Harmonic balance to simulate Gilbert mixer?

[katrin]

Dear All,

I am using HB to simulate a standard Gilbert mixer, I add LO and RF frequency in the HB simulator, their order are 5.

What confuses me is the output spectrum shows not only RF+LO and RF-LO, but also the other higher order harmonic whose power are very high and could even be comparable to the basic harmonic output power.

For instance, the output power at 2*frequencyRF is always very high, but from theory, the Gilbert mixer should prevent feedthrough, even it is at 2 times the input RF frequency. so it is hard to believe this output spectrum.

Anyone has some idea about it. Thanks very much.

 

[unkarc]

Hi,

I suggest reconsider the RF and LO input levels to your mixer, the best would be to start from a very low level in both cases where the mixer cannot be overdriven yet. Reconsider also the load impedance which may transform back into your active mixer direct output (I mean the collectors or drains).
And then gradually increase the input to see how fast the unwanted spuree increases and that the RATE of increase is what can be expected from a 'linear' mixer.

Also, your simulator may be using active device models which are not so "accurate" to this task, this also a possibility for erratic simulation results.

rgds
unkarc