SL871 Hardware User Guide
Contents
1. 7 S AA a A a PP gt e L 1 2 p 54 d ri b TU L4 P Pm KIN i 5 4 SY i S LEAN sia NG ihi 8 Led STE A fa e MIX b s g 8 x LAME DN ZC lt s 1 i e i Jh i ps mm TE LAE 4 ta ke F Inm wu Hi e bh az e A 7 p i EJ e d wa MM ma 2 p Uis i nt M a T E Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 27 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 6 Reference Design The SL871 Reference Design is presented in the figure below V ANT Top View L1 35 5nH GND vc MEME HEIN VCC C5 100pf GND Reserved Reserved VCCBK VCCRF Reserved Reserved Timepulse Reserved RxD EMEEL Reserved no MEME gt x Reserved GND e ew pe Gul NG E DD WT um ecd ims Figure 4 SL871 Reference Design Active Antenna Along with power and ground the minimum number of signals required to operate the SL871 properly are four digital signals and one RF signal The RF input can be connected directly to a GNSS antenna The reference design however shows a DC power feed for an active antenna C5 is used to block the DC voltage from entering the SL871 The inductor L1 is chosen to be self resonant at the GNSS frequency approximately 1 57542 GHz to minimize loading on the RF trace Capacitor C62. E s ge L KK 7 PAGAN gt Ae D t E y p en ke Dm a IY a P di O D E b M Gd g R li K e a D Ki nd Ki TET d al M TITE Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 30 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 6 2 Advanced Features 6 2 1 CW Jamming Detection The SL871 module detects tracks and removes narrow band interfering signals jammers without the need for external components or tuning The Jamming Remover is an embedded interference suppression that tracks and removes up to 12 CW Carrier Wave type signals up to 80 dBm total power signal levels By default the interference suppression is disabled and usage requires a PMTK command to enable it This is over and above the excellent SAW filter response that exists before the GPS LNA input This feature is useful both in the design stage and during the production stage for uncovering issues related to unexpected jamming 6 2 2 SBAS The SL871 receiver is capable of using Satellite Based Augmentation System SBAS satellites as a source of both differential corrections and satellite range measurements These systems WAAS EGNOS MSAS use geostationary satellites to transmit regional differential corrections via a GNSS compatible signal The use of SBAS corrections can improve typical position accuracy to 3
3. lelit 51871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 4 l OPins 4 1 4 2 4 3 UARI The SL871 module includes a Universal Asynchronous Receiver Transmitter UART serial interface RxD TxD that supports configurable baud rates The signal output and input levels are 0 V to VCC An interface based on RS232 standard levels 12 V can be implemented using level shifters such as Maxim MAX3232 Hardware handshake signals and synchronous operation are not supported Reset Driving RESET N low activates a hardware reset of the system Use this pin only to reset the module Do not use RESET NN to turn the module on and off since the reset state increases power consumption Time Pulse The TIMEPULSE PPS output signal provides a pulse per second output signal for timing purposes The SL871 time pulse signal is one pulse per second The PPS output is valid when navigation is valid and will also continue to freewheel after a valid fix 1s lost by a certain navigation DR timeout of typically 10 seconds Pulse length high is 100ms and UTC sync is at rising edge an forbidden without written authorization from Telit Communications S p LA All Rights Reserved Page 15 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 a RF Front End Design The SL871 contains a pre select SAW filter This allows the SL871 to work well with a passive GNSS antenna For improved performance or
4. ba 34 Ji e o A vi E p q D A PIN H d UN N K i d gt e E D 7 pa AP bi L3 Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 31 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 7 Handling and soldering 7 1 Moisture Sensitivity The SL871 module has a moisture sensitivity level rating of 3 as defined by IPC JEDEC J STD 020 This rating is assigned due to some of the components used within the SL871 The SL871 is supplied in trays or tape and reel and is hermetically sealed with desiccant and humidity indicator card The SL871 parts must be placed and reflowed within 168 hours of first opening the hermetic seal provided the factory conditions are less than 30 C and less than 60 and the humidity indicator card indicates less than 10 relative humidity If the package has been opened or the humidity indicator card indicates above 10 then the parts will need to be baked prior to reflow The parts may be baked at 125 C 5 C for 48 hours However the trays nor the tape and reel can withstand that temperature Lower temperature baking is feasible if the humidity level is low and time is available Please see IPC JEDEC J STD 033 for additional information Additional information can be found on the MSL tag affixed to the outside of the hermetical seal bag NOTE JEDEC standards are available for free f
5. wireless solutions Teli SL871 Hardware User Guide 1VV0301147 Preliminar r0 2014 04 11 18 b iat DO gt A E f P E PURA AT i A DAD s m ct m A oss ree a v s AA Ee a Making machines talk i elit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 APPLICABILITY TABLE PRODUCT 3 e SE e i gt a CT x i E G 38 i e po e DP ef o T VA A a b LAM m M 1 4 e BN ger Si dn d 3 i SOT s s T zl t AN the EN r E Bech 7 NB EO E e O per Ze ke F Y Zi gt lt s i it NI a SA ut v e Segel A p jp 7 e B a 4 x E 5 d pr bk e 7 3 DECKEN z yc n Pa a DG j Ee Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 2 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE Notice While reasonable efforts have been made to assure the accuracy of this document Telit assumes no liability resulting from any inaccuracies or omissions in this document or from use of the information obtained herein The information in this document has been carefully checked and is believed to be entirely reliable However no responsibility is assumed for inaccuracies or omissions Telit reserves the right to make changes to any products describ
