 25 xMeasurement cycle number Formula 4 6 Measurement time RO1AN2516EU0100 Ver 0 9 Page 24 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution These values determine not only the measurement time of ICO counters but also the measurement time of each TS port The
22. ce by the CTSU If the frequency is faster than the capacitance can charge amp discharge the reading will be incorrect In addition to the capacitance that must be driven it is important to consider the resistance between the electrode and TS port since it will affect the capacitance charge amp discharge time If the resistance is already established the approximate parasitic capacitance of the cap touch key board can be measured by CTSU using the following method First the sensor ICO count value is measured by CTSU In this case CTSU register values are as follows JO driver baseclock 0 5MHz Example If PCLK 32MHz CTSUCLK 00B CTSUSDP 31 CTSUATUNEO If Vcc 2 4V then 0 else 1 RO1AN2516EU0100 Ver 0 9 Page 25 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution CTSUATINEI1 1 High output CTSUPRRATIO 3 Recommend parameter CTSUPRMODE 10B Base pulse number 62 CTSUSOFF 1 High frequency range noise immunity OFF CTSUSO 00000000B No sensor ICO offset CTSUSNUM 0 Measurement number once The approximate parasitic capacitance connected each TS port is determined using values in Table 4 2 If the parasitic capacitance from the table is under 9pF or over 5OpF there may not be enough sensitivity for a robust system In this case a modification to the layout should be considered or in the case of too little capacitance a small capacitor can be added to the port connection Under 9pF The
23. directions given under Handling of Unused Pins in the manual The input pins of CMOS products are generally in the high impedance state In operation with an unused pin in the open circuit state extra electromagnetic noise is induced in the vicinity of LSI an associated shoot through current flows internally and malfunctions occur due to the false recognition of the pin state as an input signal become possible Unused pins should be handled as described under Handling of Unused Pins in the manual 2 Processing at Power on The state of the product is undefined at the moment when power is supplied The states of internal circuits in the LSI are indeterminate and the states of register settings and pins are undefined at the moment when power is supplied In a finished product where the reset signal is applied to the external reset pin the states of pins are not guaranteed from the moment when power is supplied until the reset process is completed In a similar way the states of pins in a product that is reset by an on chip power on reset function are not guaranteed from the moment when power is supplied until the power reaches the level at which resetting has been specified 3 Prohibition of Access to Reserved Addresses Access to reserved addresses is prohibited The reserved addresses are provided for the possible future expansion of functions Do not access these addresses the correct operation of LSI is not guaranteed if they are acc
24. e is used because it is at the lower end of the linear range of the ICO The second step is to measure Reference ICO count value Finally the value of the CTSUSO register 1s modified until Sensor ICO count and Reference ICO become the same value this means the Sensor ICO is driving 5 uA of the external capacitive load This places it at the lower end of the linear range so there is maximum range for driving additional capacitance It also provides enough margin so the measurement current does not drop down into the lower non linear region It is possible to offset the current about 100uA Since the ICO frequency specification is different with each chip it is recommended that trimming is done on each device This offset process is done automatically by the Renesas driver on initialization and periodically during operation RO1AN2516EU0100 Ver 0 9 Page 27 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution i Approx 20uA CTSURIOA Input value Approx 5uA Approx 25MHz Approx 100MHz 12000 16000 48000 64000 f gt Reference ICO counter output value example Characteristic ICO current frequency Characteristic reference ICO CTSURIOA ICO Counter O Linear area O Non linear area Sensor ICO Sensor ICO Input current Input current Approx 20uA T j S LA OS y A N 12000 16000 48000 64000 Over 20uA current Sensor ico couhterisoverti w
25. e fully responsible for the incorporation of these circuits software and information in the design of your equipment Renesas Electronics assumes no responsibility for any losses incurred by you or third parties arising from the use of these circuits software or information 2 Renesas Electronics has used reasonable care in preparing the information included in this document but Renesas Electronics does not warrant that such information is error free Renesas Electronics assumes no liability whatsoever for any damages incurred by you resulting from errors in or omissions from the information included herein 3 Renesas Electronics does not assume any liability for infringement of patents copyrights or other intellectual property rights of third parties by or arising from the use of Renesas Electronics products or technical information described in this document No license express implied or otherwise is granted hereby under any patents copyrights or other intellectual property rights of Renesas Electronics or others 4 You should not alter modify copy or otherwise misappropriate any Renesas Electronics product whether in whole or in part Renesas Electronics assumes no responsibility for any losses incurred by you or third parties arising from such alteration modification copy or otherwise misappropriation of Renesas Electronics product 5 Renesas Electronics products are classified according to the following two quality grades Standard a
