mic preamp

[dragon91]

ok..... thanx for the help.... But I really need to clarify one thing... the mems mic I got from knowles acoustic is a mic with a preamp integrated with it.... which means the mic which is really small has an opamp integrated with it already..... The maximum gain that can be set for this opamp is 10..... u can check the data sheet for my opamp and its in built opamp schematic... Now that I am sure I need to dc bias and ac couple the first stage of my opamp.. I am wondering how if the first stage is already in-built in the mic without a dc bias or ac coupling.. or maybe it is set at a different dc bias and it has no ac coupling.... please can someone suggest a better way to implement a filter and amplify the signal with this mic...

Just needs an input coupling capacitor now, as the source is shorting the bias out.

 

[Nigel Goodwin]

The mike has biasing and coupling capacitors in it - you don't have a circuit diagram of it, so how would you know?.

The block diagram in that PDF isn't a circuit diagram, it's only showing a few of the components, just the ones you need to know about in order to use it.

So why are you trying to add it to your own circuit?.

 

[dragon91]

I actually need to use a mic as a sensor equipment for my project..... But for the mic to be a sensor it needs to be small and surface mountable... It seems the only mic that can do that is the knowles mems mic series....

 

[dragon91]

I would really appreciate it if u can tell me if there is a way to amplify and filter the signal from this mic...

 

[Nigel Goodwin]

I would really appreciate it if u can tell me if there is a way to amplify and filter the signal from this mic...

An active filter followed by an amplifier stage, or an amplifier followed by a filter stage - it's a dead simple task.

But you bizzarely keep adding extra non-functional stages at the front?.

 

[audioguru]

Your filter has a gain of 2 (not unity gain) and way too much feedback so it is an oscillator. Look at Sallen and Key filters in Google.

Your "gain of 10" opamp does not work because its input is missing a DC bias voltage. If it was biased then its output would be saturated against the positive supply rail because its feedback is missing a capacitor to ground. If it worked then its gain would be 11, not 10.

Here is a simple Butterworth lowpass filter:

 

[dragon91]

Is it possible to use a filter from 0 HZ to 130 HZ... would that cause any problems in my circuit????

 

[Hero999]

Yes, use a low pass filter with an upper cut-off of 130Hz.

 

[dragon91]

Can anyone tell me the name of a microphone which is sensitive enough to detect frequency's as low as 1 HZ........ Actually the mic I am using loses its sensitivity below a 100 HZ......

 

[audioguru]

You cannot hear frequencies below 20Hz. The response curve of a high quality electret mic stops at about 22Hz because they do not have anything to accurately produce lower frequencies.

1Hz is almost DC. It is air moving slowly back and forth.
Why do you want to detect 1Hz?

 

[dragon91]

******************************************

 

[audioguru]

The water jet will make air vibrate at a very low frequency only if it is very large. Look at the size of a woofer speaker then look at the size of a sub-woofer speaker. Look at the size of the vocal chords of whales.

 

[Hero999]

You also need to go down to 0Hz (DC) which isn't possible with a microphone, may be a barometer could be used for the really low frequencies?