6. an urban canyon environment then the number of satellites in view could drop below that needed to determine a 3D solution This is a case where a bad signal may be better than no signal The system designer needs to make tradeoffs in their application to determine the better choice 5 3 GNSS Antenna Gain Antenna gain is defined as the extra signal power from the antenna as compared to a theoretical isotropic antenna equally sensitive in all directions For example a 25mm by 25m square patch antenna on a reference ground plane usually 70mm by 70mm will give an antenna gain at zenith of 5 dBic A smaller 18mm by 18mm square patch on a reference ground plane usually 50mm by 50mm will give an antenna gain at zenith of 2 dBic While an antenna vendor will specify a nominal antenna gain usually at zenith or directly overhead they should supply antenna pattern curves specifying gain as a function of elevation and gain at a fixed elevation as a function of azimuth Pay careful attention to the requirement to meet these specifications such as ground plane required and any external matching components Failure to follow these requirements could result in very poor antenna performance It is important to note that GNSS antenna gain is not the same thing as external LNA gain Most antenna vendors will specify these numbers separately but some combine them into a single number It is important to know both numbers when designing and evaluating the
7. canyons narrow roads surround by high rise buildings so challenging In general the reflecting of the GNSS signal causes the polarization to reverse The implications of this are covered in the next section d S P 3 d ei kd Xi k Di d e KA E A S f d ta h 7 s La 4 m Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 17 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 5 2 GNSS Antenna Polarization The GNSS signal as broadcast is a right hand circularly polarized signal The best antenna to receive the GNSS signal is a right hand circularly RHCP polarized antenna Remember that IS GNSS 200E specifies the receive power level with a linearly polarized antenna A linearly polarized antenna will have 3 dB loss as compared to an RHCP antenna assuming the same antenna gain specified in dBi and dBic respectively An RHCP antenna is better at rejecting multipath than a linearly polarized antenna This is because the reflected signal changes polarization to LHCP which would be rejected by the RHCP antenna by typically 20 dB or so If the multipath signal is attenuating the line of sight signal then the RHCP antenna would show a higher signal level than a linearly polarized antenna because the interfering signal is rejected However in the case where the multipath signal is replacing the line of sight signal such as in
8. gt lt H d p be F A s A 1 M HE ke NE C a e E H BL E SS ae madiih AI n forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 35 of 35
9. if the antenna cannot be located near the SL871 an active antenna that 1s an antenna with a low noise amplifier built in can be used The following items will be discussed in turn to assist in designing the RF front end RF signal requirements GNSS antenna polarization GNSS antenna gain System noise floor Active versus passive antenna RF trace losses Implications of the pre select SAW filter External LNA gain and Noise Figure Powering the external LNA active antenna 10 RF interference 11 Shielding ORIAURONP 5 1 RF Signal Requirements The SL871 can achieve Cold Start acquisition with a signal level of 148 dBm at its input This means the SL871 can find the necessary satellites download the necessary ephemeris data and compute the location within a 5 minute period In the GNSS signal acquisition process downloading and decoding the data is the most difficult task which is why Cold Start acquisition requires a higher signal level than navigation or tracking signal levels For the purposes of this discussion autonomous operation is assumed which makes the Cold Start acquisition level the important design constraint If assistance data in the form of time or ephemeris aiding is available then even lower signal levels can be used to compute a navigation solution The GNSS signal is defined by IS GNSS 200E This document states that the signal level received by a linearly polarized antenna having 3 dBi gain will be a mi
10. one Hz bandwidth This is a standard method of measuring GNSS receiver performance The simplified formula is 174dbm SNF GNSS Signal level C No Thermal noise is 174 dBm Hz at 290K From this we can compute a system noise figure of 4 dB for the SL871 This noise figure consists of the loss of the pre select SAW filter the noise figure of the LNA as well as implementation losses within the digital signal processing unit If a good quality external LNA is used with the SL871 then the noise figure of that LNA typically better than 1dB could reduce the overall system noise figure of the SL871 from 4 dB to around 2 dB Some of the factors in the system noise figure are implementation losses due to quantization and other factors often referred to a digital noise or DSP noise and don t scale with improved front end noise figure but are additive The digital noise is typically around 1 0 1 5dB See Section 5 9 for more information about reducing system noise by adding an external LNA 5 5 Active versus Passive Antenna If the GNSS antenna is placed near the SL871 and the RF trace losses are not excessive nominally 1 dB then a passive antenna can be used This would normally be the lowest cost option and most of the time the simplest to use However if the antenna needs to be located away from the SL871 then an active antenna may be required to obtain the best system performance The active antenna has its own built in low noise amplifier to
11. overcome RF trace or cable losses after the active antenna However an active antenna has a low noise amplifier LNA with associated gain and noise figure In addition many active antennas have a pre select filter a post select filter or both 5 6 RF Trace Losses RF Trace losses are difficult to estimate on a PCB without having the appropriate tables or RF simulation software to estimate what the losses would be A good rule of thumb would be to keep the RF traces as short as possible make sure they are 50 ohms impedance and don t contain any sharp bends d S P 3 d ei kd Xi k Di d e KA E A S f d ta h 7 s La 4 m pa ERD Bruine g Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 19 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Incorrect avoid right angle Correct keep RF trace short and direct ek e m CERO GEHE ua pa E Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 20 of 35 9 7 lelit 51871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 PCB stack and Trace Impedance It s important to maintain a 500hm trace impedance on the RF path on the host board where the module is mounted to Design software for calculating trace impedance can be found from multiple sources on the internet Below
