Hi
I have been experiencing unacceptable noise on the mic bias in the CC85XXDK EVM (see "CC85XXDK - Bi-Directional Audio Noise"; FW1.4 on Dec 11, 2012, and "300 Hz Noise related to transmission timeslots using CC8531 + CC2590" on Mar 6, 2013)
I received the following answer:
Yes, the microphone connector on the EB is a little noisy. Care has to be taken to avoid noise when making a final product:
- Differential is preferable compared to single-ended.
- Separate ground and power planes for RF and audio should be considered.
- Lengths for the traces carrying audio signals and clocks is of importance.
- Avoiding ground loops is key.
Have also used the on-board EVM 3.3V and 5.0V regulator outputs, which also produce the same unacceptable noise.
I have since tested the EVM with external mic bias and the noise is non-existent.
Do you have any solution to this on boards with high and periodic current demands in terms of filtering the AIC3101 mic bias or the mic input circuitry. My application is speech in noisy environments which will be filtered to exclude low frequency (up to say several hundred Hz) and high frequency (from say 5 KHz and up), so high fidelity is certainly not our aim.
Many thanks for answering the last post so quickly in reference to AIC3101 Filters.
Regards,
Geoff Pickford
