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 |
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.)