Parameter in hspice

Parameters in HSPICE are names that can be assigned numeric values. Its simplest use is to assign a particular value at the beginning of hspice code. If this parameter is used many times in the code, we just need to change the value of the parameter only once and not at all places.

Consider the following example

* Example of .PARAM 
.PARAM impedance =  50
.Tran 50ps 8ns 
.OPTION Post Probe
VIN 1 0 PWL 0 0v 50ps 0v 350ps 3.3v
Rsource 1 2 50
Tfirst 2 0 3 0 ZO=impedance TD=1000ps
C3 4 0 1.5p
Tsecond 3 0 4 0 ZO=impedance TD=1000ps
.Probe v(1) v(2)v(3)v(4)

This is a simple hspice code with two sections of transmission line. Each transmission line has typical impedance. The value of this impedance has been assigned a value of 50 at the beginning of the code with the statement .PARAM impedance = 50 If we need to change the value of the impedance of the transmission line, we need to make change only at one place, instead of two places. If you are curious, what the above hspice code does, take a look at the waveforms below. It is a simple source termination reflected wave propagation scheme. The effect of the capacitor reflection is not visible as it gets absorbed at the source.

Figure - Illustration of Use of .PARAM simple reflected wave

In the next page we will learn about sweeping the parameters in hspice.