12. the position when the velocity falls below a threshold indicating that the receiver is stationary The heading is also frozen and the velocity is reported as 0 The solution is then unpinned when the velocity increases above a threshold or when the computed position is a set distance from the pinned position indicating that the receiver is in motion again Note that these velocity and distance thresholds cannot be changed By default static navigation is disabled It can be enabled by sending a Static Navigation message command 1 This feature is useful for applications in which very low dynamics are not expected the classic example being an automotive application 6 1 3 Velocity Dead Reckoning Velocity dead reckoning refers to the use of the last known velocity to propagate the navigation solution when there are insufficient measurements to calculate an updated solution It serves to mitigate the effects of blocked satellite signals by continuing to provide a position output Note that the receiver outputs status information which indicates whether a solution is being maintained using dead reckoning By default the receiver operates in dead reckoning mode for up to 10 seconds before invalidating the position This timeout value is considered to be appropriate for most applications It can be changed using the Mode Control message Message ID 136 Valid timeout values are in a range from zero which disables dead reckoning to two minutes
13. A Be RK kat P P j Se PS eg f 5 ch D SZ ZC gt a j 3 ae E Jh i ps wey Ji i 2 d f DUN r pe F Inm wu Hi e bh az e p NG Ba R H ng B i i E d ma i ac GER E nt M a L E Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 33 of 35 i elit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 8 PCB Layout Details The PCB footprint on the receiving board should match the SL871 pad design shown below The solder mask opening is generally determined by the component geometry of other parts on the board and can be followed here Standard industry practice is to use a paste mask stencil opening the same dimensions as the pad design DATUM A A 9 7040 10 DATUM B m 10 1020 10 DP ee 2 45x0 15 Figure 6 SL871 Mechanical Dimensions i lt KE Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 34 of 35 A 4 e e x ro ai Oe Md IG elit 51871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 9 Document History keck Reproductio Revision Date Changes 0 2014 0411 First Preliminary issue E e ES EEE NM i rr eee e r 1 mp L4 5 mg P ek 4 3 j e i NA sar ANG 1 OO x lt L
14. NA should have a noise figure better than 1 dB This will give an overall system noise figure of around 2 dB assuming the LNA gain is 14 dB or if higher the low gain mode is selected within the SL871 The overall system noise figure can be calculated using the Friss formula for cascaded noise figure The simplified formula 1s shown below F5 1 Fa 1 F 1 F 1 1 Gy H G1G5 G1GoG3 bi aa Gi1G3Ga G4 4 F is the total system noise F1 is the noise figure of the external LNA F2 is the noise figure of the internal LNA and G1 is the gain of the external LNA In the GPS receiver the Digital noise is an additive number and cannot be reduced by reducing the System Nosie figure d S P 3 d ei kd Xi k Di d e KA E A S f d ta h 7 s La 4 m Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 24 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 F 1dB 3 1 15 1 1 dB approx System Nosie 1 1 1 0 1 5 dB Digital Noise System Nosie 2 1 2 6 dB External LNA G 14 dB 1dB NF GPS LNA G 15 dB 2 5 3 0 dB 1 5 DSP noise Approximately 4 0 4 5dB System Equivalent Noise Figure 4 Cascade Nosie Figure calculations with external LNA The external LNA if having no pre select filter needs to be able to handle signals other than the GNSS signal These signals are typically at much h
15. SS signal is heavily influence by attenuation due to foliage such as tree canopies etc as well as outright blockage caused by building terrain or other items in the line of sight to the specific GNSS satellite This variable attenuation 1s highly dependent upon GNSS satellite location If enough satellites are blocked say at a lower elevation or all in a general direction the geometry of the remaining satellites will result is a lower accuracy of position The SL871 reports this geometry in the form of PDOP HDOP and VDOP For example in a vehicular application the GNSS antenna may be placed embedded into the dashboard or rear package tray of an automobile The metal roof of the vehicle will cause significant blockage plus any thermal coating applied to the vehicle glass can attenuate the GNSS signal by as much as 15 dB Again both of these factors will affect the performance of the receiver Multipath is a phenomena where the signal from a particular satellite 1s reflected and is received by the GNSS antenna in addition to or in place of the original line of sight signal The multipath signal has a path length that is longer than the original line of sight path and can either attenuate the original signal or if received in place of the original signal can add additional error in determining a solution because the distance to the particular GNSS satellite is actually longer than expected It is this phenomena that makes GNSS navigation in urban
16. by moving ground plane avoids mismatches Figure 2 Avoid Narrow RF trace ra 3 R Aue 4 fi 5 si p3 LL ee l i A BN gg EOE Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 22 of 35 Calculate Esseg Calculate 20 F4 new board thickness el 566 0 80 10 i elit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Solder Resist 25u Cu 36 PRERE 7 Remove ground PS plane CORE 457 24 Wa Minis ew Ground EN Plane Solder Resist 25g Will provide 50 ohm impedance a 80 Elect Lengh 0251 Ja pes cet Lengh 302 re ry degrees Taas LOWaveenghs 3983356 m ba H Vp fraction of c Frequency 15 ec v este eenig be v o Em Figure 3 Wider Trace width achieved by moving ground plane Ha forbidden without written cm from Telit Communications s p A All Rights Reserved Page 23 of 35 lelit 51871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 5 8 Implications of the Pre select SAW Filter The SL871 module contains a SAW filter used in a pre select configuration with the built in LNA meaning the RF input of the SL871 ties directly into the SAW filter Any circuit connected to the input of the SL871 would see a complex impedance presented by the SAW filter particularly out of band rather than the relatively broad and flat return loss pres
