IMP23ABSU hardware interface

[NCatt.1]

Hello, 

I have as project to use the STWINKT1B board and write my custom code to read IMP23ABSU sensor at its maximum capacity (80kHz). I understand the sensor output data is amplified by an op-amp and can be read with ADC input of the microcontroller, but what is the exact interface ? I don't really understand the schematics logic of the sensor (Why is there 2 ouputs: "MREF" and "M1P_FILT", why are 2 op-amps used)

Could you please give me more details ?

Then, is there some basic examples of how to read the sensor ? ADC input configuration, sensor configuration, reading...

Thank you

[Federica Bossi · Accepted solution]

Hi @NCatt.1 ,

The circuit of that amplifier is used to centre the signal around Vdd/2, to exploit the full dynamics of the microphone up to the AOP (acoustical overload point). The MREF_DIV is in fact obtained by halving Vdd of the Mic with a divider, and through the buffer configuration the output MREF follows the input signal. The M1P_FILT signal, on the other hand, is precisely that of the microphone, which passes through an amplifier in a non-inverting configuration, with amplification factor 1 + R6/R7 = 2.34. This amplification factor is to take advantage of the microcontroller's 3.3V. The micro's ADC then acquires on IN1 the reference Vdd/2 and on IN2 the amplified signal centred around Vdd/2.

[vselvaraj]

Hi @Federica Bossi, 

I am working on integrating IMP23ABSU into my hardware. Hence, I reviewed the evaluation schematic (steval-stwinkt1b) to understand its setup. I have a few questions regarding the schematic, in addition to what has been answered above, it would be great if you could answer them.

1. There are a total of three MREF in the schematic for steval-stwinkt1b, part of which is attached to this message showing them. I understand what the ones circled in green correspond to based on your previous response. But what does the MREF, circled in red, correspond to?

2. In your response above you mentioned that the amplification factor of 1 + R6/R7 = 2.34 is to take advantage of the microcontroller's 3.3V. But isn't the Opamp's VCC+ and microcontroller's VREF+ tied to 2.7V? Meaning the analog voltage range will be from 0 to 2.7V and the output M1P can range from 0 to 2.7V, am I correct in interpreting the setup?

Thank you.

 

[Peter BENSCH]

@vselvaraj You've asked the same question here, please see my answer there, which also corrects some of @Federica Bossis statements.