M10音频设计User Guide - Acme Systems srl
Contents
1. 0 005002 24 3 1 3 Echo arithmetic command essere 27 3 2 Audio parameters suggestion s l u u 28 3 2 1 Hardware audio channel 1 in handset application 28 3 2 2 Hardware audio channel 1 in hands free application 28 3 2 3 Hardware audio channel 2 in headset application 28 3 2 4 Hardware audio channel 2 in hands free application 28 GSM AUDIO UGD V1 1 2 QUECTE GSM Module Audio Design User Guide TABLE 1 TABLE 2 TABLE 3 TABLE 4 TABLE 5 TABLE 6 TABLE 7 TABLE 8 TABLE 9 Table Index RELATED DOCUMENTS certet ttt ttt ttt ttt tette tbt 6 TERMS AND ABBREVIATIONS ertet tette tette totos noti 6 TERMS EXPLANATION ettet tette tte aaa 7 AUDIO SIGNALS CONFIGURATION OF DIFFERENT 8 AT QAUDCH INTRODUCTION ettet ttt ttes 24 AT QMIC 24444 14141404000 24 AT CLVL INTRODUCTION cccsssssssessssssssscsssescssseessscsssecssssessesessucesssesssecssusessevassecesneesssees 25 AT QSIDET INTRODUCTION annassa 26 AT QECHO INTRODUCTION csssssssssssssssessssessssessssesssvessusesssesssuessssesssssssuessetessueessneessees2. 1 10000 SPL AAC p SPL XINGHUI p SPL SHENGGUANGXUN p Horizontal axis represents frequency longitudinal axis represents loudness whose unit is dB GSM_AUDIO_UGD_V1 1 20 QUECTE THD AAC p THD XINGHUI p THD SHENGGUANGXUN p GSM Module Audio Design User Guide XY Graph 1 Hz THD AAC p 100 00 19 79 THD AAC p 100 00 19 79 delta x y 0 00 0 00 Figure 18 SPK THD Horizontal axis represents frequency longitudinal axis represents distortion whose unit is In Figure 17 and Figure 18 the three colors represent three venders products After comprehensive comparison the green one performs the best and the blue one is second and the red one is the worst 2 5 MIC choice It is recommended to use an electret microphone with a sensitivity of 42 3dB Pa 2V not less than 44 3dB and impedance of 2 2k 2 If RF TDD noise is detected at the MIC please contact MIC vendor for product with better RF suppression capability Furthermore the microphone channel circuit can be optimized to decrease TDD problem at MIC side 2 6 Instruction of vehicle application 1 When the module is used in vehicle application and the hands free talking function is required audio channel 1 can be used Note that audio channel 1 can t provide ringing for in coming calling and SMS calling 2 Because the distance between the talker and the MIC is often farer high sen
3. SBRGER EQUENCY RESPONSE SB 99 4 20 FIGURERISEBSPK THD 218 95 68 99 MF eese 21 FIGURE 19 AUDIO CHANNELS INSIDE BB CHIP n ene 23 GSM AUDIO UGD V1 1 44 GSM Module Audio Design User Guide QUE IC 0 Revision History Description of change 2009 11 2 Tracy Zhang Initial 2010 12 31 1 Add AT command instructions in Figure19 2 Chang the back cover image GSM AUDIO UGD V1 1 5 GSM Module Audio Design User Guide QUECTE 1 Introduction This document provides reference design and advices about audio design of Quectel modules including peripheral circuits parameter setting PCB layout whole structure etc Understanding the details of this document would help customer on developing a good acoustic performance of product 1 1 Related documents Table 1 Related documents Document name Remark 1 Mxx HD Hardware design document Mxx refers to Quectel s GSM modules starting with M Mxx ATC AT commands set 1 2 Terms and abbreviations Table 2 Terms and abbreviations Description Audio Front End Base Band Direct Current Electro Static Discharge General Purpose Input Output GSM Global System for Mobile communications LDO Low Drop Out regulator MIx Quectel s GSM module starting with M1 such as M10 and M16 Non Linear Processing Power Amplifier Programmable Gain Amplifier Power Supply Rejection Ratio Radio Frequency SPK Spe
4. Audio Design GSM Module Audio Design User Guide QUE c Document Title GSM Module Audio Design User Guide Version 1 1 Date 2010 12 31 Status Release Document Control ID GSM AUDIO UGD VI 1 General Notes Quectel offers this information as a service to its customers to support application and engineering efforts that use the products designed by Quectel The information provided is based upon requirements specifically provided for Quectel by the customers Quectel has not undertaken any independent search for additional relevant information including any information that may be in the customer s possession Furthermore system validation of this product designed by Quectel within a larger electronic system