26. ect a touch Electromagnetic field i gt a a mm aa Se A Transmitting electrode Driving pulse Figure 4 6 Basis of Mutual capacitance The basis of Renesas mutual capacitance method is shown in Figure 1 2 The CTSU Capacitive Touch Sensing Unit is constructed using a capacitance current convertor with SCF Switched Capacitor Filter and a current detector The CTSU can represent any parasitic capacitance connected the external port of the MCU as a digital value In addition it includes a pulse generator synchronized with the SCF switching cycle and it is possible to measure the mutual capacitance of electrodes that are placed between SCF port and the pulse output port Driving Voltage Vd 4 Driving pulse Pulse generater TTS af y Parasitic Capacitance Transmitting electrode l Cp E 77 Receiving electrode 1 14 EOS CTS U Mutual Capacitance Vt Cm Current detecter L Capacitance Current TS due Parasitic Capacitance Convertor Cp 47 447 Figure 4 7 Renesas mutual capacitance method In order to measure the capacitance Cm existing on the mutual electrodes the CTSU measures the mutual electrode s capacitance twice The primary measurement measures the capacitance when SCF and the driving pulse are driven to RO1AN2516EU0100 Ver 0 9 Page 20 of
27. encer _ CTSU controller Reference ICO Sensor ICO Figure3 9 Reference counter amp Sensor counter RO1AN2516EU0100 Ver 0 9 Page 14 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 3 3 Firmware 3 3 1 Overview An overview of the software is shown in figure 4 10 The software consists of Physical Driver Middleware API and Application The Physical Driver exchanges data directory with CTSU and exchanges the data with upper layer The Middleware processes the ICO value obtained via Physical Driver and passes it to API It also passes commands specified by the upper layer to Physical Driver The API coordinates the exchange of data between Application layer and Middleware layer The Application processes the data to determine status of touch key slider and wheel It returns ON OFF status of the key and the finger position on the slider and wheel depending on the request of User Application Also it includes the debugger interface to connect with the capacitive touch integrated development environment Workbench6 and USB interface Application Workbench6 Wheel control Key control t User Application WheelDecode Calibration USB MakeCthr CubeSuite e2studio COM Driver Slider control MultiTouchCancel OnOffJudgement SliderDecode DriftCorrection CTSU API CtsuGetDataCheck CtsuGetSensorData Cts
28. erage filters provide Adjusting the number samples averaged can improve rejection of pulses but does increase the response time for a touch Measurement data Figure 5 4 Example of Moving Average Filter b Upper Limit Filter The upper limit filter compares the previous and latest measurement value limits the change in the output to an upper limit Figure 5 8 shows the example of Upper Limit Filter If there is a difference of more than 20 the count value is limited 20 As shown the graph the filter suppress the sudden change of count value and keeps the judgment of touch On or OFF correctly Count value 11500 RAW data 11450 11400 3 Filtered data 11350 11300 11750 JE 11700 3 11150 11100 11050 11000 r 10 10 05 10 1 10 15 10 2 10 25 10 3 10 35 10 4 gt Time Figure 5 5 Example of Upper Limit Filter 5 2 3 Debounce Filter Similar to a mechanical key 1t is desirable to use a debounce filter for cap touch key to reduce the occurrence of false touches due to noise transients It is not actually a debounce filter since touch sensors do not bounce but it performas a similar function Some example shows below a Confirming correspondence with N times This process requires the configured number of same key states On or OFF to occur before the output state changes Basically when a state change is detected subsequent scans are compared if the state is the same a counter 1s incremented I
29. es are TX and which are RX b The measurement period As shown the captor 4 2 2 the measurement period of the mutual capacitance method is twice as long as the measurement period of the self capacitance method because the mutual capacitance method measures the capacitance twice each electrode c Determine of IO driver SCF frequency As same as the self capacitance method it is determined by the measurement of approximately capacitance 4 4 Firmware process 4 4 1 Firmware process of self capacitance method a Measurement process The Cap touch process continuously measures the capacitance continuously and is judges whether the keys are ON or OFF by the change in the capacitance value It is necessary that Cap touch process runs at a periodic rate The CTSU measures the selected TS ports and transfers the result of the measurement from the Registers of Sensor ICO counter and Reference ICO counter to RAM via DTC The firmware process initiates the CTSU scan then once the CTSU measurement end CTSUEN interrupt occurs the firmware reads the results in RAM and processes the data to determine key ON or OFF status The measurement period of the each TS port is approximately 500uSEC For example if 10 TS port are used for key it takes approximately 5mSEC to detect 10 keys A period of Measurement Approx 5mSec TSOTS1 rs TS9 KAprox 500uSec Measurement by CTSU Firmware process gt Trigger to start measurement
