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Integrating SARA-U270 together with NAU8814 audio codec

Posted: 23 May 2019, 20:05
by screep
Hi, everybody!

I have troubles with microphone audio quality with NAU8814 audio codes integrated with UBLOX SARA-U270 3G modem.
Simple said, talking to microphone gets very poor sound quality. Probably in is not PCB trace problem, because I can
get very good sound quality on speaker activating audio BYPASS with BYPSPK bit in 0x32 register:

Sound looks like ADC overloaded... But I can't set proper amplification to achieve good sound quality.

There are following settings for SARA U270:

"AT+UI2CO=1,0,0,0x1A,0", // 1A=0x34

But I can't activate audio loop inside modem to check sound quality after passing all digital circuits:


NAU8814 register settings:

AUXEN disabled, MCLK - 26Mhz, IMCLK 12288000 Hz = (256*48000)

Register settings:

"AT+UI2CW=\"4A23\",2", // 0x25, 0 - PLLK
"AT+UI2CW=\"4DEA\",2", // 0x26, 1 PLLK
"AT+UI2CW=\"4F26\",2", // 0x27, 1 PLLK
"AT+UI2CW=\"0DA0\",2", // 0x06, 1 MCLK_SEL
"AT+UI2CW=\"4817\",2", // 0x24 PLLMCLK, PLLN
"AT+UI2CW=\"04FF\",2", // 0x02 BSTEN, PGAEN, ADCEN power management 2
"AT+UI2CW=\"023F\",2", // 0x01 power management 1
"AT+UI2CW=\"06FF\",2", // 0x03 speaker enable

"AT+UI2CW=\"0E06\",2", // 0x07, 0 - Audio sample rate control register - sample rate 48khz
"AT+UI2CW=\"5A3F\",2", // 0x2D PGA gain // 00 - 3F - currently set to maximum

"AT+UI2CW=\"5F00\",2", // 0x2F, 1 ADC boost - выключен
"AT+UI2CW=\"6202\",2", // 0x31 output register - thermal shutdown enabled

"AT+UI2CW=\"0810\",2", // 0x04 Audio inteface control
"AT+UI2CW=\"6C30\",2", // 0x36 speaker gain control // 0x37 - max
"AT+UI2CW=\"16FF\",2", // 0x0B // volume
"AT+UI2CW=\"460F\",2", // 0x23 // noice gain control register
"AT+UI2CW=\"5803\",2", // 0x2C // input signal control register - micbias 0.9 or 0.85VDDA - default value

Could you please give me any suggestions how to solve this problem.

Thank you in advance

Looking forward for your reply