remains the responsibility of the customer or the customer s system integrator All specifications supplied herein are subject to change Copyright This document contains proprietary technical information which is the property of Quectel Limited copying of this document and giving it to others and the using or communication of the contents thereof are forbidden without express authority Offenders are liable to the payment of damages All rights reserved in the event of grant of a patent or the registration of a utility model or design All specification supplied herein are subject to change without notice at any time Copyright Quectel Wireless Solutions Co Ltd 2010 GSM AUDIO UGD V1 1 1 GSM Modu
5. channels Usually customer need not modify any parameter But in case of some applications such as audio channel 1 being applied in hands free mode or failing to completely cancel echo caused by bad circuits or structure some of parameters can be modified to reduce more echo Advices of audio parameters in different application are provided in the next section 3 2 Audio parameters suggestion Audio parameters are recommended in this section according to customer common applications including hardware audio channel 1 in handset application and hands free application hardware audio channel 2 in headset application and hands free application The enumerative parameters of AT QMIC AT CLVL AT QSIDET can be changed by customer according to peripheral components performance The enumerative parameters of AT QECHO are not recommended to change 3 2 1 Whole structure AT QMIC AT CLVL Hardware audio channel 1 in handset application AT QSIDET AT QECHO 3 2 2 Good echo 0 4 60 80 221 1024 16388 849 0 Bad echo Whole structure AT QMIC AT CLVL Hardware audio channel 1 in hands free application AT QSIDET 221 1024 10756 849 0 AT QECHO Good echo 0 2 60 0 224 1024 5218 374 0 3 2 3 Bad echo 0 0 40 0 224 1024 2218 374 0 Whole structure AT QMIC AT CLVL Hardware audio channel 2 in headset application AT QSIDET AT QECH
6. 10pF 0603 capacitor here is for filtering out 1800MHz RF interference However the resonant frequency point of a capacitor largely depends on the material and production technique Therefore customer would have to discuss how to choose the most suitable capacitor with vendor for filtering GSM850MHz EGSM900MHz DCS1800MHz and PCS1900MHz separately The 33pF and 10pF values here are just for reference from Murata Company The severity degree of the RF interference in the voice channel during GSM transmitting period largely depends on the application design In most cases EGSM900 and GSM850 TDD noise are more severe while in some cases DCS1800 TDD and PCS1900 noise are more obvious Therefore customer should decide which capacitors to use based on test result Sometimes even no RF filtering capacitor mounted the TDD performance is still acceptable TVS components can protect microphone and receiver from ESD damage They should be laid as close as possible to audio device or audio interface The capacitor C135 4 7uF R302 1kQ and R308 1kQ in Figure 2 are used to suppress the voltage ripple between VMIC and AGND thus ensure a cleaner bias supply to the microphone 2 1 1 2 Hands free application of audio channel 1 If only hands free application is required in design the audio channel 1 is recommended to be AUDIO UGD V1 1 10 GSM Module Audio Design User Guide QUECTE used Because audio channel 1 supports differential
7. Before setting the sidetone gain level AT QAUDCH command must be used to specify a software audio channel The formats of read and write commands are shown in Table 8 Table 8 AT QSIDET introduction Read Command _ Response AT QSIDET QSIDET NORMAL_AUDIO lt gainlevel software channel0 gt OK QSIDET HEADSET_AUDIO lt gainlevel software channel 1 gt OK Write Command Response AT QSIDET lt g OK success ainlevel active ERROR fail software Parameter channel gt lt gainlevel active software channel gt int 0 255 Setting to 0 represents closing sidetone Reference AT QAUDCH 0 AT QSIDET 80 AT QSIDET Response QSIDET NORMAL_ AUDIO 80 OK The sidetone gain level should be set to a suitable value Too high level leads to local environmental noise too low level leads to uncomfortable talking feeling If customer needs to have a larger input voltage scale in MIC port for special applications such as DTMF tone transfer through MIC channel some other undocumented AT commands related with acoustic configuration can be utilized to support them Please contact Quectel for details of these commands GSM_AUDIO_UGD_V1 1 26 GSM Module Audio Design User Guide 3 1 3 AT QECHO is used to modify echo arithmetic parameters of all three software audio channels There are five parameters in this command The formats of read and write commands are shown in Table 9 Echo arithmetic command T
