So my question is this: How to convert sampled real audio signal to it's IQ components for IQ modulation?

For instance: WHen I have my DSP or FPGA receive a audio signal through a ADC, which is just the RAW A/D value. Now I want to run this through a DAC to IQ modulator to get let FM modulation.
How would I convert the raw A/D value into IQ? How do i break this signal down to In-phase and quadrature component? Do I do FM modulation in the DSP/FPGA and get the IQ from that or just split the audio baseband into it's IQ components?


I'm in the process of converting FSK transmitter from older obsolete design to newer design. So as I'm studying IQ, i was wondering what would happen if I wanted to send a analog sine wave through the IQ modulator, like LTC5599. How would I convert a analog sine wave to I and Q send it as input to the LTC5599?

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    $\begingroup$ Can you explain what you're trying to do in a little more detail? I'm having trouble understanding what the problem is. $\endgroup$
    – MBaz
    Sep 20, 2018 at 20:54
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    $\begingroup$ Do you want to modulate or demodulate? You could assign even bits to your I signal and odd bits to your Q signal if using modulation (QPSK). Then you could FM modulate the QPSK signal. If you are demodulating an IQ signal then you would need to detect the phase so you can apply matched filters to the I & Q legs correctly. $\endgroup$ Sep 20, 2018 at 22:36

1 Answer 1


I’ll answer the question I think you’re asking here:

If you have a real valued signal that came right out of an A/D and you’d like to recover signal phase, you can use the Hilbert transform to generate a version of the signal that is in quadrature with your A/D output. In this case, your original real valued signal would be the I component (in-phase) and the output of the Hilbert transform multiplied by j, the imaginary number, would be your Q component (quadrature).

Now if you have some modulation you want to deal with, you would do the IQ recovery first like I just described; once you have that IQ signal you’re pretty much completely characterized the signal, so you can do just about whatever you’d like with it while preserving phase.

  • $\begingroup$ If I have a real analog signal, i.e audio from a microphone or speaker out,and did hilbert transform on it, i will get the I and Q components I needed? $\endgroup$ Sep 21, 2018 at 13:02
  • $\begingroup$ Yes, that is what the second paragraph says; the real input would be the I component and the output of the Hilbert transform would be the Q component. $\endgroup$ Sep 21, 2018 at 13:23
  • $\begingroup$ Awesome! Thank you for clarifying this for me. $\endgroup$ Sep 21, 2018 at 14:03

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