TLV320ADC3140: The peak (noise) occurs at 8KHz, 16KHz

Motofumi Kibata

Part Number: TLV320ADC3140

We have connected a condenser microphone (ECM) to the TLV320ADC3140 and have been using the TLV320ADC3140's built-in MICBIAS to bias the ECM (see circuit diagram below).

When MICBIAS is "AVDD" (+3.3V),
　The peak (noise) occurs at 8KHz, 16KHz, ... KHz. (see measurement results below).

When MICBIAS is "Vref x 1.096" (+3.0V),
　The peak (noise) disappears (improves?). (see measurement results below).

Is it correct to think that this peak is generated when MICBIAS is set to "AVDD" (+3.3V)?

Also, in the case of "Vref x 1.096" (+3.0V), is it correct to assume that the TLV320ADC3140 built-in regulator will improve the peak?

We are using a sampling rate of 192kHz.

over 1 year ago

0 Daveon Douglas over 1 year ago

TI__Mastermind 26210 points

Hi Kibita,

The DC level or common-mode of the input signal is biased internally by the ADC and is dependent on VREF and AVDD. This is explained well in this application note:

Working With Analog Inputs in the TLV320ADCX120 and PCMX120-Q1 Family

For troubleshooting noise issue, please probe the signal following the capacitors at the input to ensure it is clean. If not, here are my comments:

I think your input signal may have induced noise due to the ECM microphone connection. The current connection would warrant the input to be single-ended, since the minus pin of the microphone is not referenced with half the impedance to GND.
- You can AC-coupling IN1m to GND if that is easier
- Typically an ECM mic connection is half the impedance of the mic pulled up to MICBIAS and half the impedance shorted to GND.
If your coupling capacitor is greater than 1uF, then you need to increase the charge time of the capacitor for proper operation. The default is for 1uF cap.

Regards,

0 Motofumi Kibata over 1 year ago in reply to Daveon Douglas

Prodigy 60 points

Dear Douglas,

Thank you for your comment.

I have an additional question.

I am seeing peaks at 8k and 16k, does the ADC (TLV320ADC3140) have a noise source that generates these peaks?

Best Regards,

+1 Daveon Douglas over 1 year ago in reply to Motofumi Kibata

TI__Mastermind 26210 points

Hi Kibata,

No, the peaks should not exist. But due to the fact that they are multiples of each other suggest that the peaks may be harmonics of some issue within the signal.

Regards,

0 Motofumi Kibata over 1 year ago in reply to Daveon Douglas

Prodigy 60 points

Dear Douglas,

Understood. Thank you very much.

Best Regards,

The TI E2E™ design support forums will undergo maintenance from July 11 to July 13. If you need design support during this time, open a new support request with our customer support center.

Audio

Audio forum

TLV320ADC3140: The peak (noise) occurs at 8KHz, 16KHz