What is Spice?
SPICE is a general-purpose circuit simulation program for nonlinear dc, nonlinear transient, and linear ac analyses. Circuits may contain resistors, capacitors, inductors, mutual inductors, independent voltage and current sources, four types of dependent sources, lossless and lossy transmission lines (two separate implementations), switches, uniform distributed RC lines, and the five most common semiconductor devices: diodes, BJTs, JFETs, MESFETs, and MOSFETs.

How does Spice Work?
Basically, SPICE operates like this:

1. Describe a circuit in a text file (..cir. extension) called a netlist. Use your favorite text editor (edit, nano, emacs, kwrite, joe, vim, pico, etc. ) to write netlist file.

   	R circuit
   	*First line is the circuit name, and it is compulsory
   	*The lines that start with star character '*' are comment lines and they are ignored by Spice 
   	*V and R reserved characters for voltage source and resistors.
   	*Spice is not case sensitive. The upper-case and lower-case letters are considered same.
   	VS 1 0 dc 10V
   	R1 1 2 5k
   	r2 2 3 6k
   	r3 2 0 4k
   	R4 3 0 9k
   	.tran 0.1 ms 0.1s 
   	.END
   

2. Save the file with extention "cir" as "simpleR.cir"
3. Run a simulation. SPICE reads the netlist and then performs the requested analysis: AC, DC, or Transient Analysis. The results are stored in a binary data file.

   	To launch the ngspice use command ngspice
   	$ ngspice
   	ngspice 1 ->  
   	To simulate "simpleR.cir" file use command "aspice"
   	
   	ngspice 1 -> aspice simpleR.cir
   	
   	To see varibles use command "display"
   	
   	ngspice 2 -> display
   	
   	Here are the vectors currently active:
   	
   	Title: R circuit
   	Name: tran1 (Transient Analysis)
   	Date: Thu Jan 29 10:38:41  2009
   	
   	V(1)                : voltage, real, 60 long
   	V(2)                : voltage, real, 60 long
   	V(3)                : voltage, real, 60 long
   	time                : time, real, 60 long [default scale]
   	vs#branch           : current, real, 60 long
   

The most used commands in Ngspice

	aspice: Start a Spice run, and when it is finished load the resulting data.
	
	display: Prints a summary of currently defined vectors.
	
	edit: Print the current Spice input file into a file,
              call up the editor on that file and allow the user to modify it,
              and then read it back in, replacing the original file.
	
	print: Prints the vector 
	       Example: print v(2)
	
	plot: Plot the given exprs on the screen
	      Example: plot v(2)-v(3)
	
	For more information type "help"

Some useful links
ngspice can be dowloaded from: http://sourceforge.net/project/showfiles.php?group_id=38962

Ngspice manual:
http://newton.ex.ac.uk/teaching/CDHW/Electronics2/userguide/
http://www.seas.upenn.edu/~jan/spice/spice.overview.html
http://bwrc.eecs.berkeley.edu/Classes/IcBook/SPICE/

Hasari Karci
29/01/2009