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Would you be able to review the attached schematic? It's largely taken from the TPA6166A2 EVM. "SPKR" and "MIC" are expected to be line level, with a high-impedance single-ended load on MIC. ESD diodes added at the TRRS jack as the system is expected to be used in a poorly-controlled environment. SCL and SDA pull-ups to 1.8V are elsewhere in the schematic.
There's a low-pass filter on SPKR as there may be noise sources in the system >10kHz and this system is mainly to handle speech only. The audio source is mono.
For summing the microphone outputs of two or more of these devices, what do you recommend--10k series terminations on each, connected together at the input to an opamp?
Thanks!
Steve
Hi Steve,
Sorry for the delay on this schematic review much of the team is Out of the office at the moment. I can review the schematic/ discuss with the team about the best option on summing the mic outputs. I will give a thoughtful reply tomorrow
Regards,
Arthur
Hi Steve,
Sorry for the delay here, we will get you a response today.
Brian
Steve,
I took a look at this with another apps engineer and we don't see any major concerns with the schematic. Using 10k summing resistors should work fine for multiple devices, but note you might need to adjust the value of the capacitor C2 to make sure it does not affect the frequency response as you add more 10k summing resistors. Depending on the loading you may or may not need a buffer. Keep in mind a long cable will add capacitance and a buffer would be useful in that case.
Brian
Thanks for sending this. This and the summing are all on one PCB. I could put an LM358 on each mic output, before the 10k summing resistors, to get around the frequency shift from the summing. Put in some no-stuff zeros to let us play with it a bit.
Thanks!
Steve