8. A ais j FBMH1608HM601 T 10p 33pF 100K FB301 j A aa I I U302 C311 c2 i C308 p ROS age I SPK2P a nc vo L5 or 33p F RS 20K 3 FB302 acm A ine ES La l 1 6 FBMH16088M601 T i SHUT_DOWN VDD I C312 C3 T j 5 i 2 a NE MK BYPASS GND 910 an 15 c20 OpF 33pF I 100K myz CDs GND2 i I 6310 j GNDS GND4 I I I I I GPIO_SHUTDOWN gt 33pF 6205 1 Close to speaker lt VBAT Figure 11 Hands free application of SPK2P with TPA6205A1 GSM_AUDIO_UGD_V1 1 15 GSM Module Audio Design User Guide QUE c lo I I l 10pF 33pF FBMH1608HM601 T 12 c15 FB1 j ocv T 4 I 1 I U301 ci i b I c5 100nF R2 20K 4 I SPK2P C IN vol LOpF SpF FB2 i 3 IN vo2 EVV 1 4 FBMH1608HM601 T 16 luF 2 2 7 i BYPASS VDD 10pF 33pF Y 1 7 I C6 T 14 GPIO SHUTDOWN 4 i SHD eno HA I I 10uF i 18 100 SpF R4 r VBAT Close to speaker Figure 12 Hands free application of SPK2P with LM4990 NCP2890 I I I i 10pF 33pF
9. i FBMH160SHM601 T od c60 E R18 4 FB11 100K PSA T 4 l I C56 c58 i I I 5 1 omm 1 SPR2P gt c53 E vol hopF lur FB12 j 1 FC1 2 aaa T 33pF C63 10uF FBME1608HM601 T I i C44 FC2 vec I M i 10pF 33pF Y h m GND c55 C59 I I I I I Close to speaker 8 6 c61 F K 341 10uF VBAT R19 10K 4 MC34119 SpF R20 1 7K BG1 GPIO SHUTDOWN K 100K lt VBAT Figure 13 Hands free application of SPK2P with MC34119 2 2 Methods to avoid TDD noise It is particularly important to avoid and reduce TDD noise in audio design of GSM system Except the ways mentioned above such as filter capacitors magnetic beads and differential traces other advices are provided below GSM_AUDIO_UGD_V1 1 16 GSM Module Audio Design User Guide 1 2 3 4 5 6 7 QUECTE It is strongly recommended to use an electret microphone with two filter capacitors 10pF 0603 and 33pF 0603 in handset and hands free application These two capacitors could largely suppress coupling TDD noise from RF interference Place the RF filter capacitors as close as possible to audio components or interfaces on PCB Audio traces should be as short as possible and firstly pass through the filter capacitors and then connect to other pins One terminal of RF filter capacitors can fully connect main
10. is shown as below SPK2P _ gt BLM15HD1025N1 FB5 2 lt __ BLM15HD1025N1 LGK2009 0201 TVS3 Close to headset connector Figure 9 Headset application of M20 audio channel 2 If the earphone inserting detection and answer key detection functions are required in GPIOO can be used to detect earphone inserting and ADCO can be used to detect pressing answer key The reference circuit is present as below GSM_AUDIO_UGD_V1 1 14 GSM Module Audio Design User Guide GPIOO HEADSET DETECT QUECTE R304 Ik 22uF Cl SPK2P gt BLM15HD102SN1 FB5 BLM15HD102SN1 LGK2009 0201 TVS3 Close to headset connector Figure 10 Headset application with earphone detection of M1x audio channel 2 M20 has internal detection circuit for earphone but associated components are not mounted in default hardware configuration The earphone detection is not supported in default firmware of M1x and M20 2 1 2 2 Hands free application of audio channel 2 When audio channel 2 is used for hands free application the MIC2P 2N circuit is same to MICIP IN and the trace principle in PCB should follow differential mode Since SPK2P signal is single ended the input circuit needs some modification compared to SPK1P 1N The reference circuit is recommended as below I I i I C313 a i issus x R313 100K x
11. 27 GSM_AUDIO_UGD_V1 1 3 GSM Module Audio Design User Guide ETE Figure Index FIGURE 1 HANDSET APPLICATION OF MIX AUDIO CHANNEL 1 a aaa 9 FIGURE 2 HANDSET APPLICATION OF M20 AUDIO CHANNEL 1 em 9 FIGURE 3 LDO CIRCUIT TO VMIC OF 20 2 2224004444 0 00 0000 10 FIGURE 4 HANDS FREE APPLICATION OF SPKIP IN WITH TPA6205A1 11 FIGURE 5 HANDS FREE APPLICATION OF SPK1P 1N WITH LM4990 NCP2890 12 FIGURE 6 HANDS FREE APPLICATION OF SPKIP IN WITH MC34119 12 FIGURE 7 SCHEMATIC DIAGRAM 13 FIGURE 8 HEADSET APPLICATION OF MIX AUDIO CHANNEL 2 ee 14 FIGURE 9 HEADSET APPLICATION OF M20 AUDIO CHANNEL 2 eee 14 FIGURE 10 HEADSET APPLICATION WITH EARPHONE DETECTION OF M1X AUDIO CHANNEL 2 pertenecer ee 15 FIGURE 11 HANDS FREE APPLICATION OF SPK2P WITH 6205 1 15 FIGURE 12 HANDS FREE APPLICATION OF SPK2P WITH LM4990 NCP2890 16 FIGURE 13 HANDS FREE APPLICATION OF SPK2P WITH MC34119 16 FIGURE 14 FIVE ECHQGJPATLIS 8 E W eene 18 FIGURE 15 MICROPHONE SOCKET DESIGN eere ren rennen rennen 18 FIGURE 16 SPEAKER SOCKET DESIGN ceses e e eese nennen nennen innen 19 FIGURE 17