17. e User Guide 1VV0301147 Preliminary r0 2014 04 11 Document Organization This document contains the following chapters sample Chapter 1 Introduction provides a scope for this document target audience contact and support information and text conventions Chapter 2 Powering the SE868 gives an overview about power supply Chapter 3 Updating Firmware describes the SW updating procedure for Flash version Chapter 4 Updating Patch code describes how to apply patch code to ROM version Chapter 5 Main serial interface describes the serial interface Chapter 6 MEMS sensor and EEPROM Interface describes the DR I2C interface Chapter 7 RF Front End Design describes in details the characteristics of the Front end D Chapter 8 Reference Design gives an overview about the reference design Chapter 9 Firmware configuration describes the configuration settings Chapter 10 Handling and soldering describes packaging and soldering of the module Chapter 11 PCB layout details describes the mechanical design of the module Chapter 12 Document History describes the history of the present product Text Conventions Danger This information MUST be followed or catastrophic equipment failure or bodily injury may occur Caution or Warning Alerts the user to important points about integrating the module if these points are not followed the module and end user equipment may
18. ed herein and reserves the right to revise this document and to make changes from time to time in content hereof with no obligation to notify any person of revisions or changes Telit does not assume any liability arising out of the application or use of any product software or circuit described herein neither does it convey license under its patent rights or the rights of others It is possible that this publication may contain references to or information about Telit products machines and programs programming or services that are not announced in your country Such references or information must not be construed to mean that Telit intends to announce such Telit products programming or services in your country Copyrights This instruction manual and the Telit products described in this instruction manual may be include or describe copyrighted Telit material such as computer programs stored in semiconductor memories or other media Laws in the Italy and other countries preserve for Telit and its licensors certain exclusive rights for copyrighted material including the exclusive right to copy reproduce in any form distribute and make derivative works of the copyrighted material Accordingly any copyrighted material of Telit and its licensors contained herein or in the Telit products described in this instruction manual may not be copied reproduced distributed merged or modified in any manner without the express written permission of T
19. elit Furthermore the purchase of Telit products shall not be deemed to grant either directly or by implication estoppel or otherwise any license under the copyrights patents or patent applications of Telit as arises by operation of law in the sale of a product Computer Software Copyrights The Telit and 3rd Party supplied Software SW products described in this instruction manual may include copyrighted Telit and other 3rd Party supplied computer programs stored in semiconductor memories or other media Laws in the Italy and other countries preserve for Telit and other 3rd Party supplied SW certain exclusive rights for copyrighted computer programs including the exclusive right to copy or reproduce in any form the copyrighted computer program Accordingly any copyrighted Telit or other 3rd Party supplied SW computer programs contained in the Telit products described in this instruction manual may not be copied reverse engineered or reproduced in any manner without the express written permission of Telit or the 3rd Party SW supplier Furthermore the purchase of Telit products shall not be deemed to grant either directly or by implication estoppel or otherwise any license under the copyrights patents or patent applications of Telit or other 3rd Party supplied SW except for the normal non exclusive royalty free license to use that arises by operation of law in the sale of a product 4 TITE NE mee Reproduction forbidden w
20. ented by the LNA Filter devices pass the desired in band signal resulting in low reflected energy good return loss and reject the out of band signal by reflecting it back to the input resulting in high reflected energy bad return loss If an external amplifier is to be used with the SL871 the overall design should be checked for RF stability to prevent the external amplifier from oscillating Amplifiers that are unconditionally stable at the output will be fine to use with the SL871 If an external filter is to be connected directly to the SL871 care needs to be used in making sure the external filter or the internal SAW filter performance is not compromised These components are typically specified to operate into 50 ohms impedance which is generally true in band but would not be true out of band If there is extra gain associated with the external filter then a 6 dB Pi or T resistive attenuator is suggested to improve the impedance match between the two components 5 9 External LNA Gain and Noise Figure The SL871 can be used with an external LNA such as what might be found in an active antenna Because of the internal LNA the overall gain including signal losses past the external LNA should not exceed 14 dB Levels higher than that can affect the jamming detection capability of the SL871 If a higher gain LNA is used either a resistive Pi or T attenuator can be inserted after the LNA to bring the gain down to 14 dB The external L
21. etely downloaded The receiver switches to the tracking engine to lower the power consumption when A valid GPS GNSS position is obtained The entire almanac has been downloaded The ephemeris for each satellite in view is valid Backup or Hibernate State In the backup or hibernate state the receiver is in the lowest current consuming mode The receiver operation is stopped only the backup supply V BAT is powered on while the main supply VCC can be switched off by the host Waking up from Backup State to Full Power can be controlled by the host by switching on the VCC supply or After waking up the receiver uses all available internal aiding including GNSS time Ephemeris and Last Position resulting in the fastest possible TTFF in either hot or warm start modes During Backup State the I O block is powered off The host should force its outputs to a low state or to a high Z state during the Backup State to minimize small leakage currents 10 WA typically at Standby State Standby Mode In this mode the receiver stops navigation the internal processor enters standby state and the current drain at main supply VCC is typically reduced to 0 4 mA Enter standby mode by sending the NMEA command PMTK161 0 28 The host can wake up the module from Standby mode to Full Power mode by sending any byte via the host port Periodic Mode This mode allows autonomous power on off with reduced fix rate to reduce average power consumpti
