User Guide

Chapter 6 Analog behavioral modeling
162
value that can be assigned to the part’s DELAY property
for subsequent runs, without otherwise altering the table.
The output of the part depends on the analysis being
done. For DC and bias point, the output is the zero
frequency magnitude times the input voltage. For AC
analysis, the input voltage is linearized around the bias
point (similar to EVALUE and GVALUE parts, Modeling
mathematical or instantaneous relationships on page 6-176).
The output for each frequency is then the input times the
gain, times the value of the table at that frequency.
For transient analysis, the voltage is evaluated at each
time point. The output is then the convolution of the past
values with the impulse response of the frequency
response. These rules follow the standard method of using
Fourier transforms. We recommend looking at one or
more of the references cited in Frequency-domain device
models on page 6-181 for more information.
Note The table’s frequencies must be in order from lowest to highest. The
TABLE part provides one input and one output.
Example
A device, ELOFILT, is used as a frequency filter. The input
to the frequency response is the voltage at net 10. The
output is a voltage across nets 5 and 0. The table describes
a low pass filter with a response of 1 (0 dB) for frequencies
below 5 kilohertz and a response of 0.001 (-60 dB) for
frequencies above 6 kilohertz. The phase lags linearly with
frequency. This is the same as a constant time delay. The
delay is necessary so that the impulse response is causal.
That is, so that the impulse response does not have any
significant components before time zero. The FTABLE
part in Figure 39 could be used.
Figure 39 FTABLE part example.
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