1. General Non-linearityx
f( )
y = f(x)
Any f(x) can be represented as a Taylor series expansion:
a0 represents a DC offset
a1 represents the linear gain
a2 represents the 2nd order response
a3 represents the 3rd order response
etc
We model devices as linear, but no practical devices are perfectly linear, so the Taylor coefficients are small, but not zero.
We are going to examine the second order response when the input, x, is the sum of two sinusoids having different amplitudes and different frequencies:

2. Let w2 = wRF wX = w2 – w1 w1 = wLO = wRF – wIF
The amplitude of the difference term is proportional to the product of the amplitudes of the generating signals.
Let w2 = wRF
w1 = wLO = wRF – wIF
(Low side injection)
wX = w2 – w1
Difference Frequency
Then wX = wRF – wLO = wIF
A 1 dB increase in the amplitude of either generating signal creates a 1 dB increase in the second order difference term.
wIF
wIF
wLO
wRF

3. Mixer Circuits

9. It’s a Radio!
A crappy one, to be sure, but …