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GSM/GPRS Modules

GSM Module Audio Design Guide

GSM Module Audo Design Guide Confidential/Release

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Audio Circuit Design

M1x and M95 have two hardware audio channels except M80. Three audio channels are defined in
software. AT+QAUDCH is used to read and set the software audio channel. This chapter provides audio
interface circuit and some solutions to resolve TDD noise and ECHO issues.

Table 1

：

Audio Hardware Configuration

Module

(AIN1/AOUT1)

(AIN2/AOUT2)

AOUT3

MIC

SPK

MIC

SPK

SPK

M1x

Differential

&

Internal Bias

Differential

Differential

&

Internal Bias

Signal-end

/

M95

Differential

&

Internal Bias

Differential

Differential

&

Internal Bias

Differential

/

M80

Differential

&

Internal Bias

Differential

Differential

&

Internal Bias

Signal-end

Differential

1. M95 module has built-in class AB amplifier and also supports voice and ringtone at channel AOUT2.
2. M80 module supports voice and ringtone at channel AOUT2. AOUT1 and AOUT3 can also output

ringtone but via AT+QRCH=1(only used at M80).

3. M80 module has built-in class AB amplifier at channel AOUT3, and the maximum power is 800mW.

Notes

Quectel

Confidential

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Summary of Contents for GPRS Series

Page 1: ...GSM Module Audio Design Guide GSM GPRS Series Version GSM_Module _Audio_Design_Guide_V3 0 Date 2013 05 24 www quectel com ...

Page 2: ...IS BASED UPON CUSTOMERS REQUIREMENTS QUECTEL MAKES EVERY EFFORT TO ENSURE THE QUALITY OF THE INFORMATION IT MAKES AVAILABLE QUECTEL DOES NOT MAKE ANY WARRANTY AS TO THE INFORMATION CONTAINED HEREIN AND DOES NOT ACCEPT ANY LIABILITY FOR ANY INJURY LOSS OR DAMAGE OF ANY KIND INCURRED BY USE OF OR RELIANCE UPON THE INFORMATION ALL INFORMATION SUPPLIED HEREIN ARE SUBJECT TO CHANGE WITHOUT PRIOR NOTICE...

Page 3: ... 2009 11 02 Tracy Zhang Initial version 1 1 2009 11 20 Tracy Zhang 1 Added some acronym 2 Added a Audio Power Amplitude manufacturer 3 Added a solution to TDD noise 4 Modified cover 1 2 2010 11 20 Roy Chen 1 Added a diagram of audio channel 3 0 2013 05 24 Jerry You 1 Added reference design of audio circuit M1x M95 M80 2 Added AT command AT QAPS Quectel Confidential ...

Page 4: ...ence Circuit 14 2 1 3 3 SPK Reference Circuit 15 2 1 4 M80 16 2 1 4 1 Microphone Reference Circuit 16 2 1 4 2 Receiver Reference Circuit 16 2 1 4 3 Headset Reference Circuit 18 2 1 4 4 SPK Reference Circuit 18 2 2 Ringtone 19 2 3 Hands free Application at Channel AIN1 AOUT1 20 2 4 Suggestion for Audio Layout 21 2 5 TDD Noise Solution 21 2 6 Suggestion for Mechanical Design 22 2 7 Component of SPK ...

Page 5: ...GSM GPRS Modules GSM Module Audio Design Guide GSM Module Audo Design Guide Confidential Release 4 35 4 Appendix A 35 Quectel Confidential ...

Page 6: ...dule Audio Design Guide GSM Module Audo Design Guide Confidential Release 5 35 Table Index TABLE 1 AUDIO HARDWARE CONFIGURATION 9 TABLE 2 REFERENCE DOCUMENT 35 TABLE 3 DESCRIPTION OF ECHO AND TDD NOISE 35 Quectel Confidential ...

