1. CIRCUIT ANALYSIS USING NGSPICE
TECHNICAL WORKSHOP MARATHON 2012
CIRCUIT ANALYSIS USING NGSPICE
VISHNU V
2nd Year M.Tech VLSI and Embedded Systems
Govt. Model Engineering College, Thrikkakara

2. 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

3. 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

4. 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.

5. EXAMPLE CIRCUIT
Simulation of a simple RC filter using NGSPICE

6. EXAMPLE CIRCUIT Here there are three nodes n0 n1
Also the components present are
A sinusoidal voltage source
A 3.3nF capacitor
A 1k resistor

7. 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 n k

8. Writing NETLIST Control Lines .CONTROL TRAN 0.01ms 10ms
PLOT V(n0) V(n1)
END Lines
.ENDC
.END

9. Total NETLIST A Simple RC High pass filter V1 n0 0 SIN(0 10 1kHz)
C1 n0 n1 3.3nF
R n k
.CONTROL
TRAN ms 10ms
PLOT V( n0) V(n1)
.ENDC
.END

10. SIMULATION STEPS Save the above file as rc_filter.cir
Terminal
Save the above file as rc_filter.cir
STEP 1 : Open Terminal and type ngspice
Open Terminal and Type ngspice
Ngspice command terminal opens

11. 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

12. SIMULATION STEPS BASH TERMINAL WAVE FORM WINDOW
TRANSIENT ANALYSIS OUTPUT
BASH TERMINAL
WAVE FORM WINDOW

13. ANALYSIS OF WAVEFORM
Analyse the waveform I N P U T
OUTPUT

14. NETLIST CREATION USING
PART II
NETLIST CREATION USING
gEDA SCHEMATIC EDITOR

15. 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

16. DRAWING CIRCUIT IN gEDA SCHEMATIC EDITOR
SAVE THE ABOVE SCHEMATIC AS rc_filter.sch

17. CONVERING SCHEMATIC TO NETLIST
Output File name
Schematic Name
gnetlist -g spice -o rc_filter.net rc_filter.sch

18. NETLIST OBTAINED FROM SCHEMATIC
rc_filter.net

19. SIMULATING THE NETLIST

20. SIMULATING THE NETLIST
Name of the NETLIST created using gnetlister

21. SIMULATING THE NETLIST

22. SIMULATING THE NETLIST : TRANSIENT ANALYSIS
Final Value
Indicates Transient Analysis
Increment value

23. SIMULATING THE NETLIST : TRANSIENT ANALYSIS

24. SIMULATING THE NETLIST : TRANSIENT ANALYSIS
PLOT V(2) V(1)

25. ANALYSIS OF THE WAVEFORM
GREEN COLOUR : INPUT WAVE
RED COLOUR : OUTPUT WAVEFORM

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

27. Cut off frequency of the high pass filter is given by,
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 >= kHz

28. A Simple RC High pass filter V1 n0 0 SIN(0 10 500kHz) C1 n0 n1 3.3nF
MODIFIED NETLIST
A Simple RC High pass filter
V1 n0 0 SIN( kHz)
C1 n0 n1 3.3nF
R n k
.CONTROL
TRAN ms 0.1ms
PLOT n0 n1
.ENDC
.END
NEW INPUT FREQUENCY

29. OUTPUT WAVEFORM

30. 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  KHz
.AC  DEC  20 1  10kHz

31. NETLIST FOR AC ANALYSIS OF HIGH PASS FILTER
A Simple RC High pass filter
V1 n0 0 SIN( kHz)
C1 n0 n1 3.3nF
R n k
.CONTROL
AC LIN Hz 1000kHz
PLOT V(n1)
.ENDC
.END
AC ANALYSIS

32. AC ANALYSIS PLOT I

33. NETLIST FOR AC ANALYSIS OF HIGH PASS FILTER
A Simple RC High pass filter
V1 n0 0 SIN( kHz)
C1 n0 n1 3.3nF
R n k
.CONTROL
AC DEC Hz kHz
PLOT DB(V(n1)/V(n0))
.ENDC
.END
AC ANALYSIS

34. AC ANALYSIS PLOT II

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

36. HIGH PASS FILTER AS DIFFERENTIATOR
The Condition in which a high pass filter acts as a differentiator circuit is given by
RC << T ; 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

37. DIFFERENTIATOR TRANSIENT RESPONSE
With RESISTOR VALUE, R = 47k

38. DIFFERENTIATOR TRANSIENT RESPONSE
With RESISTOR VALUE, R = 10k

39. RC LOW PASS FILTER

40. RC LOWPASS FILTER AC ANALYSIS PLOT

41. RC LOWPASS FILTER AS INTEGRATOR

42. RECTIFIER CIRCUIT
WRITE THE NETLIST AND PLOT THE WAVEFORMS

43. RECTIFIER CIRCUIT OUTPUT

44. CLIPPER CIRCUITS POSITIVE CLIPPER CLIPPING LEVEL : +5V
WRITE NETLIST AND OBTAIN THE OUTPUT WAVEFORM

45. POSITIVE CLIPPER OUTPUT WAVEFORM

46. CLIPPER CIRCUITS DOUBLE CLIPPER CLIPPING LEVELS : +5V and -5V
WRITE NETLIST AND OBTAIN THE OUTPUT WAVEFORM

47. DOUBLE CLIPPER OUTPUT WAVEFORM

48. CLAMPER CIRCUITS
SIMPLE POSITIVE CLAMPER CIRCUIT

49. OUTPUT WAVEFORM

50. LAB SESSION EXPERIMENTS RC HIGH PASS CIRCUIT AND DIFFERENTIATOR
RC LOW PASS CIRCUIT AND INTEGRATOR
RECTIFIER CIRCUITS
CLIPPER CIRCUITS
CLAMPER CIRCUITS

51. PLOT THE FOLLOWING WAVEFORM USING NGSPICE
ASSIGNMENT I
PLOT THE FOLLOWING WAVEFORM USING NGSPICE

52. 52