30. essed 4 Clock Signals After applying a reset only release the reset line after the operating clock signal has become stable When switching the clock signal during program execution wait until the target clock signal has stabilized When the clock signal is generated with an external resonator or from an external oscillator during a reset ensure that the reset line is only released after full stabilization of the clock signal Moreover when switching to a clock signal produced with an external resonator or by an external oscillator while program execution is in progress wait until the target clock signal is stable 5 Differences between Products Before changing from one product to another e to a product with a different part number confirm that the change will not lead to problems The characteristics of an MPU or MCU in the same group but having a different part number may differ in terms of the internal memory capacity layout pattern and other factors which can affect the ranges of electrical characteristics such as characteristic values operating margins immunity to noise and amount of radiated noise When changing to a product with a different part number implement a system evaluation test for the given product Notice 1 Descriptions of circuits software and other related information in this document are provided only to illustrate the operation of semiconductor products and application examples You ar
31. f the counter reaches the configured value then the output state is changed If the opposite state is RO1AN2516EU0100 Ver 0 9 Page 33 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution encountered once the sequence starts the counter is set to zero Increasing the count value improves rejection but creates delayed response to state changes b Decision by majority This process decides wheher a key is ON or OFF by the taking the majority of the detected states during a fixed period It is faster than the process Confirming correspondence with N times but the canceling of the debounce effect is weaker than above RO1AN2516EU0100 Ver 0 9 Page 34 of 4 Dec 1 2014 RENESAS RX113 Website and Support http www renesas com Inquiries http www renesas com contact All trademarks and registered trademarks are the property of their respective owners RO1AN2516EU0100 Ver 0 9 Dec 1 2014 Design Guide for Renesas Touch Solution RENESAS Page 35 of 4 Revision History Description Rev Date Page Summary General Precautions in the Handling of MPU MCU Products The following usage notes are applicable to all MPU MCU products from Renesas For detailed usage notes on the products covered by this document refer to the relevant sections of the document as well as any technical updates that have been issued for the products 1 Handling of Unused Pins Handle unused pins in accordance with the
32. he measurement is steady when finger is away from electrode as shown by the blue line on the graph The count value increases when finger is approaches and decreases to a steady value when the finger is away again The count value when finger is not close to the electrode is uses as a reference value green dashed line and a threshold value is calculated as a specified difference from that reference value The decision of ON OFF can then be simply determined by checking if the actual count value exceeds the threshold value and switching OFF when the value is under the threshold value Typically the OFF decision also requires that the value goes below the threshold by a specified amount referred to as the hysteresis Sensitivity adjustment of the capacitive touch switch can be done by changing the threshold value Chattering suppression of the switch and the reaction rate can be adjusted by changing the cycle of measurement timing and RO1AN2516EU0100 Ver 0 9 Page 7 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution averaging multiple count values More detail on this is described later Position of finger amp fr iy gt Electrode I Timing of LLELLLELLLELLLLLELLLLLLELLLE I measurement 120 110 me ee ree Measurement Value 100 oun vere Reference value ee e e e m Switch status Figure 2 9 ON OFF switch judgment RO1AN2516EU0100 Ver 0 9 Page 8 of 4 Dec 1 2014 RENESAS RX113 Design
