Hello All,
I need some assistance in reducing the mic input noise we’re hearing with the TLV320AIC3254 and TLV320AIC3204. It sounds like white noise. I’m using a single-ended mic configuration with 10K input resistors and a headset. It’s not a super high level of noise, but it is noticeable. Our gain is set to 35 dB.
To isolate the problem, I put the microphone in ADC bypass using mixer amplifiers mode (5.3.2 in datasheet). This routes the microphone level signals to the headphone output fully bypassing the ADC and DAC. I hear the white noise even if I remove the microphone, or ground out the mic input. Therefore, I don’t think it is the microphone generating the noise. I do get the least amount of noise by selecting the lowest mic bias voltage generated by the LDO.
The DAC performance is excellent. When I output a sine wave from the I2S interface it sounds great. When I output zero to the I2S DAC interface, the headphones are absolutely quiet. Therefore, I’ve narrowed the problem down to the analog input (PGA and mic bias).
So far we’ve used the AGC with the noise threshold (74 dB) to gate the noise. This sounds good if you speak into the mic at high enough volumes to overcome the noise threshold. Some quieter talkers have trouble with this, and if we lower the noise threshold anymore to accommodate them, the noise starts to cut in and out again.
We have all the unused inputs capacitively coupled and grounded.
Any ideas would be appreciated. I’ve been through all the register settings and cannot seem to find anything else to do programmatically. I’m not sure the 3254 DSP functions with pure path studio would help eliminate the noise either.
Thank you,
kurt