User Guide

PSpice-equivalent parts
185
Figure 53 shows an EFREQ device used as a low pass
filter. The input to the frequency response is the voltage
across the input pins. The table describes a low pass filter
with a response of 1 (0 dB) for frequencies below 5
kilohertz and a response of .001 (-60 dB) for frequencies
above 6 kilohertz. The output is a voltage across the
output pins.
This part is defined by the following properties:
TABLE = (0, 0, 0) (5kHz, 0, -5760) (6kHz, -60, -6912)
DELAY =
R_I =
MAGUNITS =
PHASEUNITS =
Since R_I, MAGUNITS, and PHASEUNITS are undefined,
each table entry is interpreted as containing frequency,
magnitude value in dB, and phase values in degrees.
Delay defaults to 0.
The phase lags linearly with frequency meaning that this
table exhibits a constant time (group) 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 constant group delay is calculated from the values for
a given table entry as follows:
group delay = phase / 360 / frequency
For this example, the group delay is 3.2 msec
(6912 / 360 / 6k = 5760 / 360 / 6k = 3.2m). An alternative
specification for this table could be:
TABLE = (0, 0, 0) (5kHz, 0, 0) (6kHz, -60, 0)
DELAY = 3.2ms
R_I =
MAGUNITS =
PHASEUNITS =
This produces a PSpice netlist declaration like this:
ELOWPASS 5 0 FREQ {V(10)} = (0,0,0) (5kHz,0,0) (6kHz-60,0)
+ DELAY = 3.2ms
Figure 53 EFREQ part example.
Pspug.book Page 185 Wednesday, November 11, 1998 1:14 PM