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 –Ex. R –Names should not contain comma, space, or =, or parenthesis Capacitor –C –Ex CBYP uF Inductor –L

Units in PSpice T = tera = G = giga = 10 9 Meg = mega = 10 6 k = kilo 10 3 m = milli = u = micro = n = nano = p = pico = f = femto =

Source design Independent Voltage Source –V –VCC 10 0 DC 6 Independent Current Source –I –I_in 10 0 AC 3m

Voltage Sources DC: Vname n+ n- DC AC: Vname n+ n- AC 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.model QPNP PNP(Is=650.6E-18 Xti=3 Eg=1.11 Vaf=100 Bf=150 Ne= Ise=54.81f Ikf=1.079 Xtb=1.5 Br=3.563 Nc=2 Isc=0 Ikr=0 Rc= 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= 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 –Ex. Q npn MOSFET: –M –M nmos –M pmos L=10u W=5u AD=100p AS=100p PD=40u PS=40u

Building a circuit First, draw the diagram Label nodes Code in Pspice

Code

Analysis Types DC Analysis –DC transfer curve source and sweep.dc [src2 start2 stop2 incr2].DC VIN DC VDS VGS –“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 ) –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 IDID G D S

Solution: 1) Draw circuit with sources 2) Label nodes! 3) Code in spice 3 0 2

Solution:

Graph

Inverter demonstration

Results