0
\$\begingroup\$

I have an FM signal: 200 mVpp, 11.5 MHz carrier, max deviation - 500 kHz, modulating signal frequency range is 40-10000 Hz. And I need to demodulate it with highest SNR possible.

The circuit has to be low voltage (3.3V or lower), low power and low profile (<4mm, so no large inductors or transformers). What are the best ways to demodulate the signal? I've found this circuit (autodyne frequency converter and pulse counter), it has very low power consumption, can be made in low profile and doesn't require much tuning, which is also great, but I'm not sure about it's noise performance. I also think about multiplying signal frequency 4-5 times with PT7C4511 clock multiplier and then demodulating it with TLC2933 PLL.

UPD: I've found an interesting patent which claims low noise demodulation. What do you think?

\$\endgroup\$
  • 1
    \$\begingroup\$ I raised a very similar question here but I didn't really get enough answers \$\endgroup\$ – Andy aka Apr 22 '18 at 8:00
  • \$\begingroup\$ Can you bandpass sample? Software radio basically. \$\endgroup\$ – Andrés Apr 22 '18 at 15:09
  • \$\begingroup\$ @Andrés isn't software radio too power consuming? Also my circuit must have analog output. Bandpass sampling makes no sense to me since it's basically a frequency downconversion (ADC works as mixer and sampling frequency as LO). \$\endgroup\$ – Archimedes Apr 22 '18 at 16:00
  • \$\begingroup\$ That depends what you want the signal for in the end. xyproblem.info \$\endgroup\$ – Andrés Apr 22 '18 at 21:45
1
\$\begingroup\$

The standard technique these days is to use a PLL. You could use an IC which does everything for you, or (at that relatively low carrier frequency) you could build your own VCO and use a 74HC series (good to 25MHz) XOR gate as your phase detector. Then you just need to AC-couple the VCO control signal to your audio amplifier.

\$\endgroup\$
  • \$\begingroup\$ Are there any ICs that do everything for me besides 4046? (it's VCO has terrible phase noise) \$\endgroup\$ – Archimedes Apr 22 '18 at 15:13
  • 1
    \$\begingroup\$ I've been looking at the LMX2332A for a VHF/UHF application, but it doesn't quite go as low as 10MHz. It's designed to produce the mixer frequency and do the IF FM demodulation (or produce an IF mixer frequency for SSB demodulation) in one chip, so if you've already got a superhet stage you could replace part of it with that. There should be similar ICs which can work directly in the HF band. \$\endgroup\$ – Chromatix Apr 22 '18 at 21:23
  • \$\begingroup\$ Will not the NE604 provide this behavior? \$\endgroup\$ – analogsystemsrf Apr 24 '18 at 6:00
  • \$\begingroup\$ No, that isn't a PLL chip at all; you have to provide an external oscillator at IF freq, and it includes a quadrature detector instead. It might solve the OP's question, so maybe post it as its own answer. \$\endgroup\$ – Chromatix Apr 24 '18 at 7:57

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.