Re: How can I subtract one frequency from another??

Frank wrote:

Hi all,
A pretty basic question, but I seem to be having a brain block about what
approach to take for this application.

I would like to take 2 different frequencies, between lets say DC to 1000Hz,
and subtract them from one another to get the output signal frequency as the
difference between the 2 signals.

For example, 400Hz in one input, 410Hz in the 2nd input, the output will be
10Hz.

My first instinct was to use an op amp as a comparator, then I thought of a
differential amplifier, then, I stumbled across some mixer schematics, and
PLL schematics, and then some really complex filter IC's, by that time I was
well confused.

I just want this to be as simple as possible, one IC if at all possible and
some periferal passives.

Could one use an LM324 configured as a differential amp? What confuses me is
the CMMR part of it, and the fact that the differential amp seems to only
"differentiate" voltage differences, and not "frequency" differences,
however the common mode rejection will reject like frequencies from both
inputs.
I'm pretty rusty on my op amps, so I was hoping someone might be able to at
least point me in the right direction with this.

Thanks!

;)


Use a count-up / count down counter IC; the difference is seen at the output.
.

Relevant Pages

  • Re: How can I subtract one frequency from another ???
    ... and subtract them from one another to get the output signal frequency as the difference between the 2 signals. ... differential amplifier, then, I stumbled across some mixer schematics, and ... Could one use an LM324 configured as a differential amp? ... What confuses me is ...
    (sci.electronics.basics)
  • How can I subtract one frequency from another??
    ... I would like to take 2 different frequencies, between lets say DC to 1000Hz, ... differential amplifier, then, I stumbled across some mixer schematics, and ... Could one use an LM324 configured as a differential amp? ... What confuses me is ...
    (sci.electronics.design)
  • How can I subtract one frequency from another ???
    ... I would like to take 2 different frequencies, between lets say DC to 1000Hz, ... differential amplifier, then, I stumbled across some mixer schematics, and ... Could one use an LM324 configured as a differential amp? ... What confuses me is ...
    (sci.electronics.basics)