I have a non-reciprocal 2nd order non-linear circuit as below, I want to study the intermodulation at the output
Ha, Hb are both the pi-section lowpass filter as below
Then I run 2-tone Harmonic Balance simulation, f1 = 700MHz, f2 = 900MHz.
Then I obtain the output spectrum
Now if you will, focus on the frequency 140MHz and 180MHz (which is 2*f1 and 2*f2)
HB result shows that the magnitude is around 0.5V. However, when I use the analytical expression to compute, the values are about twice as much. Other than that, HB agrees quite well with the analytical expression.
The picture below is the output voltage vs each combination m*f1 + n*f2. Pink circles and stems are from HB simulation, blue circles are from analytical expression. As illustrated above, whenever m and n are not 0, they agree well. Only when m or n = 0, HB result is always about half smaller than that from the analytical expression.
Could anyone please tell me if I'm doing something wrong with HB simulation?