22. fail or malfunction Tip or Information Provides advice and suggestions that may be useful when integrating the module All dates are in ISO 8601 format i e YY Y Y MM DD Related Documents e SL871 Product Description 80434ST10610A gt e z A P b t Se KN E l T NA f N Let d K 2 i c Pa NES fe ra E bc F s NG MEM Z D Ult M K T bA hh y B EN d RUM E x TUUM E ation from Telit Communications S p A All Rights Reserved Page 8 of 35 elit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 e SL87 EVK User Guide 4 H Pn OO 2 A f f Jn A G F GI e a Fa m F odi ABI Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 9 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 2 Powering the SL871 The SL871 has three power supply pins VCC VBAT and VCC RF 2 1 3 0V Main Supply Voltage The VCC pin provides the main supply voltage When power is first applied the module will come up in a full power continuous operation mode During operation the current drawn by the module can vary by some orders of magnitude especially if enabling low power operation modes Any supply must be able to handle the current fluctuation including any in rush surge current GPS GNSS positioning modules req
23. ffect of making an RF short at LI at one end of the stub to appear as an RF open The RF short is created by the good quality RF capacitor operating at self resonance The choice between the two would be determined by e RF path loss introduced by either the inductor or quarter wave stub e Cost of the inductor e Space availability for the quarter wave stub Simulations done by Telit show the following e Murata LQGIS5HS27NJ02 Inductor 0 65 dB of additional signal loss e Quarter wave stub on FR4 0 59 dB of additional signal loss e Coilcraft BOOTJLC Inductor used in ref design 0 37 dB of additional signal loss This additional loss occurs after the LNA so it is generally not significant unless the circuit is being designed to work with either an active or a passive antenna 7 S AA a A a PP gt e L 1 2 p 54 d ri b TU L4 P Pm KIN i 5 4 SY i S LEAN sia NG ihi 8 Led STE A fa e MIX b s g 8 x LAME DN ZC lt s 1 i e i Jh i ps mm TE LAE 4 ta ke F Inm wu Hi e bh az e A 7 p i EJ e d wa MM ma 2 p Uis i nt M a T E Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 26 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 5 11 RF Interference RF Interference into the GNSS receiver tends to be the biggest problem
24. front end of a GNSS receiver For example antenna X has an antenna gain of 5 dBic at azimuth and an LNA gain of 20 dB for a combined total of 25 dB Antenna Y has an antenna gain of 5 dBiC at azimuth and an LNA gain of 30 dB for a combined total of 25 dB However in the system antenna X will outperform antenna Y by about 10 dB refer to Section 5 4 for more details on system noise floor An antenna with higher gain will generally outperform an antenna with lower gain Once the signals are above about 130 dBm for a particular satellite no improvement in performance would be gained However for those satellites that are below about 125 dBm a higher gain antenna would improve the gain and improve the performance of the GNSS receiver In the case of really weak signals a good antenna could mean the difference between being able to use a particular satellite signal or not ag gt E S e P R 4 f KZ d 1 f DMI Bs 7 r i 3 d p XL EK KE 28 Le e amp e E pi 1 j d b Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 18 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 9 4 System Noise Floor As mentioned earlier the SL871 will display a reported C No of 40 dB Hz for an input signal level of 130 dBm The C No number means the carrier or signal is 40 dB greater than the noise floor measured in a
25. igher levels The amplifier needs to stay in the linear region when presented with these other signals Again the system designer needs to determine all of the unintended signals and their possible levels that can be presented making sure the external LNA will not be driven into compression If this were to happen the GNSS signal itself would start to be attenuated and the GNSS performance would suffer an GER without written authorization from Telit Communications S p A All FA Reserved Page 25 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 5 10 Powering the External LNA active antenna The external LNA needs a source of power Many of the active antennas accept a 3 volt or 5 volt DC voltage that is impressed upon the RF signal line This voltage is not supplied by the SL871 but can be easily supplied by the host design Two approaches can be used The first 1s to use an inductor to tie directly to the RF trace This inductor should be at self resonance at L1 1 57542 GHz and should have good Q for low loss The higher the inductor Q the lower the loss will be The side of the inductor connecting to the antenna supply voltage should be bypassed to ground with a good quality RF capacitor again operating at self resonance at the L1 frequency The second approach is to use a quarter wave stub in place of the inductor The length of the stub is designed to be exactly a quarter wavelength which has the e
26. is chosen to be self resonant at the GNSS frequency such that is looks pretty close to an RF short at that frequency V ANT is the supply voltage for the external active antenna Pin 7 can be connected to VCC for compatibly issues or left unconnected TX is the normal digital output and as configured in the reference design is a serial UART with a default bit rate of 9600 bps 1 stop bit and 8 data bits This is a 1 8 volt logic level signal As is the case with all serial data the idle state is logic one RX is the normal digital input and as configured in the reference design is a serial UART with a default bit rate of 4800 bps 1 stop bit and 8 data bits This is a 1 8 volt logic level signal but is tolerant to 3 6 volts As is the case with all serial data the idle state is logic one d g j KI gt P b Um 4 7 f DMI Bs bA 3 7 it mp D au d a KE 28 O Lo e W e 2 TITE Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 28 of 35 lelit 51871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Be careful to tri state this line if the SL871 is turned off to avoid back driving the SL871 Firmware Configuration The SL871 can be configured by means of firmware in order to fit better into the overall system This section describes certain aspects of the receiver that can be configured 6 1 Low Power Modes The SL871 module can be o
