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In electric-circuit theory due to superposition for an LTI system, the voltage can be thought such that it is sum of of a transient response plus a steady state response.

For example below the voltage waveform's steady state response is a sine and the transient response is an increase with negative exponential.

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The above is an example. Is it possible to view only the transient response of such waveform in LTspice by not using a complicated circuitry? What came to my mind something like a peak detector but I don't know how I can accurately implement it by a behavioral source ect.

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In order to subtract the steady-state response from the transient waveform, you will always need prior knowledge about the steady-state itself. The simulator has no way of looking in the future for transient simulations.

The easiest way is probably determining the output amplitude and phase (because the system is LTI) and then subtracting it from the output. This amplitude and phase can be found by executing an AC analysis.

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I don't know if I understand good your question (would appreciate more details), but in LTSpice there is an option for stopping the simulation once the steady state is reached. Depending on the circuit that you have might be useful.

And as the answer by Sven B says, an option too is to remove this steady state solution afterwards: with another source on the circuit or directly with some math on the graphics. You can also calculate the average values in a certain period (where you know is already steady state) for that with some commands (examples below). Possibly the AC simulation can help you as well for characterizing the steady state and removing it on the transient simulation.

Although I still don't get why would you want to do it? you wanna see only the ripple? the peaks?

--Examples of calcs within a time periode:

.param t=0 .step param t 0 100u 10u .param S=10u .meas tran IinRMS avg( I(R1)**2 ) TRIG time VAL=t-S/2 TARG time VAL=t+S/2

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