CIRCUIT ANALYSIS USING NGSPICE VISHNU V 2 nd Year M.Tech VLSI and Embedded Systems Govt. Model Engineering College, Thrikkakara TECHNICAL WORKSHOP MARATHON.

CIRCUIT ANALYSIS USING NGSPICE

VISHNU V

2nd Year M.Tech VLSI and Embedded Systems

Govt. Model Engineering College, Thrikkakara

TECHNICAL WORKSHOP MARATHON 2012

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

3

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.

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 3.3nFR n1 0 1k

Writing NETLIST

Control Lines

.CONTROLTRAN 0.01ms 10msPLOT V(n0) V(n1)

END Lines

.ENDC

.END

A Simple RC High pass filterV1 n0 0 SIN(0 10 1kHz)C1 n0 n1 3.3nFR n1 0 1k.CONTROLTRAN 0 0.01ms 10msPLOT V( n0) V(n1).ENDC.END

Total NETLIST

SIMULATION STEPS

Open Terminal and Type ngspice

Save the above file as rc_filter.cir STEP 1 : Open Terminal and type ngspice

Ngspice command terminal opens

Terminal

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

WAVE FORM WINDOWBASH TERMINAL

SIMULATION STEPS

Analyse the waveform

INPUT

ANALYSIS OF WAVEFORM

OUTPUT

PART II

NETLIST CREATION USING gEDA SCHEMATIC EDITOR

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

STEPS

SAVE THE ABOVE SCHEMATIC AS rc_filter.sch

DRAWING CIRCUIT IN gEDA SCHEMATIC EDITOR

gnetlist -g spice -o rc_filter.net rc_filter.sch

Output File name Schematic Name

CONVERING SCHEMATIC TO NETLIST

rc_filter.net

NETLIST OBTAINED FROM SCHEMATIC

SIMULATING THE NETLIST

Name of the NETLIST created using gnetlister

SIMULATING THE NETLIST

SIMULATING THE NETLIST

Indicates Transient AnalysisIncrement value

Final Value

SIMULATING THE NETLIST : TRANSIENT ANALYSIS

SIMULATING THE NETLIST : TRANSIENT ANALYSIS

PLOT V(2) V(1)

SIMULATING THE NETLIST : TRANSIENT ANALYSIS

GREEN COLOUR : INPUT WAVERED COLOUR : OUTPUT WAVEFORM

ANALYSIS OF THE WAVEFORM

WHY THE AMPLITUDE OF THE OUTPUT WAVEFORM IS VERY LESS ??

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

REASONS

A Simple RC High pass filterV1 n0 0 SIN(0 10 500kHz)C1 n0 n1 3.3nFR n1 0 1k.CONTROLTRAN 0.0001ms 0.1msPLOT n0 n1.ENDC.END

MODIFIED NETLIST

NEW INPUT FREQUENCY

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 filterV1 n0 0 SIN(0 10 500kHz)C1 n0 n1 3.3nFR n1 0 1k.CONTROLAC LIN 1000 0.1Hz 1000kHzPLOT V(n1).ENDC.END

AC ANALYSIS

AC ANALYSIS PLOT I

NETLIST FOR AC ANALYSIS OF HIGH PASS FILTER

A Simple RC High pass filterV1 n0 0 SIN(0 10 500kHz)C1 n0 n1 3.3nFR n1 0 1k.CONTROLAC DEC 10 100Hz 10000kHzPLOT DB(V(n1)/V(n0)).ENDC.END

AC ANALYSIS

AC ANALYSIS PLOT II

HOW A HIGH PASS FILTER CAN BE CONVERTED TO A DIFFERENTIATOR CIRCUIT

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

HIGH PASS FILTER AS DIFFERENTIATOR

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

r

-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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