Integrating SARA-U270 together with NAU8814 audio codec

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screep
Posts: 1
Joined: 23 May 2019, 19:50

23 May 2019, 20:05

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+USPM=255,255,0,0,2",
"AT+UI2S=1,1,1,3,0",
"AT+USPM=1,1,0,0,2",
"AT+UMCLK=3,1",
"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:

"AT+UPAR=2,0,0"

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
Attachments
bypspk.PNG
TEST point
bypspk.PNG (232.56 KiB) Viewed 2939 times

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