Electronic – 90 Degree Phase shift at few MHz

phase shift

I have a seemingly simple question but I've been doing a lot of searching and can't find an answer.

What is a simple or standard way to achieve a 90 degree phase shift of an RF signal in the frequency range of ~1 MHz up to a few 10s or 100s of MHz? In the minicircuits catalog I see Hybrid couplers as low as 25 MHz so I would say 25 MHz and up is covered (though I don't know the cost) so the question can be narrowed down to how to achieve a 90 degree phase shift for a signal below 25 MHz?

In particular, in my specific application I have a signal which can be fixed in the range of 1-3 MHz that I would like to shift by 90 degrees. The 90 degree shifter doesn't need to necessarily need to work over a very large frequency range.

Ideas that I think would work but I don't know how well:

  • putting in a time delay with a length of cable. This is a bit inconvenient because it's a long length of cable (~10 m or more) and I don't have incremental control over the phase shift.
  • Put the signal through the stop band of a filter. This will give it a 90 degree phase shift but unfortunately it will also necessarily suppress the signal amplitude by a lot.. I've only thought about the case for a simple single pole filter
  • Digitizing the signal, somehow implement the phase delay digitally, then re-synthesize an analog output.

It seems like this should be something not too difficult, but in terms of commercial solutions I have only found products for higher frequency ranges. I can't tell if I can't find what I'm looking for because it's something so simple it's just not sold or if I'm searching for the wrong things or if there is some genuine difficulty with what I need. Any tips are appreciated!

I am asking for potential use in a modulation transfer spectroscopy system in which I need to generate a phase modulated (at ~3 MHz) signal at 80 MHz and then subsequently demodulate to extract the phase quadrature of a new signal generated at the modulation frequency. Both the phase modulation and phase quadrature detection could be done with the assistance of a 90 degree phase shifter and mixers.

edit: Clarification. I do NOT need a wideband phase shifter. I am curious about a general technique which could be used to phase shift a narrow band signal whose carrier may be anywhere in the range from 1-100 MHz. That is, say I have a narrowband 3 MHz signal. How can I give this a 90 degree phase shift? Say I have a narrowband 80 MHz signal. How can I give this a 90 degree phase shift? I do not need a wideband phase shifter. Apologies for the confusion. If different techniques are suitable for different frequencies within the range I have indicated then that is ok. I am at present most interested in a way to give a 90 degree phase shift to a signal which is like 3 MHz.

Best Answer

If you are happy with feeding a signal into a "block" and getting two signals out that are 90 degrees apart may I recommend this: -

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Select R = R1 = R2 = \$\sqrt{\frac{L}{C}}\$. This ensures that OUT1 and OUT2 have a phase differential of 90 degrees across all frequencies. The phase relationship between OUT1 and OUT2 is always 90 degrees but amplitudes do change with frequency as with any high-pass or low-pass fliter.