Hello all

I have a linear frequency modulated (LFM) signal having 90 KHz center frequency and 20 KHz bandwidth around it. My problem is to demodulate it at base band to get I and Q both (phase information required). I have searched a lot at internet but mostly found quadrature demodulator ICs have starting input frequency range in MHz. AD8333 was what i found having lowest input frequency but even it does not work for 90 KHz (as i discussed with analog devices technical staff).

Can any one kindly guide me how to solve my problem?.

Thanks in advance

Best Regards
Nauman

 

You might try a pair of frequency to voltage converter chips....which are quite inexpensive these days. You'll still have to build the quadrature reference oscillator, which is very simple at such frequencies.
Eric

 

You might try a pair of frequency to voltage converter chips....which are quite inexpensive these days. You'll still have to build the quadrature reference oscillator, which is very simple at such frequencies.
Eric

Thanks for reply. Can you kindly elaborate more how to use frequency to voltage converters in quadrature demodulation circuit?

Thanks in advance
Nauman

 

As the frequency is swept on the input, the voltage output looks like a sawtooth, starting at a low value and rising linearly to some maximum value and returning to a low value. It should duplicate shape and timing of the control voltage on the VCO in the transmitter.

 

Read this.

http://www.wparc.us/presentations/SDR-2-19-2013/Tayloe_mixer_x3a.pdf

 

Read this.

http://www.wparc.us/presentations/SDR-2-19-2013/Tayloe_mixer_x3a.pdf

Thanks. I will read it and then bother you again