Rise/Fall time calculation

Dear mxm14,

mxm14 said:

Since i want to calculate the rise/fall for several corners,i want to substitute those numbers with a formula....  Which is the formula used to extract the average amplitude from the amplitude with ripple?

One possibility that will provide a reasonable estimate for the average logic low and logic high amplitudes (for most waveforms - but not all cases!) is to utilize apply a moving average function to the periodic waveform of interest. In a few tests I conducted, if I use about 10% of the points per period of the waveform, the maximum and minimum values of the moving average appear to be reasonable estimates of the average logic low and logic high amplitudes. Figure 1 details a couple of cases showing the waveform (orange) and moving average trace (dotted blue). Mr. Andrew Beckett has written a moving average function in SKILL that can be used in both the Calculator as weill as in an Assembler or Explorer output expression. The latest version I have of his function, "abMovingAvg.il" is dated Jan 13, 2020. it is available from the Cadence on-line support site. Hence, I might suggest your define the two outputs average_logic_low and average_logic_high where each is defined as follows for your output waveform "/vout".

average_logic_low = ymin(abMovingAvg(v("/vout" ?result 'tran)  <time_interval_corresponding_to_10%_of points_per_waveform_period>))

average_logic_high = ymax(abMovingAvg(v("/vout" ?result 'tran)  <time_interval_corresponding_to_10%_of points_per_waveform_period>))

Use these two variables, average_logic_low and average_logic_high in your riseTime() expression. This will make the average logic high and low values a function of the simulation corner.

I hope this helps mxm14!

Shawn

Figure 1

The functions you are looking for are the baseLine() and topLine() functions which return the statistical peaks of the signal. These are documented, but aren't in the calculator (yet). I filed a change request (CCR 2855771) for two things - one to ensure they handle family waveforms, and two to add them to the calculator/expression builder. For now you'll need to type (say) topLine(VT("/out"))

Andrew

The functions you are looking for are the baseLine() and topLine() functions which return the statistical peaks of the signal. These are documented, but aren't in the calculator (yet). I filed a change request (CCR 2855771) for two things - one to ensure they handle family waveforms, and two to add them to the calculator/expression builder. For now you'll need to type (say) topLine(VT("/out"))

Andrew

Thank you Shawn and Andrew!