12. DIO MAIN CHANNEL I I 1 4 I i 10135 2312 C35 E R303 pas H azur 1830 162 Tor 33 Chop 7 33 gt gt 10P 33P ci 4 Figure 2 Handset application of M20 audio channel 1 GSM_AUDIO_UGD_V1 1 receiver GSM Module Audio Design User Guide QUECTE The voltage input scope of MIC bias VMIC is 2 5V 3 3V To avoid interference customer had better use a separate LDO to supply for VMIC The recommended circuit of the LDO is shown as below U203 XC621 9B3021R 3 3V 6V Poal VMIC 1 600ohm 01008Hz VIN VOUT 1 gt 2 enp n C210 C205 p ada 2 Nc 100nF 4 TuF C209 4 TuF AGND 10nF IVA AGND ae AGND S i N Figure 3 LDO circuit to VMIC of M20 MICIP IN In order to supply a stable bias voltage for audio circuit of MIC the LDO component should be placed as close as possible to the audio circuit Ground signal of LDO output should be connected to analog ground AGND and separately laid trace to AGND pin of module interface The 33pF 0603 capacitors in Figure 1 and Figure 2 are applied for filtering out 900MHz RF interference when the module is transmitting at EGSM900MHz Without placing this capacitor in SPK signals TDD noise could be heard at the near end of the voice communication Similarly without the capacitor in MIC signals TDD noise could be heard at the far end Moreover the
13. IO_UGD_V1 1 12 GSM Module Audio Design User Guide Quecre of customer s host MCU 2 1 1 3 Advice for audio trace of channel 1 As the audio signals are very sensitive and are interfered easily from power supply ripple unbalanced ground and RF burst radiation the traces MICIP and MICIN SPK1P and SPKIN in the PCB should follow the layout principle of differential traces Moreover these two pairs of signals should be separated from each other by flooding ground to avoid echo interference from SPK signal to MIC signal An example is shown in Figure 7 Figure 7 Schematic diagram of audio trace 2 1 2 Audio channel 2 MIC2P 2N is differential signal while SPK2P is single end signal This channel can be applied to headset application or hands free application 2 1 2 1 Headset application of audio channel 2 Headset application circuit of M1x audio channel 2 is recommended as below GSM_AUDIO_UGD_V1 1 13 GSM Module Audio Design User Guide QUECTE 22uF C1 SPK2P BLM15HD102SN1 FB5 MIC2P lt BLM15HD1025N1 a TVS3 C9 10pF 33pF Close to headset connector Figure 8 Headset application of M1x audio channel 2 The capacitor 22uF in Figure 8 is used for DC block In M20 this capacitor is integrated in the SPK2P line within the module thus there is no need to add it in the external circuit The recommended circuit of headset application using M20 audio channel 2
14. O Good echo 1 9 30 144 221 1024 0 849 1 3 2 4 Bad echo 1 8 10 80 221 1024 16388 849 1 Whole structure AT QMIC AT CLVL Hardware audio channel 2 in hands free application AT QSIDET AT QECHO Good echo 2 8 35 0 224 1024 5218 374 2 Bad echo 20 0 2 7 GSM_AUDIO_UGD_V1 1 224 1024 2218 374 2 28
15. able 9 AT QECHO introduction Read Command AT QECHO Write Command AT QECHO lt control word gt lt NLP gt lt echo suppression gt lt noise reduction gt lt channel gt Reference Default parameters of three channels Response QUECTE QECHO lt control word gt lt NLP gt lt echo suppression gt lt noise reduction gt lt channel gt OK Response OK ERROR Parameters lt control word gt lt echo suppression gt lt noise reduction gt lt channel gt success fail 221 in handset or headset application 224 in hands free application 0 represents disabling the whole echo arithmetic int 0 2048 The greater the value the more reduction of echo 0 means disabling the NLP algorithm int 0 32767 The smaller the value the more reduction of echo 0 means disabling the echo suppression algorithm The default value of software channel 1 is 0 because headset application no need to use echo suppression 849 in handset or headset application 374 in hands free application 0 Software channel 0 1 Software channel 1 2 Software channel 2 AT QECHO 221 1024 16388 849 0 AT QECHO Response QECHO 221 1024 16388 849 0 OK GSM_AUDIO_UGD_V1 1 QECHO 221 1024 16388 849 0 AT QECHO 221 1024 0 849 1 QECHO 224 1024 5218 374 2 Quectel modules configure the best default parameters of this command to all three software 27 GSM Module Audio Design User Guide QUECTE