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34. ion or use of controlled substances including without limitation the EU RoHS Directive Renesas Electronics assumes no liability for damages or losses occurring as a result of your noncompliance with applicable laws and regulations 9 Renesas Electronics products and technology may not be used for or incorporated into any products or systems whose manufacture use or sale is prohibited under any applicable domestic or foreign laws or regulations You should not use Renesas Electronics products or technology described in this document for any purpose relating to military applications or use by the military including but not limited to the development of weapons of mass destruction When exporting the Renesas Electronics products or technology described in this document you should comply with the applicable export control laws and regulations and follow the procedures required by such laws and regulations 10 Itis the responsibility of the buyer or distributor of Renesas Electronics products who distributes disposes of or otherwise places the product with a third party to notify such third party in advance of the contents and conditions set forth in this document Renesas Electronics assumes no responsibility for any losses incurred by you or third parties as a result of unauthorized use of Renesas Electronics products 11 This document may not be reproduced or duplicated in any form in whole or in part without prior written consent of Renesas Electron
35. ize the impact on touch detection 5 1 2 Touch Electrode and Wiring Since the touch electrode and wiring act as an antenna the following measures are required to maximize electromagnetic noise immunity and emmissions a Wiring The distance of wiring between touch electrode and touch measurement port should be as short as possible Also capacitive coupling of high speed signal lines can result in noise is superimposed on touch sensing wire if traces run parallel with the high speed signal lines RO1AN2516EU0100 Ver 0 9 Page 31 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution b Position of GND Pattern Improved noise immunity is often achieved by placing a GND pattern in the vicinity of touch electrode and wiring as an electromagnetic shield However when placing GND set the GND pattern as mesh with approximately 3 to 7 copper space ratio this provides improved immunity but minimizes the effect on touch sensitivity due to of parasitic capacitance c ESD Protection The touch overlay panel typically provides ESD protection so it is recommended to ensure adequate breakdown resistant for assumed electrostatic strength Also care should be taken not to generate a gap in the panel joint since there is a possibility that the static electricity can sneak through the gap Figure 5 2 Cases where static electricity sneaks from the gap of the cover panel 5 2 Software Following is the example of s
36. nd High Quality The recommended applications for each Renesas Electronics product depends on the product s quality grade as indicated below Standard Computers office equipment communications equipment test and measurement equipment audio and visual equipment home electronic appliances machine tools personal electronic equipment and industrial robots etc High Quality Transportation equipment automobiles trains ships etc traffic control systems anti disaster systems anti crime systems and safety equipment etc Renesas Electronics products are neither intended nor authorized for use in products or systems that may pose a direct threat to human life or bodily injury artificial life support devices or systems surgical implantations etc or may cause serious property damages nuclear reactor control systems military equipment etc You must check the quality grade of each Renesas Electronics product before using it in a particular application You may not use any Renesas Electronics product for any application for which itis not intended Renesas Electronics shall not be in any way liable for any damages or losses incurred by you or third parties arising from the use of any Renesas Electronics product for which the productis not intended by Renesas Electronics 6 You should use the Renesas Electronics products described in this document within the range specified by Renesas Electronics especially with respect to the maximum rating
37. nsor ICO b Basic current generator Reference ICO amp ICO for spread spectrum The structure of Basic current generator Reference ICO and Spread spectrum ICO is shown in figure 3 6 These two ICO differ in a role The pulse generated in Spread spectrum ICO is eventually sent to I O Driver and used for frequency diffusion of drive pulse of SCF The other Reference ICO is used for comparison of Sensor CO which is mentioned above Detail of how to use is described later respectively Current modulation V 3 From Power unit Basic current generator Voltage Current Current Spread spectrum ICO mirror Modulator To digital control Regulator Current offset Current mirror To digital control Figure3 6 Basic current generator Reference ICO amp for spread spectrum Basic current generator is structured by Voltage Regulator to supply electric current with a constant voltage and Current Modulator and Current Offset that supply controlled electric current to ICO through Current mirror Voltage Regulator is the same as the structure of Voltage Regulator in Touch VDD Regulator above and supplies a constant voltage to subsequent current through Current mirror Current modulator modulates electric current outputting from RO1AN2516EU0100 Ver 0 9 Page 12 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution Voltage Regulator in order to diffuse frequency of subsequent ICO for spread spectr