27. is the Agilent design software AppCAD which can be downloaded for free As you can see using a typical FR4 board stack up the calculated Trace width for this board is 900 microns or approximately 35mill This may or may not be an acceptable trace width and board material may need to be adjusted accordingly 20u 10u Solder Resist Cu 35u 7u base Plating T LI PREREG 460u 45u Cu 35u t 7u CORE 500u 50u 60 10 Cu 35u 7u L3 PREREG 460u 45u L4 Cu 35u 7u base Plating 20u 10u Solder Resist Elect Length A Elect Length Dielectric amp r 4 6 1 0 Wavelength mil p z Vp fraction of c Frequency r5 cH v E eff Length Units WH Figure 1 Typical Board stack and calculated trace width lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 As 1s often the case board material may be dictated by other applications that are integrated onto the host board The board thickness may be such that a very narrow trace may result This may not be acceptable and can also lead to issues when the trace meets a component pad In situation like this the ground layer directly under the RF trace path can be removed and the RF ground is then moved to the next layer This can result in a more acceptable trace width CMPORC Lay Narrow traces and component met Lay pad mismatch pac divided vi a Wider trace width allowed
28. ite bead and bypass capacitor This supply voltage is not switched 2 4 Power management and operating modes The Telit SL871 offers a power optimized architecture with built in autonomous power saving functions to minimize power consumption at any given time The receiver operates in two modes Continuous mode for best performance or Power Save mode for optimized power consumption Power saving modes are listed below KA f E d 1 4 utt A A As e g R A 3 7 Ty em L EMMSAT iT A rig Gas g Eb c B Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 10 of 35 elit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Backup Mode Periodic mode Standby mode Always locate mode d E CS is g pa bs gt f G d IL s 8 p GI e WEISS Fa m F odi ABI Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 11 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 3 Power Modes 3 1 3 2 3 3 3 4 Continuous Mode The SL871 powers up directly into full power continuous state Continuous mode uses the acquisition engine at full performance resulting in the shortest possible TTFF and the highest sensitivity It searches for all possible satellites until the almanac is compl
29. ithout written authorization from Telit Communications S p A All Rights Reserved Page 3 of 35 lelit 51871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Usage and Disclosure Restrictions License Agreements The software described in this document is the property of Telit and its licensors It is furnished by express license agreement only and may be used only in accordance with the terms of such an agreement Copyrighted Materials Software and documentation are copyrighted materials Making unauthorized copies is prohibited by law No part of the software or documentation may be reproduced transmitted transcribed stored in a retrieval system or translated into any language or computer language in any form or by any means without prior written permission of Telit High Risk Materials Components units or third party products used in the product described herein are NOT fault tolerant and are NOT designed manufactured or intended for use as on line control equipment in the following hazardous environments requiring fail safe controls the operation of Nuclear Facilities Aircraft Navigation or Aircraft Communication Systems Air Traffic Control Life Support or Weapons Systems High Risk Activities Telit and its supplier s specifically disclaam any expressed or implied warranty of fitness for such High Risk Activities Trademarks TELIT and the Stylized T Logo are registered in Trademark Office All other p
30. m or less in open sky applications Note that only an SBAS can be used as source of differential corrections Other sources such as data from RTCM beacons are not supported By default the SL871 does not attempt to acquire SBAS satellites This can be changed by sending in a DGNSS Source and specifying the source of DGNSS corrections as SBAS When the receiver acquires SBAS satellites it will demodulate and use corrections data from the satellite signal The receiver can be configured to compute SBAS satellite range measurements and use them in the navigation solution This can be enabled software command 6 2 3 2 D Acquisition By default the SL871 will compute a 2 D solution when possible when performing initial acquisition In a 2 D solution the receiver assumes a value for altitude and uses it to estimate the horizontal position Under warm and hot start conditions the receiver uses the last known value of altitude which is a good assumption in most situations However under cold start conditions the last position is unknown and the receiver assumes a value of 0 In situations where the true altitude is significantly higher than that the horizontal position estimate will be noticeably impacted To accommodate applications for which these situations are a concern a version of SL871 firmware is offered that requires a calculated altitude 1 e a 3 D navigational solution in order for the receiver to first enter navigation S i
31. nimum of 130 dBm when the antenna 1s in the worst orientation and the satellite is 5 degrees or more above the horizon In actual practice the GNSS satellites are outputting slightly more power than specified by IS GNSS 200E and the signal level typically goes higher as the satellites have higher elevation angles The SL871 will display a reported C No of 40 dB Hz for a signal level of 130 dBm at the RF Input Reproduction GER without written authorization from Telit Communications S p A All Rights Reserved Page 16 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Each GNSS satellite presents its own signal to the SL871 and best performance is obtained when the signal levels are between 130dbm and 125dBm These received signal levels are determined by e GNSS satellite transmit power GNSS satellite elevation and azimuth Free space path loss Extraneous path loss such as rain Partial or total path blockage such as foliage or building Multipath caused by signal reflection GNSS antenna Signal path after the GNSS antenna The first three items in the list above are specified in IS GNSS 200E readily available multiple sources online IS GNSS 200E specifies a signal level minimum of 130 dBm will be presented to the receiver when using a linearly polarized antenna with 3 dBi gain The GNSS signal is relatively immune to rainfall attenuation and does not really need to be considered However the GN