Page 7: ...E CIRCUIT FOR AIN1 AIN2 13 FIGURE 8 RECEIVER REFERENCE CIRCUIT FOR AOUT1 14 FIGURE 9 HEADSET REFERENCE CIRCUIT 14 FIGURE 10 SPK REFERENCE CIRCUIT 15 FIGURE 11 MICROPHONE REFERENCE CIRCUIT FOR AIN1 AIN2 16 FIGURE 12 RECEIVER REFERENCE CIRCUIT FOR AOUT1 16 FIGURE 13 SPK REFERENCE CIRCUIT FOR AOUT2 17 FIGURE 14 SPK REFERENCE CIRCUIT WITH AUDIO POWER AMPLIFIER FOR AOUT2 17 FIGURE 15 HEADSET REFERENCE ...

Page 8: ...ailure to comply with these precautions Full attention must be given to driving at all times in order to reduce the risk of an accident Using a mobie while driving even with a handsfree kit cause distraction and can lead to an accident You must comply with laws and regulations restricting the use of wireless devices while driving Switch off the cellular terminal or mobile before boarding an aircra...

Page 9: ...a service area with adequate cellular signal strength Your cellular terminal or mobile contains a transmitter and receiver When it is ON it receives and transmits radio frequency energy RF interference can occur if it is used close to TV set radio computer or other electric equipment In locations with potencially explosive atmospheres obey all posted signs to turn off wireless devices such as your...

Page 10: ...N2 AOUT2 AOUT3 MIC SPK MIC SPK SPK M1x Differential Internal Bias Differential Differential Internal Bias Signal end M95 Differential Internal Bias Differential Differential Internal Bias Differential M80 Differential Internal Bias Differential Differential Internal Bias Signal end Differential 1 M95 module has built in class AB amplifier and also supports voice and ringtone at channel AOUT2 2 M80...

Page 11: ...erence circuit is shown as below 10pF 33pF 33pF 33pF Close to Microphone MICxP MICxN Differential layout Electret Microphone GND GND 10pF 10pF ESD ESD Module Figure 1 Microphone Reference Circuit for AIN1 AIN2 1 To avoid TDD noise issue during voice capacitors is recommended to add close to microphone and SPK 2 TVS components are used to protect microphone and receiver from ESD damage It has to cl...

Page 12: ... Differential layout 10pF 10pF 33pF 33pF 33pF Close to speaker GND GND 10pF Module ESD ESD Figure 2 Receiver Reference Circuit for AOUT1 SPK1P SPK1N Differential layout Amplifier circuit 10pF 10pF 33pF 33pF 33pF Close to speaker GND GND 10pF Module ESD ESD Figure 3 Receiver Reference Circuit with Audio Power Amplifier for AOUT1 Quectel Confidential ...

Page 13: ...r GND Module 22uF ESD Figure 4 SPK Reference Circuit for AOUT2 Module SPK2P AGND Differential layout Amplifier circuit 10pF 10pF 33pF 33pF Close to speaker GND GND C2 C1 ESD ESD Figure 5 Receiver Reference Circuit with Audio Power Amplifier for AOUT2 For the value of C1 and C2 please refer to input impedance of audio power amplifier Note Quectel Confidential ...

Page 14: ...33pF GND 10pF ESD Figure 6 Headset Reference Circuit 2 1 2 M95 2 1 3 Microphone Reference Circuit M95 module provides electrets microphone bias voltage for AIN1 and AIN2 Reference circuit for microphone is shown as bellow MICxP Differential layout Module 10pF 33pF 33pF 33pF Electret Microphone GND GND 10pF 10pF ESD ESD 33pF 10pF Close to Module MICxN GND GND GND GND 10pF 33pF 33pF 10pF Close to MI...

Page 15: ... 10pF ESD ESD Module Close to Receiver GND Figure 8 Receiver Reference Circuit for AOUT1 2 1 3 2 Headset Reference Circuit 1 2 4 3 Amphenol 9001 8905 050 MIC2P 22uF 68R 33pF GND AGND Close to Socket 33pF AGND 33pF 10pF GND Module 4 7uF LOUDSPKP Close to Module GND GND GND GND 10pF 33pF 33pF 10pF Differential layout 33pF 10pF MIC2N 0R ESD ESD Figure 9 Headset Reference Circuit Quectel Confidential ...

Page 16: ...odule Audo Design Guide Confidential Release 15 35 2 1 3 3 SPK Reference Circuit LOUDSPKN ESD ESD 0R 0R LOUDSPKP 8 ohm Module GND Close to Speaker 10pF 33pF 33pF 10pF 10pF 33pF GND Differential layout Figure 10 SPK Reference Circuit Quectel Confidential ...

