Pspice Tutorial

PSpice Tutorial

October 13, 2004 Franklin Chiang

Orcad Programs • PSpice – Use “netlists” to code up circuits. Text based. – Start  programs  Orcad Family Release 9.2  Orcad PSpice

• Capture – Use diagrams to draw up circuits and simulate. Graphics based. – Start  programs  Orcad Family Release 9.2 Lite Capture Lite

Startup and Basic Syntax • Start  Programs  Orcad Release 9.2  PSpice • File  New  Text file • 5 different “commands” you can use – – – – –

Title: first line of code (always) .END: last line of code (always) Comment: line denoted by * Element: Resistor, capacitor, etc. Control: analysis

Passive Component Description • Resistor

– R <node1> <node2> – Ex. R1 1 2 100 – Names should not contain comma, space, or =, or parenthesis

• Capacitor

– C <node1> <node2> – Ex CBYP 13 0 1uF

• Inductor

– L <node1> <node2>

Units in PSpice • • • • • • • • •

T = tera = 1012 G = giga = 109 Meg = mega = 106 k = kilo 103 m = milli = 10-3 u = micro = 10-6 n = nano = 10-9 p = pico = 10-12 f = femto = 10-15

Source design • Independent Voltage Source – V <+node> <-node> – VCC 10 0 DC 6

• Independent Current Source – I <+node> <-node> – I_in 10 0 AC 3m

Voltage Sources • DC: Vname n+ n- DC • AC: Vname n+ n- AC <magnitude> • Transient: – Vname n+ n- sin(Vo Va freq td damp) – Vname n+ n- pulse(V1 V2 td tr tf PW T) – Vname n+ n- PWL(t1, v1, t2, v2, …, tn, vn)

Active Devices (transistors!) • Usually given a model file as text file • Include it into pspice using: – .lib – ex: .lib 115cmodel.txt

• Make sure text file is in same directory

Including your own model files • .model <parameters….> • .model QPNP PNP(Is=650.6E-18 Xti=3 Eg=1.11 Vaf=100 Bf=150 Ne=1.829 + Ise=54.81f Ikf=1.079 Xtb=1.5 Br=3.563 Nc=2 Isc=0 Ikr=0 Rc=.715 + Cjc=14.76p Mjc=.5383 Vjc=.75 Fc=.5 Cje=19.82p Mje=.3357 Vje=.75 + Tr=111.3n Tf=603.7p Itf=.65 Vtf=5 Xtf=1.7 Rb=10) • .model QNPN NPN(Is=14.34f Xti=3 Eg=1.11 Vaf=100 Bf=150 Ne=1.307 + Ise=14.34f Ikf=.2847 Xtb=1.5 Br=6.092 Nc=2 Isc=0 Ikr=0 Rc=1 + Cjc=7.306p Mjc=.3416 Vjc=.75 Fc=.5 Cje=22.01p Mje=.377 Vje=.75 + Tr=46.91n Tf=411.1p Itf=.6 Vtf=1.7 Xtf=3 Rb=10) • Copy, paste.

Declaring transistors • BJT: – Q <model> – Ex. Q23 10 24 13 npn

• MOSFET: – M <model> – M1 24 2 0 20 nmos – M2 2 9 3 0 pmos L=10u W=5u AD=100p AS=100p PD=40u PS=40u

Building a circuit

R 1 1k

1

• First, draw the diagram • Label nodes 10V dc • Code in Pspice

2

R2

R3

3k

5k

V 1

3

3 R4

R5

3k

4k

R 6

0

2k

4

Code

Analysis Types • DC Analysis – DC transfer curve source and sweep • .dc <source> [src2 start2 stop2 incr2] • .DC VIN 0.25 5.0 0.25 • .DC VDS 0 10 .5 VGS 0 5 1 – “nested sweep”: for each VDS, sweep VGS from 0 to 5 incrementing by 1 each time. So total number of operations would be 20 * 5 = 100

Analysis Types • Operating Point – .op – Calculates dc operating point of circuit with inductors shorted and capacitors open. – Useful in checking your work. – Results put in .txt file

Analysis types • AC small signal – computes the ac output variables as a function of frequency – first computes the dc operating point of the circuit and determines linearized, small-signal models for all of the nonlinear devices in the – resultant linear circuit is then analyzed over a user-specified range of frequencies – Can be used to compute noise!

Analysis Types • AC Analysis (cont) – .AC DEC ND FSTART FSTOP • Dec = decade variation, ND = pts. / decade

– .AC LIN NP FSTART FSTOP • Lin = linear variation, NP = # pts

– .NOISE OUTV INSRC NUMS • OUTV = output voltage which defines summing point • INSRC = name of independent source which is the noise input reference • NUMS = summary interval

Analysis Types • Transient (.tran <step> <stop> <start>) – The transient analysis portion of SPICE computes the transient output variables as a function of time over a user specified time interval – The initial conditions are automatically determined by a dc analysis – Useful for 115C – .tran 1ns 1000ns 500ns

Back to Resistor Bridge •

Ex. Find voltage across R3 when Vin = 10V

Results

Transistor examples: IV curve • Plot I-V characteristic of NMOS with: – W = 1.2um – L = 0.25 um – Set Vdd = Vg = 2.5V, Vs = 0V

D G

M1

ID

S

Solution: 3

• 1) Draw circuit with sources • 2) Label nodes! • 3) Code in spice

V 2 2 .5

2

M1 V 3

2 .5

0

Solution:

Graph

Inverter demonstration

Results