TECHNICAL WORKSHOP MARATHON 2012
CIRCUIT ANALYSIS USING NGSPICE
VISHNU V
2nd Year M.Tech VLSI and Embedded Systems
Govt. Model Engineering College, Thrikkakara
CONTENTS

SIMULATING A CIRCUIT IN NGSPICE

EXAMPLE CIRCUIT

NETLIST CREATION USING gEDA SCHEMATIC EDITOR

ANALYSIS OF BASIC CIRCUITS

HIGH PASS CIRCUIT AND DIFFERENTIATOR

LOW PASS CIRCUIT AND INTEGRATOR

RECTIFIER CIRCUITS

CLIPPER CIRCUITS

CLAMPER CIRCUITS
Simulating a Circuit using NGSPICE
Steps



Mark the nodes present in the circuit using
numbers or symbols (Try to mark Ground node
by '0')
Write the netlist (use texteditors such as gedit or
vi editor etc)for the circuit satisfying all the rules
and regulations.
Save the netlist using .cir or .net extension.
3
Simulating a Circuit using NGSPICE


Open ngspice command window by typing
ngspice in terminal(bash,sash etc)
Give the name of the saved netlist in ngspice
command window.
EXAMPLE CIRCUIT
Simulation of a simple RC filter using NGSPICE
EXAMPLE CIRCUIT

Here there are three nodes




n0
n1
0
Also the components present are



A sinusoidal voltage source
A 3.3nF capacitor
A 1k resistor
Writing NETLIST

Title Line (First Line )
A simple RC High pass filter

Component connections
V1 n0 0 SIN(0 10 1kHz)
C1 n0 n1 3.3nF
R n1 0 1k
Writing NETLIST

Control Lines
.CONTROL
TRAN 0.01ms 10ms
PLOT V(n0) V(n1)

END Lines
.ENDC
.END
Total NETLIST
A Simple RC High pass filter
V1 n0 0 SIN(0 10 1kHz)
C1 n0 n1 3.3nF
R n1 0 1k
.CONTROL
TRAN 0 0.01ms 10ms
PLOT V( n0) V(n1)
.ENDC
.END
SIMULATION STEPS
Save the above file as rc_filter.cir
STEP 1 : Open Terminal and type ngspice
Terminal
Open Terminal and
Type ngspice
Ngspice command
terminal opens
SIMULATION STEPS
STEP 2 : Give the file name of the netlist we have written
ie rc_filter.cir
Give the file name of the
netlist and press enter
SIMULATION STEPS
TRANSIENT ANALYSIS OUTPUT
BASH TERMINAL
WAVE FORM WINDOW
ANALYSIS OF WAVEFORM
Analyse the waveform
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PART II
NETLIST CREATION USING
gEDA SCHEMATIC EDITOR
STEPS
Draw the schematic of the circuit using gEDA
schematic editor


Save the file with extension .sch

Convert .sch file to .net file using gnetlister.
Command :
gnetlist -g spice -o rc_filter.net rc_filter.sch
DRAWING CIRCUIT IN gEDA SCHEMATIC EDITOR
SAVE THE ABOVE SCHEMATIC AS rc_filter.sch
CONVERING SCHEMATIC TO NETLIST
Output File name
Schematic Name
gnetlist -g spice -o rc_filter.net rc_filter.sch
NETLIST OBTAINED FROM SCHEMATIC
rc_filter.net
SIMULATING THE NETLIST
SIMULATING THE NETLIST
Name of the NETLIST
created using gnetlister
SIMULATING THE NETLIST
SIMULATING THE NETLIST : TRANSIENT ANALYSIS
Final Value
Indicates Transient Analysis
Increment value
SIMULATING THE NETLIST : TRANSIENT ANALYSIS
SIMULATING THE NETLIST : TRANSIENT ANALYSIS
PLOT V(2) V(1)
ANALYSIS OF THE WAVEFORM
GREEN COLOUR : INPUT WAVE
RED COLOUR : OUTPUT WAVEFORM
WHY THE AMPLITUDE OF THE
OUTPUT WAVEFORM IS VERY LESS
??
REASONS
The Circuit is a High pass filter, so it passes only high
frequency signals.