16. aker TDD Time Division Duplex THD Total Harmonic Distortion TVS Transient Voltage Suppressor GSM AUDIO UGD 1 1 6 GSM Module Audio Design User Guide QUECTE 1 3 Terms explanation Table 3 Terms explanation Echo Cancellation Echo Suppression TDD noise Explanation In talking mode the far end could hear its own voice returned from the module side the near end with a delay of about several hundreds of milliseconds It can be caused at the near end by various reasons such as voice at the receiving circuit coupling to the microphone circuit due to improper circuit unsealed mechanical structure very loud voice from receiver or speaker getting into microphone high sensitivity microphone Talking quality can be obviously affected when echo problem is present A software arithmetic for canceling echo usually using in handset mode and headset mode A software arithmetic for suppressing echo usually using in hands free application Echo Suppression can reduce severe echo but it leads to half duplex or weakening to voice at the extent decided by the acoustic parameter settings GSM module generates an RF burst transmission lasting for 576us in every 4 615ms during voice communication which leads to higher power consumption at this 576us When the RF radiation energy conducts to the acoustic circuit the envelope curve of the RF burst could be present due to filtering effect and form a noise in the acoustic circuit
17. and not from leak of chassis interior Certain air space room should be reserved in the front cavity of microphone as it is necessary for good microphone performance Recommended design of speaker socket is shown as in Figure 16 Speaker Rubber gasket SS EFA WL Z Rear cavity Leak hole Figure 16 Speaker socket design A good way to suppressing the internal echo path is to sealing the rear cavity of receiver which is usually expensive The rear cavity of receiver and speaker is important for good voice quality A sealed rear cavity with sufficient space could produce a good voice output An 8Q speaker is often big and difficult to give an independently sealed rear cavity for it However sealing microphone socket in chassis is always useful Furthermore the whole chassis must be sealed as far as possible If there is any unavoidable leak hole keep it far away from microphone If the leak hole is close to microphone the voice coming from the hole could be picked up by MIC and then leads to echo at the far end If the leak hole is close to speaker the output voice quality could be aggravated at certain extent Direct air path This path can be obstructed through adjusting the holes direction and distance of receiver SPK and MIC For the purpose to transfer voice from receiver and SPK into MIC as little as possible the receiver or SPK and MIC should be installed
18. e internal DC MIC bias external DC MIC bias circuit must be added in customer host board 2 1 1 1 Handset application of audio channel 1 Handset application circuit of M1x audio channel 1 is recommended as below GSM AUDIO UGD 1 1 8 GSM Module Audio Design User Guide QUECTE hondset connector micophone l l l 1 UL 1 C1 E T I C312 esa ox lt ex I i 0 We w 10P 33P 10 aa amp ZEE 33P J301 i L 1 MICIN lt 4 i reece NS E 2 _ 1 T i c304 e305 TOP 33P Br 3 7 e308 _ 303 5 I P a E I 1 SPKIN 10 19 33 l l l I AY amp 1 l p l gt I close to handset connector I a AUDIO MAIN CHANNEL Figure 1 Handset application of M1x audio channel 1 Handset application circuit of M20 audio channel is recommended as below VMIC 2 2 5V 3 3V 01 i 33P I DI Mice lt y I 1 MICIN CC A I 11 spK1P Gap receiver 212304 2505 OP 33P pa 10 C306 leso c308_le3o9 33P DI T 1 to hondset connector AU
19. er Guide 10pF 33pF A FBMH1608HM601 T R6 100K EVV SPKIP gt a A i J3 SPKIN 11 L E I 10pF S3pF i GPIO SHUTDOWN E cio I I A s l LR Close to speaker 7 L C C CJ var Figure 5 Hands free application of with LM4990 NCP2890 g pp LM4990 from NATIONAL SEMICONDUCTOP NCP2890 from ON SEMICONDUCTOR AA BH I _ I l I i 10pF i FBMH1608HM601 T e T Co T i TE ow E 4 I 1 c46 C18 i I a SPKIP 10008 5 20K iN v i s I LOpF B3pF 2 R11 onc 1 225 c42 100nF 20K 3 FOI wa 8 I 1 1 10uF FBME1608HM601 T I FC2 voc amp 7 on 7 I 10pF 33pF y Y I exp cel RE C19 i RIS 10k MC34119 10uF L BSpF 1 I i R14 1 TK BGS ubi ee n Sa GPIO SHUTDOWN gt E Close to speaker R15 le L a y js cO oO VBAT 100K Figure 6 Hands free application of SPK1P IN with MC34119 MC34119 from FREESCALE SEMICONDUCTOR Inall kinds of audio PA chips customer should choose a model providing a greater PSRR value at 217Hz TPA6205A 1 is strongly recommended The pin named GPIO_SHUTDOWN in Figure 4 6 can be connected and controlled by an I O port GSM_AUD
