Time vs. Freq. domain on non-linear diode limiter


Here is an example circuit...


V1's frequency is set to 10 MHz.

If I sweep the source voltage from 0.01 to 10 V in 1 step per decade (.01, .1, 1 and 10 volts) and run a voltage vs. time domain graph on V1 and R3, I see the expected limiting when V1's voltage rises above the diodes' voltage threshold. Great.

When I attempt to do the same thing as a frequency domain sweep, I see no reduction in amplitude for the higher voltages as I do see in the time domain.

It's been a while since I messed with SPICE, so may have forgotten something. However, I would expect to see some notional lowering of the output amplitude (with distortion of course) as the voltage rises over the diode threshold.

Anyone have thoughts on this observation?


by jshuggins
June 03, 2021

Hi @jshuggins,

This is expected. As per the CircuitLab documentation on Frequency Domain Simulation: "A linearized, small-signal model of your circuit is generated from the DC operating point. Depending on your circuit, this model may only be accurate for very small signals, so frequency-domain analysis is usually complemented by time-domain analysis to reveal nonlinear effects."

The frequency domain solver linearizes your circuit so nonlinear distortion / clipping won't be seen.

Depending on what you're trying to show, it's possible that a DC Sweep may show what you're looking for:

by mrobbins
June 03, 2021


by jshuggins
June 03, 2021

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