How can you see the output waveforms of the simulation results? the time duration in which the output of Flip flop is being constant, without any change, can be equal to the hold time. In master-slave flip flops, the hold time is approximately equal to the half of the period time. in edge-sensitive flip-flops, it rises to around period time of sampling clock.
If I can see the waveforms, how can I measure the hold time ?
I mean how should I proceed ?
If you are using cadence tools(virtuoso), once simulation is finished and waveforms are visible in VIVA browser, you can place 2 markers after zooming on the waveforms for clock period and signal. thereby you can read the values manually, from the waveforms.
OR
Just go to the VIVA calculator and create an expression for edge of signal.
First method is manual and required some precision to place markers at correct position. (usually 10% to 90% of the signal value).
In Spice engines that support mixed mode primitives, internal delays are set as parameters, say Trise=20n and that's about it. You may set maximum timestep during simulation, and even finer during transitions by TRIPDT parameter, but even then you are looking at the model where transitions speed is predetermined. Such behaviour will be close to the real world behaviour only if that flip flop was modelled correctly, and even then it will be idealised. So in essence you are only double checking if the models are doing what they are supposed to do.
In short, seek a command like ".tran 0 1 0 5u" and change the "5u" into "5n" as nanoseconds are the time frame you are looking for (in a traditional CD4000 series). It will make your simulation very slow and results very big, so you may add a line "TRIPDT=5e-9" in digital primitives declaration that will force finer timesteps only during transitions and let Spice decide on proper timesteps elsewhere.
You need to look at time difference between clock edge and a Q transition edge.
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