I am trying to connect a differential mems microphone’s positive output to a microcontroller.
The positive output of the mic has a nominal voltage of 0.8V. This means that if there is no sound the output is at 0.8V.
I want to make a diode + opamp circuit to get rid of this 0.8 V bias. I am only in interested in measuring the mic’s output above 0.8V.
If it's a differential microphone, why not connect it to the OPA as a differential signal? You can then use the OPA to set an arbitrary standby output voltage (e.g. half your ADC's range). This would also get rid of any common mode noise. Plus, it's much less thermally sensitive than a diode. And as you can set the gain, you can neatly put the signal to utilise most of your ADC range.
For that I will need negative rail. Also I am interested loud sounds at high resolution, so I want to use the ADC only for voltages about 0.8V. For noise removal the pcb is designed to be noise free and the manufacturing is done to keep every thing clean.
Can't you just divide the existing supply rail? Plenty of low voltage In. Amps around
We thought about that, but the final winner is a diode. Slight disadvantage in that it doesn't completely remove offset and has sensitivity to temperature, but the simplicity of it is good. Also diodes never run out of supply.
If you plan to interface the microphone's output to an A/D input of the µC, why not get rid of the offset voltage in software?
And, if the output signal of the microphone will be used as a digital signal, why worry about it being 0.0 V or 0.8 V? Probably, for the µC you're using, they are both logic level low.
Thanks. Yes offset removal in software is a definite contendor.
MEMS microphones comes with ASIC serial output and accepts clock input. Connect these lines with SPI interface of the microcontroller. It is simple.
Its an analog mems mic.