We have given an input sinusoidal waveform of
Amplitude = 10V and Frequency = 1kHz


Cut off frequency of the high pass filter is given by,
cutoff frequency= 1/(2*pi*R*C)
Here in this case
Cutoff frequency (3 dB frequency ) = 48.22kHZ
So, Give input sine wave frequency >= 48.22 kHz
MODIFIED NETLIST
A Simple RC High pass filter
V1 n0 0 SIN(0 10 500kHz)
C1 n0 n1 3.3nF
NEW INPUT FREQUENCY
R n1 0 1k
.CONTROL
TRAN 0.0001ms 0.1ms
PLOT n0 n1
.ENDC
.END
OUTPUT WAVEFORM
AC ANALYSIS OF HIGH PASS FILTER
FOR AC ANALYSIS THE CONTROL SIGNAL IS
.AC <sweep type> <points value>
<start frequency> <end frequency>
(sweep type is either
LIN,OCT or DEC)
Examples
.AC LIN 16 60 600KHz
.AC DEC 20 1 10kHz
NETLIST FOR AC ANALYSIS OF HIGH PASS FILTER
A Simple RC High pass filter
V1 n0 0 SIN(0 10 500kHz)
C1 n0 n1 3.3nF
AC ANALYSIS
R n1 0 1k
.CONTROL
AC LIN 1000 0.1Hz 1000kHz
PLOT V(n1)
.ENDC
.END
AC ANALYSIS PLOT I
NETLIST FOR AC ANALYSIS OF HIGH PASS FILTER
A Simple RC High pass filter
V1 n0 0 SIN(0 10 500kHz)
C1 n0 n1 3.3nF
AC ANALYSIS
R n1 0 1k
.CONTROL
AC DEC 10 100Hz 10000kHz
PLOT DB(V(n1)/V(n0))
.ENDC
.END
AC ANALYSIS PLOT II
HOW A HIGH PASS FILTER CAN BE
CONVERTED TO A
DIFFERENTIATOR CIRCUIT
HIGH PASS FILTER AS DIFFERENTIATOR
The Condition in which a high pass filter acts as a
differentiator circuit is given by
RC << 0.0016T ; Where T = Time period of the input
signal
Question ?
Design a Differentiator Circuit which takes a pulse
waveform of frequency 1 kHz and perform its
transient analysis using NGSPICE....
Take the capacitor value as C = 3.3nF
DIFFERENTIATOR TRANSIENT RESPONSE
With RESISTOR VALUE, R = 47k
DIFFERENTIATOR TRANSIENT RESPONSE
With RESISTOR VALUE, R = 10k
RC LOW PASS FILTER
RC LOWPASS FILTER AC ANALYSIS PLOT
RC LOWPASS FILTER AS INTEGRATOR
RECTIFIER CIRCUIT
WRITE THE NETLIST AND PLOT THE WAVEFORMS
RECTIFIER CIRCUIT OUTPUT
CLIPPER
CIRCUITS
POSITIVE CLIPPER
CLIPPING LEVEL : +5V
WRITE NETLIST AND OBTAIN THE OUTPUT WAVEFORM
POSITIVE CLIPPER OUTPUT WAVEFORM
+5V
CLIPPER CIRCUITS
DOUBLE CLIPPER
CLIPPING LEVELS : +5V and -5V
WRITE NETLIST AND OBTAIN THE OUTPUT WAVEFORM
DOUBLE CLIPPER OUTPUT WAVEFORM
+5V
-5V
CLAMPER CIRCUITS
SIMPLE POSITIVE CLAMPER CIRCUIT
OUTPUT WAVEFORM
LAB SESSION
EXPERIMENTS
1. RC HIGH PASS CIRCUIT AND DIFFERENTIATOR
2. RC LOW PASS CIRCUIT AND INTEGRATOR
3. RECTIFIER CIRCUITS
4. CLIPPER CIRCUITS
5. CLAMPER CIRCUITS
ASSIGNMENT I
PLOT THE FOLLOWING WAVEFORM USING NGSPICE
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