8 Replies Latest reply on Dec 16, 2011 4:41 AM by userc_41579

# How to sample a microphone with best signal to noise ratio?

Hi,

I am trying to preamplify and sample a microphone signal, but I get a lot of noise.

The microphone gives a maximum of about 3mV of signal amplitude. So at the moment I use a single inverting PGA with gain 49 and try to use lowest possible range +/- 256mV of the 16-bit Sigma Delta ADC omitting it's input buffer. The signal to noise ratio of this setup seems to be only about 6 bits.

What is the best method using the internal amplifiers?

Many thanks!

Christof

• ###### 1. Re: How to sample a microphone with best signal to noise ratio?

cebersp,

Can you please let us know how you were able to arrive at the figure of 6-bits for signal to noise ratio?

Are you using a condenser mic for the project?

Regards,

dasg

• ###### 2. Re: How to sample a microphone with best signal to noise ratio?

I'm also interested in connecting a microphone to a PSoC5. Is there a cookbook recipe for this task?

• ###### 3. Re: How to sample a microphone with best signal to noise ratio?

You should try to send the output of your PGA to a pin and see if the noise is from the PGA or your input. I would prefer to use the op-amp if lower noise is needed.

• ###### 4. Re: How to sample a microphone with best signal to noise ratio?

The best gains are provided in the ADC itself. There is the buffer that can also provide you the gain.

With buffer gain set to 8 and ADC range set to provide a gain of 16 you can achieve an effective gain of 128.

• ###### 5. Re: How to sample a microphone with best signal to noise ratio?

Hi,

what bias are you using before the PGA? What DC bias does the mic output have?

Thanks.

• ###### 6. Re: How to sample a microphone with best signal to noise ratio?

Here is the microphone circuit

Design the values of R_1,R_2 and C_1 based on mic specifications and Vdd value. You may try connecting another capacitor across R_2 to reduce noise or to fine tune the response.

• ###### 7. Re: How to sample a microphone with best signal to noise ratio?

Since the ADC is best utilized in its digital config maybe making that resistor network with 3 resistors and gettting a differential input might help. Just a thought.

• ###### 8. Re: How to sample a microphone with best signal to noise ratio?

Since the ADC is best utilized in its differential config maybe making that resistor network with 3 resistors and gettting a differential input might help. Just a thought.