38. oftware filters 5 2 1 Drift Correction Process The capacitive touch measurement is influenced by environmental changes such as temperature humidity and aging of member These gradual changes are compensated for using the drift compensation process shown in Figure 5 6 As mentioned above threshold value above which a touch is determined to occur is calculated from the reference value This reference value is periodically updated to compensate for environmental changes the compensation is held off when a touch has been determined The update rate of the reference value is configurable If it is too fast the reference may react as a finger is approaching and start to compensate which may result in loss of touch sensitivity If itis very slow false touches may occur due to changes in environmental conditions Measurement value Count Value Threshold value Reference value Touch OFF Touch ON Touch OFF Time gt Figure 5 3 Drift Correction Processing 5 2 2 Countermeasure of Random Noise Software filters are also used to compensate for random or electromagnetic noise The following is the example of software filter RO1AN2516EU0100 Ver 0 9 Page 32 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution a Moving Average Filter The Renesas solution utilizes a moving average filter as described in figure 5 7 In the example the measurement averages the last 4 values Moving av
39. ormula 1 5 Notice another benefit 1s the parasitic capacitance is cancelled in the result RO1AN2516EU0100 Ver 0 9 Page 21 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution b Button design of the mutual capacitance method Figure 2 1 shows the recommended pattern for a mutual button The outside pattern is the transmitting electrode Tx and inside is the receiving electrode Rx Transmitting Receiving electrode electrode Rs Figure 4 8 the sample of the button pattern by the mutual capacitance method In order to increase the capacitance the opposing areas of the transmit and receive surface should be kept large The opposing surfaces form the plates of the coupling capacitance The recommended area of the button is from 10x10 to 16x16 mm It is possible to construct a button larger than 16 x16mm button but there will be little increase in the sensitivity of the mutual field influence and you have to consider the effect of the parasitic capacitance 1 0xPanel Thickness 0 6xPanel Thickness Up to 0 5mm Figure 4 9 the electrode pattern width Figure 2 2 shows the electrode pattern width To reduce the parasitic capacitance the width of Rx pattern is recommended less than 0 5mm The actual width used depends on the resistance of the pattern material When the material resistance is large ex Carbon film the width will have to be increased to keep the resistance small It is recommended to keep
40. ost at over 1 OOMHz and at very low frequencies Shown the upper left of Figure 4 9 The characteristic of frequency and current also varied among individual chips In order to compensate for variation in each by each chip a Reference CO is used The characteristics of Sensor ICO and Reference ICO are well matched since they have same basic construction and are on the same die The Sensor ICO is driven by the current that is generated by the IO driver and TSCAP voltage the Reference ICO is driven by the current that 1s generated and controlled by a register setting 0 19 5uA The linear range of the Reference ICO is shown the upper right of Figure 4 9 this region corresponds to register value between OxO3FF and OxOFFF It shown blue line circled area in Figure 4 9 Since the Sensor ICO frequency is determined the current supplied by IO driver to the external capacitance will often exceed the linear range of the ICO Refer the lower left of Figure 4 9 To prevent the ICO current going outside the linear range of ICO a current offset function is used This offset current supplies a portion of the current required to drive the external capacitance to reduce the CO measured current back into the linear range Refer the lower right of Figure 4 9 The CTSUSO amp CTSURIOA registers are used for trimming the current The process is to first write Ox3FF to CTSURIOA which will set the current supplied to the Reference ICO to approximately 5uA The 5 uA valu
41. pacitance Current Conversion A Switched capacitor filter SCF is used to convert the capacitance described in the chapter 2 1 to a current that is proportional to that capacitance The SCF is created using a capacitor power two switches and the control signal to toggle two switches ON OFF alternatively Swi Control pulsa KZ Control pulse Figure 2 4 SCF configuration and Charge and discharge operation of capacitor SW 1 and SW2 are controlled by the pulse so when one turns ON and the other turns OFF When SW1 turns ON and SW2 turns OFF the capacitor is charged as described in Figure 2 4 left After switching SW1 to OFF SW2 to ON the capacitor is discharged as describe in Figure 2 4 right RO1AN2516EU0100 Ver 0 9 Page 5 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution e gt gt Figure 2 5 the status of SW1 and SW2 and the relationship of electric current i Figure 2 5 shows he status of SW as they are repeatedly turning ON and OFF and the relationship of current 1 in the circuit The electric charge of the capacitor is O at the moment SW1 turns ON and the current flows into capacitor rapidly As the charge of the capacitor progresses the current decreases and the current stops at full of charge After that the electric charge of capacitor flows into the ground when SW2 turns ON This current Figure 2 5 dashed line does not appear on the power supply side because SW1 turns