32. on The main power supply VCC is still active but turning the supply on and off is controlled internally by NMEA commands Enter periodic mode by sending the following NMEA command PMTK225 Type Run time Sleep time 2nd run time 2nd sleep time checksum YN A ei AE ui d 4 d vi f E ez GET G i H e Hit Ki i d SET s e f b Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 12 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Where Type 1 for Periodic Backup mode e Run time Full Power period ms e Sleep time Standby Backup period ms e 2nd run time Full Power period ms for extended acquisition 1f GNSS acquisition fails during Run time e 2nd sleep time Standby Backup period ms for extended sleep if GNSS acquisition fails during Run time Example PMTK225 1 3000 12000 18000 72000 16 for periodic mode with 3 s navigation and 12 s sleep in backup state The acknowledgement response for the command is PMTK001 225 3 35 The module can exit Periodic mode by sending the command PMTK225 0 2B just after the module wakes up from a previous sleep cycle H MD c 7 L4 e d 4 F1 h ci fg D D L es P CN AA d Lg y d F d aoe hie Nas A r h T J A d ro la M E Reproduction forbidden wi
33. perated in one of four power management modes Full Power Standby Periodic and Always Locate can be selected depending upon the requirements of the system design regarding frequency of position updates and availability of GNSS signals in the operational environment The designer can choose a mode that provides the best trade off of performance versus power consumption Each of the power management modes can be commanded using the Serial commands which are available as part of the NEMA message set More details regarding low power operation can be found in the Software Application Note Gescht forbidden without written SNE from Telit Communications S p A All Rights Reserved Page 29 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 6 1 1 NMEA Protocol Considerations The SL871 positioning module includes a Universal Asynchronous Receiver Transmitter UART serial interface RxD TxD that supports configurable baud rates For information about the supported baud rates see the SLS7 Software User Guide including Protocol Specification The signal output and input levels are 0 V to VCC An interface based on RS232 standard levels 12 V can be implemented using level shifters such as Maxim MAX3232 Hardware handshake signals and synchronous operation are not supported 6 1 2 Static Navigation Static navigation also called position pinning is a mechanism that it is used by the receiver to freeze or pin
34. ringent performance expectations in hybrid navigation using signals from both GPS GLONASS Beidou GNSS systems 1 2 Audience This document is intended for helping customer with new product design using the Telit SL871 GNSS module or for those customers wanting to adopt existing designs to industry standard existing modules 1 3 Contact Information Support For general contact technical support to report documentation errors and to order manuals contact Telit Technical Support Center TTSC at TS EMEA telit com TS NORTHAMERICA telit com TS LATINAMERICA telit com TS APAC telit com Alternatively use http www telit com en products technical support center contact php For detailed information about where you can buy the Telit modules or for recommendations on accessories and components visit http www telit com To register for product news and announcements or for product questions contact Telit Technical Support Center TTSC Our aim is to make this guide as helpful as possible Keep us informed of your comments and suggestions for improvements Telit appreciates feedback from the users of our information d C f LN fe r Ut io Id RK ei E e EN d GUM i e KZ mod R d SA S Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 7 of 35 1 4 1 5 1 6 lelit SL871 Hardwar
35. roduct or service names are the property of their respective owners Copyright O Telit Communications S p A 2014 Sg D La si fk fg P d y m L4 7 f d yr m PEP FAS Y GD J ai 2 AA a Es per ER er Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 4 of 35 lelit 51871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Contents EE ei e Le tee E E 7 ES o0 i 7 ae UI 7 a Ae OM act MOR EEN 7 ie WO UTNE INE ON eZ aU lO EE 8 bo WE EENHEETEN 8 E Related DOCU TIG TES AA 8 2 MOMS MN TINS E ME E 10 Zo p SOV Mai UPO NONONG E 10 227 WIRT Te KU oup Te EE 10 29 WG dE ge Ee e e EE 10 ZA Power management and operating modes een 10 3 POWEE IOS E 12 d ch CONS MOOG E 12 3 2 Backup or Hibernate ol t ee NR 12 UO MOO E 12 OY EB ouupuI 12 3 9 Always locate Mode 14 CHE AAP 15 go 15 FD da 15 SC Te TE 15 EE FERONLENd DESIGN RR 16 Sal RFO Botella EE 16 5 2 E Antenna Polarization WE 18 Dror ONS AMENN OA ae E E E R E E E E 18 VST O FOO DERE RR 19 me Reproduction GER without written authorization from Telit Camipiunita lone S p A All Right
36. rom the JEDEC website http www jedec org CAUTION This bag contains MOISTURE SENSITIVE DEVICES If Blank see adjacent bar code label Calculated shelf life in sealed bag 12 months at 40 C and 90 relative humidity RH Peak package body temperature C If Blank see adjacent bar code label After bag is opened devices that will be subjected to reflow solder or other high temperature process must a Mounted within 168 hours of factory If Blank see adjacent bar code label conditions lt 30 C 60 b stored at s1096 RH Devices require bake before mounting if a Humidity Indicator Card is gt 1096 when read at 23 5 C b 3a or 3b not met 9 If baking is required devices may be baked for 48 hours at 125 5 C Note If device containers cannot be subjected to high temperature or shorter bake times are desired reference IPC JEDEC J STD 033 for bake procedure Bag Seal Date If Blank see adjacent bar code label Note Level and body temperature defined by IPC JEDEC J STD 020 Figure 5 Label for Moisture Sensitive Devices ae P B REM EE g Reproduction forbidden without written authorization from Telit Communications S p A All Rights Reserved Page 32 of 35 d cms lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 7 2 ESD The SL871 is an electrostatic discharge sensitive device and should be handled in accordance with JESD625 A requiremen