20. far away from each other And their holes direction should not be opened in the same plane Customer can refer to the structure of SIEMENS desk phone whose hands free SPK opening hole locates in left center and MIC opening hole locates in back right bottom corner Nonetheless the voice from an 8Q speaker in hands free mode is so big that it can always be picked up by the microphone The echo arithmetic in software must be used to suppress this echo GSM_AUDIO_UGD_V1 1 19 GSM Module Audio Design User Guide 2 4 SPK choice QUECTE A SPK and receiver with higher sensitivity flatter frequency response less THD and impedance of 32 Q receiver 16 Q receiver or 8 Q speaker is recommended These technical data are often shown in data sheet of SPK and receiver For SPK its frequency response and THD performance can be tested by speaker test system SPK frequency and THD response are shown in Figure 17 and Figure 18 110 XY Graph 1 105 100 95 30 85 80 75 dB re 20 0 uPa 70 65 60 55 50 45 1 100 0 Baper TB re 20 0 JY y am C pru 1 1000 Hz SPL AAC 100 00 57 59 SPL AAC p 100 00 57 59 delta x y 0 00 0 00 Figure 17 SPK frequency response
21. ground of system Flood ground area as large as possible to reduce the ground impedance and improve ground integrality Reduce power voltage ripple especially the power supply in audio circuits Customer should use a wide trace from power source like adapter interface battery connector or LDO output pin to audio power supply Good antenna matching is also important to reduce power ripple In external audio circuits on customer host board the filtering capacitors and ESD protection devices should be connected to main digital ground and other audio components should use AGND from the module interface Please be noted that the AGND pin should not be connected with main digital ground in host board or else it could lead to TDD noise In order to reduce coupling interference place the GSM antenna as far as possible away from audio components and traces Microphone is most sensitive part to RF burst radiation Even a high quality microphone should be placed at least 5cm away from the antenna Do not make VBAT trace and audio traces parallel and lay VBAT trace as far as possible away from audio traces 2 3 Suppress echo in mechanical design It is important to consider how to suppress echo in the equipment with hands free function or in an application which microphone and speaker are very close to each other The mechanical design has significant impact on echo problem If it is not properly designed the echo suppressing arithmetic in s
22. le Audio Design User Guide EET Contents 5 RM 6 1 1 Related 6 1 2 Terms and abbreviations oie cacas 6 1 3 Terms explanation uu Sasa E San he een ena 7 2 Audio Hardware Design esccesccesccesecesecesecesecseceseceseceseceseceaeceaeceaeceaeceaeceseceaeceaeceaeseaeseaeeeaeeeaeees 8 2 1 Peripheral circuits recommended eene enne 8 2 1 1 Audi channel T 8 2 1 2 Audio channel 2 13 2 2 Methods to avoid TDD notse 0W67_ D Wh 16 2 3 Suppress echo in mechanical design 17 2 4 SPK choice 9 95 99 essent AT 20 2 5 MIC choice 4 Bf m DB Dee 21 2 6 Instruction of vehicle application a nennen 21 3 Audio Parameters Introduction and Suggestion a 23 3 1 Audio paramete Itroduction 6 h WA WB 24 3 118 Change active software channel 24 SNP Change audio gain 1 1 24120020000044 00000 0