42. rge it is difficult to detect the small change in the overall value A second method of sensing capacitance is the mutual capacitance method With this method a pair of electrodes are used in contrast with the self capacity method with a single electrode An example of mutual capacity method is shown in Figure 2 3 The mutual capacity method is configured using a receiving electrode transmitting electrode and pulse generators When pulses are sent to the transmitting electrode energy is transferred by field coupling to the receiving electrodes If a human body approaches part of the electric field moves to the human body and the electric field between electrodes decrease It is possible to detect the approach of a human body by measured the decrease in energy couple to the receiving electrode The circuit of the mutual capacity method is more complicated than self capacity method However it is possible to decrease the influence of parasitic capacity which is a problem in a self capacity method and also possible to increase the strength of electric filed generated which provides highly sensitive detection A key application is for touch screens RO1AN2516EU0100 Ver 0 9 Page 4 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution Field coupling To detector To detector Transmitter JUL A a a maaan A Reciever Transmitter Reciever TUL Figure 2 3 Mutual capacity method 2 2 Ca
43. rges and discharges continually This alternating current is smoothed by the power supply circuit connected SCF The current is sent to the current oscillator that varies oscillation frequency in proportion to current The output of the oscillator is sent to the counter The counter counts the number of pulses during a specified time The graph in the figure shows an example when the frequency of SCF is fixed and the capacitance value is doubled the current and the frequency of current oscillator double The resulting count value measured by counter also doubles from 6 to 12 in this example Power supply circuit Current Oscillator Counter From SCF Counter value gt Ix In t i t Current wave form of SCF Current wave form after Wave form of Current Oscillator Wave form of Count passing Smoothing circuit Figure 2 8 Flow of current digitization 2 4 ON OFF switch judgment As explained in chapter 2 1 for self capacitance method it is possible to judge the increase of capacitance when human body has touched or is close to the electrode This is done by regularly performing the capacitance measurement process described above and measuring the changes of the counter value The process flow of deciding whether a switch is ON OFF when finger approaches the electrode and then moves away again is shown in Figure 2 9 Measurement of the capacitance is carried out at a regular interval as shown in the figure The count value obtained by t
44. rom data that was collected by API Calibration processing Follow up correction processing of measurement data to environmental changes ON OFF processing of the key Detection processing of slider and wheel position User s applications such as system control of the product and display of LED and LCD 4 Designing a Touch Board and System 4 1 Overview This chapter shows how to construct Cap touch key with CTSU Overall order is as follows Design of Cap touch key board Preparing the firmware for Cap touch Tuning the sensitivity of Cap touch key Evaluation including the noise immunity test 4 2 Design of Cap touch board 4 2 1 Design of the self capacitance method Cap touch key board a Basis of the capacitance Figure 4 1 shows the capacitance model The capacitance defined by the following formula e tis proportional to electrode surface area A e tis proportional to the relative permittivity of the inter electrode material e tis in inversely proportion to the distance of inter electrode O C KE p A d C Capacitance Panel A Electrode area d Interelectrode distance Electrode 9 Electric constant K Relative permittivity To Touch Sensor device O Figure 4 1 Capacitance model Capacitive touch detects the touch of the human body using these characteristics A capacitive touch detector measures the capacitance between the human body and the electrode as shown Fig