37. s Reserved Page 5 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 Do Acuvewvsreue Passive e E EE 19 2 ee EL RET 19 5 7 PCB stack and Iracelmpedance eene nnns 21 9 0 Implications of the Pre select SAW Eilier aaa 24 9 9 External LNA Gain andNosetoure aa 24 5 10 Powering the External LNA active antennal es 26 ee el HE UCT ER Eeer 27 9 12 SMELLING eresi r a adenine ABRA 27 re e AR e La EE 28 SHEET eg ele 29 6 1 1 NMEA Protocol Considerations EE 30 6 1 2 aC INV 1G GUO E 30 6 1 3 Velocity Dead Reckoning NEE 30 ba e le e E aic IEEE 31 6 2 1 BUB sU m 31 6 2 2 SID m MT 31 6 2 3 ed e NER ER 31 7 Handling and SOLU CHING EE 32 kl e d Ee ER EC 33 AA 33 Pte FSSC MOY FSG NCS RR um 33 OCB EC RT T 34 7 DOCUM NEHO EE 39 me Reproduction GER without written authorization from Telit Communications S p A All Rights Reserved Page 6 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 1 Introduction 1 1 Scope The Telit SL871 is an OEM GNSS 9 7 x 10 1 x 2 5 mm receiver module based on the Mediatek MT3333 chip that supports All in One GNSS hybrid navigation The Telit SL871 receiver provides extremely low power and very fast TTFF together with weak signal acquisition and tracking capability to meet even the most st
38. thout written authorization from Telit Communicatio la ns S p A All Rights Reserved Page 13 of 35 lelit SL871 Hardware User Guide 1VV0301147 Preliminary r0 2014 04 11 3 9 Always locate Mode AlwaysLocate is an intelligent controller of the Periodic mode the main power supply VCC is still active but supply is controlled internally by PMTK commands Depending on the environment and motion conditions the module can autonomously and adaptively adjust the parameters of the Periodic mode e g on off ratio and fix rate to achieve a balance in positioning accuracy and power consumption The average power drain can vary based on conditions typical average power is 7 mW Associated profiles are High and Low Speed Walking Outdoor Static and Indoor The module can control the embedded VCC power switch autonomously only after the SL871 is set to Periodic or to AlwaysLocate mode by a PMTK command Enter AlwaysLocate mode by sending the following NMEA command S PMTK225 lt mode gt lt checksum gt lt CR gt lt LF gt Where mode 9 for AlwaysLocate in Backup mode Example PMTK225 9 22 The acknowledgement response for the command is PMTK001 225 3 35 The user can exit low power modes to Full Power by sending NMEA command PMTK225 0 2B just after the module wakes up from its previous sleep cycle an forbidden without written authorization from Telit Communications S p LA All Rights Reserved Page 14 of 35
39. ts for Handling Electrostatic Discharge Sensitive ESDS Devices Although the SL871 is a module the expecting handling of the SL871 during assembly and test is identical to that of a semiconductor device Note JEDEC standards are available for free from the JEDEC website http www jedec org 7 3 Reflow The SL871 is compatible with lead free soldering processes as defined in IPC JEDEC J STD 020 The reflow profile must not exceed the profile given in IPC JEDEC J STD 020 Table 5 2 Classification Reflow Profiles Although IPC JEDEC J STD 020 allows for three reflows the assembly process for the SL871 uses one of those profiles Thus the SL871 is limited to two reflows Note JEDEC standards are available for free from the JEDEC website http www jedec org When reflowing a dual sided SMT board it 1s important to reflow the side containing the SL871 module last This prevents heavier components within the SL871 becoming dislodged if the solder reaches liquidus temperature while the module is inverted 7 4 Assembly Issues Due to the piezo electric components within the SL871 the component should be placed close to the end of the assembly process to minimize shock to the module During board singulation pay careful attention to unwanted vibrations and resonances introduced into the board assembly by the board router S a N A a PP gt e L 1 9 ER d k TU P s Pm KIN E A z DR m A
40. uire a stable power supply In selecting a strategy to achieve a clean and stable power supply any resistance in the VCC supply line can negatively influence performance Consider the following points All supplies should be within the rated requirements At the module input use low ESR capacitors that can deliver the required current charge for switching from backup mode to normal operation At the module input use low ESR capacitors that can deliver the required current charge for switching from backup mode to normal operation We recommend keeping the rail short and away from any noisy data lines or switching supplies etc Wide power lines and or even power planes are preferred 2 2 VBAT Backup Supply Voltage In case of a power failure on the module supply VBAT supplies power to the real time clock RTC and battery backed RAM BBRAM Use of valid time and the GNSS GNSS orbit data at startup will improve the GPS GNSS performance i e enables hot and warm starts If no backup battery is connected the module performs a cold start at power up If no battery backup is to be used connect this pin to the VCC supply 2 3 VCC RF Output Voltage The VCC RF output voltage can provide voltage and current to an external active antenna or external LNA provided they are the same voltage level as VCC main supply The VCC RF can supply a maximum of 100mA and must be limited externally The VCC RF pin is connected internally to the VCC pin through a ferr
41. when determining why the system performance is not meeting expectations As mentioned earlier the GNSS signals are at 130 dBm and lower If signal higher than this are presented to the receiver it can be overwhelmed The SL871 can reject up to 12 CW in band jamming signals but would still be affected by non CW signals The most common source of interference is digital noise This is created by the fast rise and fall times and high clock speeds of modern digital circuitry For example a popular netbook computer uses an Atom processor clocked at 1 6 GHz This is only 25 MHz away from the GNSS signal and depending upon temperature of the SAW filter can be within the passband of the GNSS receiver Because of the nature of the address and data lines this would be broadband digital noise at a relatively high level Such devices are required to adhere to a regulatory standard for emissions such as FCC Part 15 Subpart J Class B or CISPR 22 However these regulatory emission levels are far higher than the GNSS signal 9 12 Shielding Shielding the RF circuitry generally is ineffective because the interference is getting into the GNSS antenna itself the most sensitive portion of the RF path The antenna cannot be shielded because then it can t receive the GNSS signals There are two solutions one is to move the antenna away from the source of interference or the second is to shield the digital interference to prevent it from getting to the antenna
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