QPSS with non-50% dutycycle square wave clocks (For sample and hold)

Hello,

Would anyone know how to setup a PSS or QPSS simulation with 25% dutycycle clock sources or if such a thing is possible with QPSS.

Fig1 (below) is a snapshot of the circuit I am trying to characterize. This has 4 clock ports each with 25%duty cycle in the ON state. Fig2 below shows two of these clocks.

Each path in the circuit consists of two switches with a low pass RC sandwiched in between. The Input is a 50Ohm port sine wave and the output is a 1K resistor. The output nets of all paths are connected together.

I am trying to determine the swept frequency response from input to output (voltage) when the input is from 500Mhz to  510MHz. The Period (T=1/Fp) of each of the pulses is such that Fp=500MHz. The first pulse source has a delay=0, second has delay=T/4, third delay=2T/4, etc...

I am currently getting it working and seeing the correct result (bandpass response) with Transient but the problem is doing a dft at 500MHz with 10KHz spacings needs at least 100us and takes up a lot of time and disk space.

Many Thanks,
Chris.

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Fig1

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Fig2

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