-1
\$\begingroup\$

For small frequencies (20-20000Hz) the opamp has output more than -3dB

If we make a low frequency AM receiver , can we use an opamp for demodulation instead of a diode and for amplifications instead of a transformer?

\$\endgroup\$
8
  • 2
    \$\begingroup\$ errrrr........ no \$\endgroup\$ – Andy aka Oct 10 '20 at 18:19
  • \$\begingroup\$ @Andyaka Why not? \$\endgroup\$ – ArtOfElectronics Oct 10 '20 at 18:21
  • 1
    \$\begingroup\$ So what is 20-20000 Hz? The signal being modulated, or the carrier used to modulate the signal? \$\endgroup\$ – Justme Oct 10 '20 at 19:31
  • \$\begingroup\$ @ArtOfElectronics: An AM receiver doesn't have to have a transformer. Look up simple crystal radios. An inductor, a capacitor, a diode, and a high impedance earphone. No transformer is needed. \$\endgroup\$ – JRE Oct 10 '20 at 20:07
  • 5
    \$\begingroup\$ @Art, as suggested already in comments to one of your previous questions, you need to study electronics and understand how various circuit combinations work, why they work and where they can be used. You do this by studying existing designs and figuring out why they were designed that way. Your approach of cobbling together random bits of circuits isn't going to be efficient in your use of time - or ours. \$\endgroup\$ – Transistor Oct 10 '20 at 21:07
1
\$\begingroup\$

The transformer gives gain without noise, but you can replace the diode with an LM1496 balanced Demod with 85dB carrier suppression.

An Op Amp demod is too noisy and poor carrier suppression at 1MHz due to lack of GBW.

  • GBW must be 300 MHz for transadmittance to get this performance.
\$\endgroup\$
2
  • 1
    \$\begingroup\$ I am targetting at frequencies 20-20kHz. \$\endgroup\$ – ArtOfElectronics Oct 10 '20 at 18:54
  • 1
    \$\begingroup\$ Yes but AM is >1MHz and But what is your IF, LO frequency? Radios. Do not direct convert RF, the demod must handle IF frequency to get20~20kHz out yet AM is limited to 7kHz ... go read learn \$\endgroup\$ – Tony Stewart EE75 Oct 10 '20 at 22:38
1
\$\begingroup\$

I think, looks like to me and forgive me if I am wrong, you confuse modulation signal (the information you want to obtain) and carrier that is the high frequency signal which its amplitude is modulated. Again, if I am not wrong, when you refer to the range 20~20000Hz you refer to audio signals that is the usual bandwith. The 20KHz can be managed by any opamp but the several MHz used for carriers not.

\$\endgroup\$
0
\$\begingroup\$

I found this circuit from wikiHow that is about a demodulator using opamp:

https://www.wikihow.com/Create-a-Simple-AM-Radio?amp=1

\$\endgroup\$
1
  • \$\begingroup\$ Tony Stewart is right on. I would suggest looking for a more modern OP-amp. \$\endgroup\$ – Gil May 27 at 14:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.