23. like a constant pulse at 217Hz and its harmonic frequencies Another cause of the TDD noise is from the power supply The burst consumption of current can cause obvious ripple at the supply voltage at 217Hz If the ripple at the supply voltage conducts to audio circuit through power supply or ground TDD noise could be heard at the far end or the near end GSM AUDIO UGD V1 1 7 GSM Module Audio Design User Guide QUE Ic 2 Audio Hardware Design This chapter introduces some audio peripheral circuits including handset mode application with audio channel 1 hands free mode application with audio channel 1 headset application mode with audio channel 2 hands free application with audio channel 2 Moreover some ways to suppressing TDD noise and reducing echo are expatiated Table 4 Audio signals configuration of different models Audio channel 1 Audio channel 2 AIN1 AOUT1 AIN2 AOUT2 SPKIP IN MIC2P 2N SPK2P Differential Differential Differential Single end internal bias internal bias Differential Differential Differential i i Single end external bias internal bias 2 1 Peripheral circuits recommended 2 1 1 Audio channel 1 MICIP IN SPKIP IN are differential signals and this channel can be applied to handset application or hands free application There is a little difference in MICIP IN circuit between MIx and M20 Because M20 does not provid
24. oftware could not make up large echo caused by bad mechanical structure and even force to redesign Echo problem could be generated by several paths as shown in Figure 14 GSM AUDIO UGD 1 1 17 GSM Module Audio Design User Guide QUE c ENNIO A RO P Sc ee direct air path vibrations through casewofk internal air path vibrations through PCB distant echoes Figure 14 Five echo paths In these five paths internal air path and direct air path are the two most influential factors Other three factors vibrations through casework vibrations through PCB distant echoes are secondary Some suggestions about how to obstruct direct air path and internal air path are listed as follows 1 Internal air path Separating microphone from internal space of chassis by foam or rubber ring can effectively suppress the inner echo interference Recommended design of microphone socket is shown in Figure 15 Exit Hole Crust Figure 15 Microphone socket design GSM_AUDIO_UGD_V1 1 18 GSM Module Audio Design User Guide 2 QUECTE The best installation way of microphone socket is that encase microphone by silicone cover except for front cavity and design a cylindrical hole whose center is the exit hole inside the chassis make the microphone with silicone cover just fit the cylindrical hole so as to only let voice enter into microphone from the exit hole
25. output it would be helpful to suppress common mode noise in the audio output channel Please be noted that audio channel 1 does not provides ringing function for in coming voice or SMS calling To support ringing function audio channel 2 must be used The recommended MIC circuit of hands free application of audio channel 1 is the same as handset application M1x doesn t need external MIC bias circuit while M20 needs it as shown in Figure 2 The recommended circuits of SPK1P 1N output part in hands free application are shown in below 100nF 5908 1 SPK1P AND SPK1N DIFFERENTIAL LAYOUT GPIO SHUTDOWN gt Here is U302 TPA6205A1 from TEXAS INSTRUMENTS which is a audio power amplifier 1 100nF RS09__ 20 L C310 100K Figure 4 Hands free application of SPKIP IN with TPA6205A1 device and can driver a 8 9 speaker impedance GSM AUDIO UGD V1 1 11 I rm l o cs13 RES I R313 100K E DE 2 y FBMH1608FM601 T 33pF 2 100K FB301 l R14 100 ES LII l 4 U302 C3il c2 IN vo 1008 SSpF M FB302 1 Int vo T 1 1 1 l 1 6 FBMH1608HM601 T l SHUT DOWN VDD T cs12 SS gt 5 i BYPASS NDS 11 1 10 33pF ei I 13 003 12 GND5 HO f es 1 I 1 a 1304 GSM Module Audio Design Us
26. presents activating hardware audio channel 1 setting to 1 or 2 represents activating hardware audio channel 2 The formats of read and write commands are shown in Table 5 Table 5 AT QAUDCH introduction Read Command Response AT QAUDCH QAUDCH lt active channel gt Write Command AT QAUDCH success active channel Cfail gt Parameter lt active channel gt 0 Software channel 0 default 1 Software channel 1 2 Software channel 2 Reference HFQAUDCH 1 t QAUDCH Response QAUDCH 1 OK 3 1 2 Change audio gain level 3 1 2 1 Change microphone gain level AT QMIC is used to modify microphone uplink analog gain level All the three software channels can be set by this command The formats of read and write commands are shown in Table 6 Table 6 AT QMIC introduction Read Command _ Response AT QMIC QMIC lt gainlevel software channel 0 gt lt gainlevel software channel 1 gt lt gainlevel software channel 2 gt GSM_AUDIO_UGD_V1 1 24 GSM Module Audio Design User Guide QUE C Write Command Response AT QMIC OK success lt channel gt ERROR fail lt gainlevel gt Parameters lt channel gt 0 Software channel 0 1 Software channel 1 2 Software channel 2 gainlevel gt int 0 15 Reference OMIC 0 4 1 9 FQMIC 2 8 FQMIC ponse QMC 4 9 8 OK Customer should be flexible to set MIC gain level according to different sensi
