I've been measuring a Pin / Lim limiter with about 20dBm going into it and an open / short circuit on a sliding load on the output. Under certain phases the limiter is generating non harmonic related spurious. My signal is C band and the spurious is around 700 to 900MHz depending on the phase.
Can anyone explain the mechanism that is causing this.
It's a parametric oscillation. Your RF signal modulates the diode capacitance, generating a negative resistance, which allows oscillation determined by some other resonance in your circuitry, probably your sliding load. I have also seen them in limiters, sometimes generating a wide-band noise burst as the limiter turns on, then it settles down. Anyway, used to be a common method of amplification prior to GaAs FET.
Following on from Walshrj99's question. I am attempting to model the phenomina using a generic ADS PIN diode model with little success. Would the generic non-linear ADS pin diode model be expected to produce this effect?
I have simulated over a wide input power range with a load pull circuit on the output.
6 months 3 days ago - 6 months 3 days ago#650by madengr
Probably depends on the diode model, but all the models I'm looking at in MWO do not have a non-linear capacitance. That capacitance is not supposed to vary anyway in a PIN diode since the charges move too slow.
Maybe instead try a non-linear capacitor. Then using a DC+ 2-tone HB simulation, use the first tone as a drive signal, then the second as a probe signal, using it look at input impedance. It would have a negative resistance to cause the oscillation. The DC is needed since the phenomenon may not work if the swing goes below 0V and the capacitance curve has odd symmetry.
This is all just a guess on my part; may try it today if I find time.