Quadrature Mixers

I’s and Q’s and negative frequencies, oh my! Today we discuss mixers and frequency conversion, in particular, quadrature mixers and Tayloe detectors: what they are, how they work, why you might want one, and what do we use all this I and Q stuff for anyhow?

Additional references:

Description Reference
Introduction to RF mixers Basics of RF Mixers in Radio Receivers, Alan Wolke (W2AEW)
Mixer theory and switching mixer operation Downconversion Mixers, Gino Giusi, Ph.D
Introduction to IQ signals and phasor diagrams Basics of IQ Signals and IQ modulation & demodulation – a tutorial, Alan Wolke (W2AEW)
IQ signal processing fundamentals, Euler’s identities A Quadrature Signals Tutorial: Complex, But Not Complicated, Richard Lyons
IQ phase relationships at positive and negative frequencies IQ Modulation, Keysight Technologies
The Tayloe quadrature detector Ultra Low Noise, High Performance, Zero IF Quadrature Product Detector and Preamplifier, Dan Tayloe

2 thoughts on “Quadrature Mixers

  1. Is there a noticeable non-linearity in the quadrature conversion because there is some hysteresis in the turn-on and turn-off voltages? I know I had to deal with this once when using an opto-isolator where the difference was substantial. I’m not sure about the behaviour of the gates.

    • No, the multiplexer is quite linear, which is important as that is a very desirable trait for a mixer. There’s a very detailed analysis done of the Tayloe mixer in this thesis paper.

      (Note: Mixers are inherently non-linear devices, so by “linear” above, I mean that when the switch is closed the output matches the input very closely; obviously there are no perfect switches.)

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