45. structure of AFE is shown in figure 3 4 AFE primarily consists of a power generation part and ICO part The capacitance that is converted to current in I O Driver part is converted to frequency in AFE part and sent to Digital control part uy MCU basic voltage Regulator Spread spectrum ICO Basic current Generator _ To digital control Regulator LPF From O Driver Figure 3 4 Analog Front End RO1AN2516EU0100 Ver 0 9 Page 11 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution a Touch VDD regulator amp Sensor ICO The structure of Touch VDD Regulator is shown in figure 3 5 Touch VDD Regulator is structured by Voltage Regulator that supplies voltage to I O Driver Current offset to offset the detected electric current and current mirror that passes electric current to ICO part ICO is an oscillator that changes oscillating frequency depending on the input electric current and increases the number of frequency in proportion to the increase of the current Current offset is a mechanism to offset the amount of electric current in order to reduce the influence of the parasitic capacitance included in the current that is measured as an electrostatic capacitance Detail is described later From Power unit Current oltset Touch VDD Regulator Voltage Regulator Current amp offset Current mirror To digital control From I O Driver Figure3 5 Touch VDD Regulator amp Se
46. t performs touch detection and determination of finger position on a slider or wheel Middleware API provides interface to User application User Application API Middleware Software Layer Physical Driver Digital Control Analog Front End Hardware I O Driver R01AN2516EU0100 Ver 0 9 Page 9 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 3 2 Hardware 3 2 1 Overview An overall view of hardware is shown in figure 3 2 The hardware is divided into I O Driver Analog Front End Digital Control and CPU Basic operation is as follows 1 The current output from the I O Driver changes when a finger approaches an electrode which is connected to I O Driver Only one I O Drivers is active at a time and the drive pulse signals are switched sequentially There is a single Pulse Generator but multiple I O drivers are used to measure multiple electrodes 2 lO Driver current is smoothed by an external low pass filter LPF and sent to the current controlled oscillation circuit ICO which converts changes in current to changes in frequency 3 The Digital Control circuit counts the pulses from the ICO for a specified period of time This count value which is proportional to the capacitance is then stored in a register 4 The count value is automatically transferred to RAM through data transfer circuit DTC A measurement completion interrupt is sent to CPU at the same time as the data transfer
47. the Tx pattern the same thickness as the cover panel The distance of Rx and Tx should be 0 6 x thickness of cover panel If there is a conflict between these trace thicknesses and the parallel areas of the Rx and Tx surface the opposing area is a higher priority c Wiring When sensing using the mutual method the Rx trace layout is the most critical Noise injection from other wirings and the parasitic capacitance with GND pattern can become problems This section details examples of routing In order to prevent unanticipated capacitive coupling between Tx and Rx wiring Tx and Rx wiring should be separated as far as they practical At a minimum the distance should be more than a finger touch distance as shown Figure 3 1 In addition if Tx and Rx must cross it 1s recommended to wire orthogonal and to minimize any parallel traces as shown Figure 3 2 RO1AN2516EU0100 Ver 0 9 Page 22 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution TX Rx Figure 4 10 Tx and Rx wirings distance Rx Figure 4 11 In case of crossing Tx and Rx wirings The trace length from the Rx MCU port pin should be kept as short as possible to minimize the parasitic capacitance and series resistance We recommend keeping the parasitic capacitance under 20pF and the resistance under 2Kohm as shown Figure 3 3 Rx wiring Parasitic capacitance under Total resistance under Damping resisters Figure 4 12 Parasitic capacitance and
48. uGetReferenceData etc a E1 Debugger E1 Debugger Workbench VF Touch common control CTSUMainProc MovingAverage CTSUSetCtsuStart USB driver CTSUSetWriteBuffer CTSUSetInitial CTSUFunctionPinControl E CTSUStartSetup CTSUParameterBufinit D p m g a i 4 nysical Driver physical_driver El VF H W RX113 prm PA VE 4 Workbench module Figure 3 1 Overview of the firmware structure 3 3 2 Physical Driver The Physical Driver provides the functions to access all the registers of the CTSU It reads out and returns the data from the registers in order to respond to the request from upper layer Also it receives the write requests from upper layer and writes the value to the resister 3 3 3 Middleware Middleware provides initialization of CTSU including the DTC initialization for transferring the CTSU resister value averaging of ICO value and register setting 3 3 4 API API provides functions to exchange the data between Application and Middleware CTSU measurement mode setting API CTSU measurement data acquisition confirmation API CTSU sensor ICO measurement data acquisition API For the detail of the see the application note RO1AN2516EU0100 Ver 0 9 Page 15 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution 3 3 5 Application The Application provides touch key slider and wheel processing It performs the following processing f
