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Q — Bipolar Junction Transistor (BJT)

The BJT is a three-terminal semiconductor device used for amplification and switching.

Syntax

Q<name> <collector> <base> <emitter> <model_name> [<area>] [OFF] [IC=<vbe>[,<vce>]]
Parameter Description
collector Collector node
base Base node
emitter Emitter node
model_name Name of a .MODEL NPN(...) or .MODEL PNP(...) definition
area Area factor
OFF Initial guess: device is off
IC=vbe[,vce] Initial junction voltages for UIC

Examples

Q1 C B E 2N3904
Q2 OUT BASE 0 NPN_MODEL 2.0
Q3 C B E PNP_MOD IC=0.7,5.0

Model Definition

NPN

.MODEL 2N3904 NPN(Is=6.734f Bf=416.4 Br=0.7374 Cje=3.638p Cjc=4.493p)

PNP

.MODEL 2N3906 PNP(Is=1.41f Bf=180 Br=4 Cje=9.7p Cjc=18p)

Common Model Parameters

Parameter Description
Is Transport saturation current
Bf Ideal forward current gain (β)
Br Ideal reverse current gain
Nf Forward current emission coefficient
Nr Reverse current emission coefficient
Cje Base-emitter zero-bias capacitance
Cjc Base-collector zero-bias capacitance
Vaf Forward Early voltage
Var Reverse Early voltage
Rb Base resistance
Rc Collector resistance
Re Emitter resistance

Typical Usage

Common-emitter amplifier
VCC VCC 0 12
V1 IN 0 DC 0 AC 1m
R1 VCC OUT 4.7k
R2 IN BASE 100k
R3 BASE 0 22k
Q1 OUT BASE 0 2N3904
.model 2N3904 NPN(Is=6.734f Bf=416.4)
.AC DEC 10 10 10MEG
.SAVE V(OUT)
.END