Page 17: ... for microphone is illustrated as following figure 10pF 33pF 33pF 33pF Close to Microphone MICxP MICxN Differential layout Module Electret Microphone GND GND 10pF 10pF ESD ESD Figure 11 Microphone Reference Circuit for AIN1 AIN2 2 1 4 2 Receiver Reference Circuit SPK1P SPK1N Differential layout 10pF 10pF 33pF 33pF 33pF Close to speaker GND 10pF ESD ESD Module GND Figure 12 Receiver Reference Circu...

Page 18: ...ND Figure 13 SPK Reference Circuit for AOUT2 SPK2P AGND Differential layout Amplifier circuit 10pF 10pF 33pF 33pF Close to speaker ESD ESD Module C2 C1 GND GND Figure 14 SPK Reference Circuit with audio power amplifier for AOUT2 TPA6205A1 from TEXAS INSTRUMENTS is recommended which is a audio power amplifier device and can driver a 8Ω speaker impedance Note Quectel Confidential ...

Page 19: ... 8905 050 SPK2P MIC2N MIC2P 22uF 68R 33pF GND AGND Close to Socket Differential layout 33pF AGND 33pF 10pF GND Module 4 7uF ESD ESD Figure 15 Headset Reference Circuit 2 1 4 4 SPK Reference Circuit LOUDSPKP LOUDSPKN Differential layout 10pF 10pF 33pF 33pF Close to speaker GND 100pF ESD Module 0R 0R ESD GND Figure 16 SPK Reference Circuit Quectel Confidential ...

Page 20: ...T1 but support to output ringtone via channel AOUT2 M95 outputs ringtone via channel AOUT2 by default M80 outputs ringtone via channel AOUT2 by default channel AOUT1 can output ringtone via AT QAUDCH 0 and AT QRCH 1 Please refer to AT command description for detailed information about AT QRCH Parameter AT QRCH Test Command AT QRCH Response QRCH 0 1 OK Read Command AT QRCH Response QRCH n OK Write ...

Page 21: ... mode noise SPK circuit is recommended as following IN IN SHUT_DOWN BYPASS VO VO GND VDD C312 10pF C311 10pF 10pF C313 C4 33pF C2 33pF C3 33pF VBAT FB301 FB302 Close to speaker C19 10uF C20 33uF 5 8 SPK1N SPK1P C308 C309 100nF 100nF R308 R309 20K 20K R310 100K C310 220nF R313 100K R314 100K GPIO_SHUTDOWN 4 3 1 2 6 7 Figure 17 Hands free Reference Circuit at Channel AIN1 AOUT1 GPIO_SHUTDOWN is cont...

Page 22: ... Figure 18 shows an example Figure 18 Layout of Audio 2 5 TDD Noise Solution It is important to avoid or reduce TDD noise in audio circuit design and layout This chapter provides some solution to resolve it 1 It is strongly recommended to add an electrets microphone within two capacitors 10pF and 33pF in handset and hands free application These two capacitors could largely suppress coupling TDD no...

Page 23: ... at PCB or else it could lead to TDD noise 6 Antenna must be stay away from audio components and layout of audio circuit Keep the distance at least 5cm from antenna to microphone 7 Layout of power supply must be stay away from audio and cannot be parallel 2 6 Suggestion for Mechanical Design It is important to consider how to suppress echo in the equipment with hands free function or in an applica...

Page 24: ...press the inner echo interference Figure 20 shows recommended design for microphone socket Figure 20 Microphone Socket Design The best installation way of microphone socket is to 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 onl...

Page 25: ...with sufficient space could produce a good voice output An 8Ω 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 comin...

Page 26: ... of 32Ω receiver 16Ω receiver or 8Ω 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 22 and Figure 23 Figure 22 SPK Frequency Response Horizontal axis is frequency longitudinal axis is loudness and unit is dB Note Qu...

Page 27: ...arison the green one performs the best and the blue one is second and the red one is the worst 2 8 Component of Microphone 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 2kΩ If RF TDD noise is detected at the MIC please contact MIC vendor for product with better RF suppression capability Furthermore the microphone channel ...

