Author Topic: Opamp basics - electret mic peak detector  (Read 3056 times)

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Offline Zbig

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Opamp basics - electret mic peak detector
« on: November 05, 2013, 01:51:40 am »
Hi everyone

I was looking for a solution for an electret microphone amp/peak detector and came across this While I think the guy has made a great job at explaining this, I'm not sure I properly understand why he has intentionally introduced a DC offset on U1 by using virtual ground equal to Vcc/2 (
), an offset he has to cancel later on. Is it because the microphone signal could swing below ground or above Vcc (or could it? I'm not sure) otherwise? Or maybe it's there to bias the D3 diode above its Vf so the signal doesn't have to "shoot through" it, i.e. detector isn't effectively limited to V > 0.6V?

I'd appreciate any help in understanding this.
« Last Edit: November 05, 2013, 01:54:46 am by Zbig »
 

Online w2aew

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Re: Opamp basics - electret mic peak detector
« Reply #1 on: November 05, 2013, 02:30:08 am »
Hi everyone

I was looking for a solution for an electret microphone amp/peak detector and came across this While I think the guy has made a great job at explaining this, I'm not sure I properly understand why he has intentionally introduced a DC offset on U1 by using virtual ground equal to Vcc/2 (
), an offset he has to cancel later on. Is it because the microphone signal could swing below ground or above Vcc (or could it? I'm not sure) otherwise? Or maybe it's there to bias the D3 diode above its Vf so the signal doesn't have to "shoot through" it, i.e. detector isn't effectively limited to V > 0.6V?

I'd appreciate any help in understanding this.

It's mainly because many op amps, like the LM324 he showed) have an input common mode range that does NOT include the supply rails.  In other words, the voltage at the input must be between the supply rails. 

For more info on this, see my video on this topic:
YouTube channel: https://www.youtube.com/w2aew
FAE for Tektronix
Technical Coordinator for the ARRL Northern NJ Section
 

Offline Zbig

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Re: Opamp basics - electret mic peak detector
« Reply #2 on: November 05, 2013, 11:49:31 am »
That is a great tutorial, thank you! :-+
 

Online w2aew

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Re: Opamp basics - electret mic peak detector
« Reply #3 on: November 06, 2013, 02:38:40 am »
That is a great tutorial, thank you! :-+

Thanks.  Since the topic was on a peak detector, you might also enjoy this video that I put together:
YouTube channel: https://www.youtube.com/w2aew
FAE for Tektronix
Technical Coordinator for the ARRL Northern NJ Section
 

Offline Zbig

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Re: Opamp basics - electret mic peak detector
« Reply #4 on: November 06, 2013, 05:36:32 pm »
I certainly did, thanks!
 


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