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Application Note 

Speakerphone/car kit hands free 

design 

Summary of Contents for Speakerphone/car kit hands free design

Page 1: ...Application Note Speakerphone car kit hands free design...

Page 2: ...obile Communications reserves the right to make modifications additions and deletions to this manual due to typographical errors inaccurate information or improvements to programs and or equipment at...

Page 3: ...design LZT 123 7895 R1A 3 Contents 1 INTRODUCTION 4 2 APPLICATION OVERVIEW 5 3 HARDWARE SET UP 5 3 1 SPEAKER AND MICROPHONE 6 3 2 EXTERNAL AMPLIFICATION 6 3 3 GR47 AUDIO PARAMETERS 7 3 3 1 Configurati...

Page 4: ...g external echo cancelling electronics This method is suitable for simple car kit applications where placement of speaker and microphone can be defined and may be effective in some office speaker phon...

Page 5: ...not achieved an acceptable level consider implementing an external echo cancelling circuit as presented in Application Note LZT 123 5102 3 Hardware Set Up The diagram presented in Figure 3 shows the r...

Page 6: ...kHz Output impedance 680 ohms max 1Pa 1 kHz Directivity 8 dB min 90 degree cone angle Current consumption 500 uA max S N ratio 40 dB min 0 1 Pa A curve Table 2 Microphone Details 3 2 External Amplific...

Page 7: ...osen surroundings by modifying the audio levels of the microphone path and speaker path These modifications were made by changing the values written to parameters n 1 and n 2 Parameter 1 TxPGA was adj...

Page 8: ...at the start of each call but does not hinder conversation and may last for a few seconds If this level of acoustic feedback is unacceptable for the desired application please consider implementing a...

Page 9: ...ds free design LZT 123 7895 R1A 9 APPENDIX Figure 1 Speaker Driver 2 Watt Vsw Cb Fb Vin GND LM2676 ADJ 4k7 33uH 10nF 100uF 1000uF 1k5 12V in 5V 30BQ040 10nF 5V 10k 47k AFMS AGND Vcc PVcc PGND GND OUT...

Page 10: ...Speakerphone car kit hands free design LZT 123 7895 R1A 10 Figure 2 GR47 Audio Block Diagram N opcode as used in AT instruction AT E2EAMS...

Page 11: ...7 5dB 11 25dB 8 Analog 2 Volume Mute to 14dB Mute 14dB 10 5dB 7dB 3 5dB 0dB 3 5dB 7dB 10 5dB 14dB 9 MicPath OFF MUTE Diff MIC ATMS 10 SpkPath OFF MUTE Diff BEAR AFMS 11 TxPCM 13 or 16 bit 13 bit 16 bi...

Page 12: ...Speakerphone car kit hands free design LZT 123 7895 R1A 12 Figure 3 Locating Speaker and Microphone Inside Vehicle...

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