Issue link: https://resources.pcb.cadence.com/i/1180526
PSpice User Guide Analog behavioral modeling October 2019 369 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. initially set below the theoretical limit to (.25/TSTOP) and is then made as large as possible without inducing sampling errors. The maximum frequency has an initial upper bound of (1/(RELTOL*TMAX)), where TMAX is the transient analysis Step Ceiling value, and RELTOL is the relative accuracy of all calculated voltages and currents. If a Step Ceiling value is not specified, PSpice uses the Transient Analysis Print Step, TSTEP, instead. Note: TSTOP, TMAX, and TSTEP values are configured using Transient on the Setup menu. The RELTOL property is set using Options on the Setup menu. PSpice then attempts to reduce the maximum frequency by searching for the frequency at which the response has fallen to RELTOL times the maximum response. For instance, for the transform: 1/(1+s) the maximum response, 1.0, is at s = j·ω = 0 (DC). The cutoff frequency used when RELTOL=.001, is approximately 1000/(2π) = 159 Hz. At 159 Hz, the response is down to .001 (down by 60 db). Since some transforms do not have such a limit, there is also a limit of 10/RELTOL times the frequency resolution, or 10/(RELTOL·TSTOP). For example, consider the transform: e -0.001·s This is an ideal delay of 1 millisecond and has no frequency cutoff. If TSTOP = 10 milliseconds and RELTOL=.001, then PSpice imposes a frequency cutoff of 10 MHz. Since the time resolution is the inverse of the maximum frequency, this is equivalent to saying that the delay cannot resolve changes in the input at a rate faster than .1 microseconds. In general, the time resolution will be limited to RELTOL·TSTOP/10. A final computational consideration for Laplace parts is that the impulse response is determined by means of an FFT on the Laplace expression. The FFT is limited to 8192 points to keep it tractable, and this places an additional limit on the maximum frequency, which may not be greater than 8192 times the frequency resolution. If your circuit contains many Laplace parts which can be combined into a more complex single device, it is generally preferable to do this. This saves computation and memory since there are fewer impulse