49. um As shown in the graph of figure 3 6 as a result waveform that ICO for spread spectrum output is modulated to FM and sent to Drive pulse generator of Digital control part Current Offset controls the output frequency of subsequent Reference ICO by restricting the current output from Voltage Regulator 3 2 4 Digital Control amp CPU unit Digital control and CPU unit is shown in figure 3 7 Digital control is structured by counter to count output pulse of ICO Drive pulse generator to generate drive pulse of I O Driver based on FM modulation pulse of ICO and Sequencer to control sequence operation for whole CTSU and Register group to exchange the data with CPU CPU unit exchanges the data with CTSU through DTC Data Transfer Controller or Register and execute a process involved in the touch switch in accordance with algorism of software Digital control Sequencer CTSU controller Drive pulse Generator From AFE CTSU Control register as i ce CPU core Timer serial To Drive pulse switch matrix Flash I O Figure3 7 Digital control amp CPU unit a Drive pulse generator The structure of Drive pulse generator is shown in figure 3 8 Drive pulse generator is structured by Clock pulse generator Phase shifter Polynomial counter and Mixer Input from CPU oscillator is divided to an appropriate frequency in Clock pulse generator and sent to Phase shifter Phase shifter follows the instruction from Polynomial counter
50. ure 4 1 Higher sensitivity and noise immunity is provided by a bigger capacitance difference between non touch and touch A large sensor area will provide improved accuracy of the touch detection and high noise immunity However the increased sensitivity is also related to the touch area of the finger and it is not effective to increase surface area of the electrode past some value The inter electrode distance depends on thickness of the material with which the surface of the touch key is covered Table 4 1 shows the relative permittivity of some common materials It is different according to each material Glass has the best relative permittivity excluding water Acrylic and plastic are also often used R01AN2516EU0100 Ver 0 9 Page 16 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution Table 4 1 the relative permittivity of some common materials Dielectric Material ik Flexible Vinyl Film Water so b Electrode shape The recommended size of the electrode is in forms of e or E with an area of 10mmx10mm to 15mmx15mm A triangular A or E shape pattern is not recommended since the electrode acts as antenna and can be easily affected by noises Lighting with LED lights from the back of the electrode is also effective when it is formed is in a donut shape or mesh configuration However in those forms the sensitivity of the electrode can be weakened due to decreased area or noise can be created by the PW
51. y design consideration for the user board These noise immunities are explained in this chapter RO1AN2516EU0100 Ver 0 9 Page 30 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution Figure 5 1 Disturbance factors to affect the touch measurement 5 2 Noise Immunity on the Board 5 2 1 Power Supply Circuit The stability of the power supply to the MCU is a key component in noise rejection Following 1s the precautions and measures a Using 3 terminal regulator We recommend using 3 terminal regulator in order to remove ripple component of power supply b Peripheral ports of the port used for the touch measurement Port pins that are part of a port output group that has touch capability but are being used for other functions should not be utilized for high speed high current operations such as PWM drive of LED sound output and serial communication High current switching on ports where a TX port of a mutual configuration are sensitive to internal Vcc variations due to high current demands which drop the drive Vcc and result in a touch measurement that is unstable c Inserting the Ferrite Core If the conducted noise from the power supply line or human body is assumed it is recommended to insert a ferrite core to the power supply line d Separation of Power When sharing the power with other devices it is recommended to isolate the touch MCU power from other switching loads on the same source to minim
52. y signal lines such as PWM output and serial communications If the sensor line must cross noisy signals it is recommended to cross them on opposite sides of the board and at a right angle as shown Figure 4 5 Figure 4 5 shows the parasitic capacitance and the resistance on the cap touch key board The parasitic capacitance exists between the electrode the electrode wiring the connecter and the GND pattern the metal frame and the signal line The maximum capacitance that CTSU can support is 5OpF so the board and system design should control the parasitic capacitance so the total of the parasitic is SOpF or less It is also recommended to design the board so the parasitic capacitance is at least 10 pF because small capacitances result in worse noise immunity In addition it is recommended to insert a damping resistance between the electrode and TS port to protect from surge breakdown and to improve the noise immunity The impedance between the electrode and TS port effects the frequency of SCF and the sensitivity therefore the recommend the total resistance including the damping resistance is under 2Kohm RO1AN2516EU0100 Ver 0 9 Page 18 of 4 Dec 1 2014 RENESAS RX113 Design Guide for Renesas Touch Solution Total Resistance 2K or less gt Parasitic Capacitance Resistor contact point material inherent Metal chassis Figure 4 4 the parasitic capacitance and the resistance on the board
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