27. sitivity MIC such as 38dB is recommended AUDIO UGD 1 1 21 GSM Module Audio Design User Guide QUECTE 3 Follow those previous instructions on suppressing echo problem Quectel module can run echo cancellation and echo suppression arithmetic simultaneously so that echo can be largely weakened and talking quality is still excellent even in hands free module In addition the uplink auto gain controlling mechanism of module efficiently restrains voice clipping at the MIC channel which is extremely useful for hands free mode The downlink noise reduction controlling mechanism is available to reduce environmental noise in the SPK output path which enhances comfortable feeling to the listener The next chapter is going to introduce how to set audio parameters in different applications Vehicle application is regarded as an example with bad and severe echo problem GSM_AUDIO_UGD_V1 1 22 GSM Module Audio Design User Guide QUE IC 3 Audio Parameters Introduction and Suggestion Audio channels of Quectel modules can be divided into audio channel 1 and audio channel 2 in hardware while it is defined three channels in software including software channel 0 software channel 1 and software channel 2 Software channel 0 is only applied in hardware channel 1 while both software channel 1 and software channel 2 can be applied in hardware channel 2 When hardware audio channel 2 is used for headset application software channel 1 mus
28. t be active for this hardware channel When hardware audio channel 2 is used for hands free application software channel 2 should be active for it and this configuration means two more gains added to the uplink and downlink of hardware audio channel 2 These two gains are constant in software But software channel 1 has no such gains Thus software channel 2 is designed for hands free application of hardware channel 2 Sketch map of audio channels inside BB chip of module is shown below AT QAUDCH ormal AT AUDG e Up link MIC 4 EL AT QECHO Inside BB chip normal Loud speaker AT QAUDCH AT CLVL speaker2 Down link headset I Figure 19 Audio channels inside BB chip PGA1 Programmable analog gain amplifier on microphone channel PGA2 Programmable analog gain amplifier on speaker channel in hardware audio channel 1 PGA3 Programmable digital gain amplifier on microphone channel PGA4 Programmable digital gain amplifier on speaker channel PGAS5 Programmable digital gain amplifier on sidetone PGA6 Programmable analog gain amplifier on speaker channel in hardware audio channel 2 GSM_AUDIO_UGD_V1 1 23 GSM Module Audio Design User Guide QUE IC 3 1 Audio parameters introduction This section will introduce common audio parameters which can be modified by AT commands 3 1 1 Change active software channel AT QAUDCH is used to set active software channel Setting to 0 re
29. tivity of microphones used For high sensitivity MIC gain level can be reduced for low sensitivity MIC gain level can be increased 3 1 2 2 Change speaker gain level AT CLVL is used to modify speaker downlink analog gain level of active software channel the three software channels can be set by this command Before setting the speaker gain level AT QAUDCH command must be used firstly to specify a software audio channel The formats of read and write commands are shown in Table 7 Table 7 AT CLVL introduction Read Command Response AT CLVL CLVL lt gainlevel active software channel gt OK Write Command Response AT CLVL lt gai OK Csuccess nlevel active ERROR fail software Parameter channel gt lt gainlevel active software channel gt int 0 100 Setting to 0 represents mute volume Reference AT QAUDCH 0 AT CLVL 50 AT CLVL Response GSM_AUDIO_UGD_V1 1 25 GSM Module Audio Design User Guide QUE IC CLVL 50 OK Customer can set speaker gain level according to different loudness of speaker used 3 1 2 3 Change sidetone gain level AT QSIDET is used to modify sidetone gain level of active software channel The software channel 0 and software channel 1 can be set by this command Sidetone gain must be closed in hands free application so the command is not supported in software channel 2 Note that when hardware audio channel 1 is applied to hands free please close the sidetone
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