bc127 analog input

IoT Modules WiFi and Bluetooth Modules
1

Hi!

We are working on cleaning up our audio interface from our codec to the BC127. The lineout of our codec is connected to MIC_LP of the BC127. (we don’t have the MIC_BIAS_A connected and MIC_NP is connected to ground) What is the expected input level of the mic? our codec outputs a signal that swings about -1.2V to +1.2V (2.4Vpp). would that be ok?

Somewhere I read that the recommended AUDIO_ANALOG (input_gain) should be 0, but in our case if that is set to 0 then the captured (recorded on iPhone Voice Memos) audio is quite low. Setting of 8 seems to be ok, and 15 seems to saturate.

I also just noticed in a datasheet a recommended schematic for microphone in that case the input would be offset by 2.6V and swing between 1.4 and 3.8V.

I guess the question is what is the expected range by the ADC of the BC127 to avoid saturation? What are the recommended gain settings? are there other settings that we should consider (digital gain)?

Thank you in advance for your help

2

Pretty late to respond to this, but the documentation on this is frustratingly vague so it may be helpful to other people. Basically I had to learn by trail and error. The method I used was to have (x2) BC127 discovery boards connected in analog audio with A2DP. I then sent a sinwave, blocked by a high capacitance capacitor (get rid of any DC bias interfering with the signal) and varied the voltage. I then monitored the output with an oscilloscope and kept incrementally increasing the input until I saw it was clipping. An example of what I found was that with AUDIO_ANALOG=10 10 1 OFF, the maximum input waveform was about 0.67V.