Page 28: ...2 M80 has three audio channels in hardware named AIN1 AOUT1 AIN2 AOUT2 and AOUT3 Channel AOUT3 is used as output of hands free application Software channel 0 is applied as hardware channel AIN1 AOUT1 Software channel 1 is applied as hardware channel AIN1 AOUT1 3 1 AT Command Audio parameters will be introduced as following chapter and audio parameters can be set via AT command 3 1 1 AT QAUDCH AT Q...

Page 29: ...io channel default 1 Headset audio channel 2 Loudspeaker audio channel AT QMIC a Test Command AT QMIC Response QMIC list of supported channel s list of supported gain level s OK Read Command AT QMIC Response QMIC gainlevel Normal_Mic gainlevel Headset_Mic gai nlevel Loudspeaker_Mic OK Write Command AT QMIC channel gain level Response OK If error is related to ME functionality CME ERROR err Referen...

Page 30: ...in level is too high receiving distortion would happen gain level Range is 0 15 AT CLVL Test Command AT CLVL Response CLVL list of supported level s OK Read Command AT CLVL Response CLVL level OK Write Command AT CLVL level Response OK If error is related to ME functionality CME ERROR err Reference GSM 07 07 level Integer type value 0 100 with manufacturer specific range Smallest value represents ...

Page 31: ...usted in hands free application AT QSIDET Test Command AT QSIDET Response QSIDET list of supported gainlevel s OK Read Command AT QSIDET Response QSIDET NORMAL_AUDIO gainlevel OK QSIDET HEADSET_AUDIO gainlevel OK Write Command AT QSIDET gainlevel Response OK If error is related to ME functionality CME ERROR err Reference GSM 07 07 gainlevel Gain level of side tone Value range 0 255 Disable 0 Note ...

Page 32: ...ara1 para2 para3 setting Response If op is read QAPS result list OK If op is write OK If format is error response CME ERROR err op Operation 0 Get old value 1 Set new value para1 Type of parameters 0 Input FIR Coeffs 1 Output FIR Coeffs 2 FIR output Index 3 Speech Common Para 4 Speech Mode Para para2 Group mode of parameters When para1 0 1 4 para2 is a must Ranges from 0 2 corresponding to the aud...

Page 33: ...audio parameters of normal audio mode software channel 0 QAPS 4 0 96 253 16388 31 57351 31 400 0 80 4325 99 0 20488 0 0 8192 OK AT QAPS 0 4 1 Read audio parameters of headset audio mode software channel 1 QAPS 4 1 96 253 10756 31 57351 31 400 0 80 4325 99 0 16392 0 0 0 OK AT QAPS 0 4 2 Read audio parameters of loudspeaker audio mode software channel 2 QAPS 4 2 254 224 3208 31 57351 24607 400 132 8...

Page 34: ...sue caused by bad circuits or mechanical structure Some of parameters can be modified to fix echo issue Advices of audio parameters in different application are provided in the next section 3 1 3 1 Description of Par0 Par2 and Par12 Par0 AEC NLP control word Value range 0 256 Disable 0 The large value has a positive effect on ECHO issue Par2 AEC Echo suppressor control word Value range 32512 0 Dis...

Page 35: ...00 0 80 4325 99 0 8223 0 0 8192 AT QAPS 1 4 0 192 253 5256 31 57351 31 400 0 80 4325 99 0 8223 0 0 8192 AT QAPS 1 4 0 192 253 2218 31 57351 31 400 0 80 4325 99 0 8223 0 0 8192 AT QAPS 1 4 0 248 253 2218 31 57351 31 400 0 80 4325 99 0 8223 0 0 8192 DTMF AT QAPS 1 4 2 128 224 2218 31 57351 24607 400 132 80 4325 99 0 8223 0 0 0 AT QAPS 1 4 2 192 224 750 31 57351 24607 400 132 80 4325 99 0 2079 0 0 0 ...

Page 36: ...it unsealed mechanical structure high SPK loud voice or high sensitivity microphone ECHO issue has a negative effect on talking TDD noise TDD noise could be present at the far end of the near end while talking RF power aptitude generates a burst keeping 576us in every 4 615ms It could be coupling to audio circuit The envelope curve of the RF burst could be present due to filtering effect and make ...

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