{"id":1384,"date":"2012-09-04T09:11:12","date_gmt":"2012-09-04T07:11:12","guid":{"rendered":"http:\/\/raftaman.net\/?p=1384"},"modified":"2021-05-15T11:46:39","modified_gmt":"2021-05-15T09:46:39","slug":"simulating-a-lowpass-filter-with-geda-and-ngspice","status":"publish","type":"post","link":"https:\/\/possiblelossofprecision.net\/?p=1384","title":{"rendered":"Simulating a lowpass filter with gEDA and ngspice"},"content":{"rendered":"

Getting started with ngspice<\/a> can be quite tricky. It’s a very powerful piece of software and although the user manual<\/a> is quite comprehensive, its complexity can easily scare off beginners.
\nHere’s a simple step-by-step tutorial on how to simulate a very simple electronic circuit. It should enable you to run your own simulations of circuits you designed.<\/p>\n

<\/p>\n

Creating the circuit<\/h2>\n

The sample circuit is a lowpass RC filter. It’s simple, contains a reasonable amount of components and yet we can do different types of analysis. I assume, you already know how to use gschem<\/a>. If not, have a look at the gEDA wiki<\/a> for a list of tutorials.<\/p>\n

Start up gschem<\/code> and draw the following circuit:<\/p>\n

\"\"<\/a>

Simple lowpass RC filter<\/p><\/div>\n

Of course, you can name your buses differently. I chose n0<\/em> and n1<\/em> here. The bus named 0<\/em> is mandatory<\/strong> as it specifies the reference (ground) net.<\/p>\n

V1<\/em> is an independent AC voltage source. It’s parameters are wave form (sin<\/em>), voltage offset in Volts (0[V]<\/em>), amplitude in Volts (1[V]<\/em>) and frequency (200kHz<\/em>).<\/p>\n

Save the schematic as rcSIN.sch<\/a>.<\/p>\n

Generating the netlist<\/h2>\n

SPICE doesn’t use gschem schematics as input but so-called netlists. To generate a netlist file from a schematic, gnetlist<\/code> can be used:<\/p>\n

\r\n$ gnetlist -g spice -o rcSIN.net rcSIN.sch \r\nCommand line passed = gnetlist -g spice -o rcSIN.net rcSIN.sch \r\nLoading schematic [rcSIN.sch]\r\n<\/pre>\n
The resulting rcSIN.net<\/a> should look like this:<\/p>\n
\r\n* Spice netlister for gnetlist\r\nR1 n1 n0 10k\r\nC1 n1 0 1nF\r\nV1 n0 0 sin(0 1 200kHz)\r\n.END\r\n<\/pre>\n
The file is quite self-explanatory: Each line contains a single component, the first column of each line the component’s reference designator, the subsequent columns the netnames for each pin and finally the value attribute.<\/p>\n
Running a transient simulation<\/h2>\n
SPICE can run different types of analysis, e.g.<\/p>\n