Unexpected DC offset captured in AIC3104 Mic1

Yulin

Other Parts Discussed in Thread: TLV320AIC3104

20151116_AIC3104.pdf

Hi TI experts,

A recording in a silent office shows a DC offset of +0.36 (full scale is -1 to +1).

Schematics is attached.
With below AIC3104 configuration
0~ 15 00 00 00 10 04 00 00 0A 00 00 00 81 00 00 40 7F
16~ 31 80 FF FF 04 78 78 78 78 78 46 00 FE 00 00 FE 00
32~ 47 00 00 00 00 C0 80 00 00 00 50 00 00 00 00 00 00
48~ 63 00 00 00 04 00 00 00 00 00 00 04 00 00 00 00 00
64~ 79 00 04 00 00 00 00 00 00 04 00 00 00 00 00 00 00
80~ 95 00 00 80 00 00 00 0B 00 00 00 00 00 00 00 90 00
96~111 00 00 00 00 00 01 02 00 00 00 00 00 00 00 00 00
112~127 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
I did the following record tests for more clues about this issue:
1. Remove R968 and R963, short MIC1LP and MIC1LM. --> output is +1.
2. Remove R968 and R963, short MIC1LP and MIC1LM to ground. --> output is -0.3175+/-0.0005
3. Remove R968 and R963, short MIC1LP and MIC1LM to MICBIAS of AIC3104. --> output is +1.

Please kindly help to identify the reasons.
Thanks,
Yulin.

over 8 years ago

0 Luis Fernando Rodriguez S. over 8 years ago

TI__Guru* 84915 points

Hi, Yulin,

It is suggested to add a 0.1uF dc-block capacitor at the analog inputs. Could you try using this capacitors instead the 10k resistors (R968 and R963)?

Please let me know if the problem persists.

Best regards,
Luis Fernando Rodríguez S.

0 Yulin over 8 years ago in reply to Luis Fernando Rodriguez S.

Expert 1625 points

Hi Luis,

As R968 and R963 are removed and MIC1LP is configured single-ended,
what voltage input to MIC1LP could make ADC to output value zero (or close to zero) ?

Thanks,
Yulin.

0 Luis Fernando Rodriguez S. over 8 years ago in reply to Yulin

TI__Guru* 84915 points

Hi, Yulin,

Please take a look at the following picture for details.

Best regards,
Luis Fernando Rodríguez S.

0 Yulin over 8 years ago in reply to Luis Fernando Rodriguez S.

Expert 1625 points

Hi Luis,

With R968 and R963 are removed, it is observed that MIC1LP goes to ~1.4v when recording starts.
Could you please indicate what it is for ?
And is it expected ?

Thanks,
Yulin.

0 Luis Fernando Rodriguez S. over 8 years ago in reply to Yulin

TI__Guru* 84915 points

Hi, Yulin,

This is an expected value. The TLV320AIC3104 has a common-mode voltage of 1.35V.

Best regards,
Luis Fernando Rodríguez S.

0 Yulin over 8 years ago in reply to Luis Fernando Rodriguez S.

Expert 1625 points

Hi Luis,

I am confused.
According to the ADC I/O characteristic curve you provided,
the voltage that leads ADC to output 0 should be AVDD/2 (~1.65v).
Why does MIC1LP (in single-end mode) output 1.35v rather than AVDD/2 ?

BTW, I did one more test:
4. Remove R968, connect a capacitor between MIC1LP ground, single-end mode with +60dB PGA gain.
--> output is 0.105V+/-0.025V and input to MIC1LP should be ~ 0.105mV+/-0.025mV
Do you think this is the right way to find the reasons that lead to the DC offset ?
Is "0.105mV+/-0.025mV" qualified ?
Could you please indicate directions to reduce this DC offset and noise ?

Thanks,
Yulin.

Audio

Audio forum

Unexpected DC offset captured in AIC3104 Mic1