Here is my take on XOR versus Inverter as a mixer.
The XOR, with two digital inputs (for example divided down from RF signals) will act as a phase detector. The output will be zero when two, 50% duty, digital inputs are exactly out of phase. Okay to be clear, an XNOR will be zero ¨C a XOR will have flat positive output.
As the two inputs deviated from that phase and/or frequency, it will generate pulses that can be averaged using and RC or integrator to give you an analog representation of the phase difference.
I had seen these in PLLs for example, since that uses a phase detector.
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To use an inverter as a mixer, I am guessing you would do the trick where you bias it up as a linear gain block (two large series resistors from OUTPUT to INPUT, with maybe a bypass cap to ground at the miid-point). This creates a very high gain (analog) amplifier, so when you combine two input signals and apply to the input, it will bang rail to rail, basically it¡¯s a nonlinear gain block, and you get that square law behavior that is the classical mixer: (SinA + SinB) ^2 which expands to the sums and differences (and some DC).
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I once measured a CD4049 inverter, biased as an amplifier, at 10.7MHz, and was amazed that it was >50dB, and I believe it consumed about 10mA.
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Dan
