The following formulas are meant as a reminder of the fundamentals given in most standard electronics textbooks. Notation for the formulas have the traditional meanings. Depletion capacitances are all given with a negative sign in the denominator as in C = C₀/(1 − V/ϕ)^γ. Consequently, when the junction is reverse biased, the minus sign turns into a positive sign. Figure F.1 presents the basic FET features and symbols. The transistor body terminal typically is connected to the source or to ground. When the source is not grounded, the body effect modifies the transistor properties. The equations using the Early voltage, V_A, should conform with the sign convention used by SPICE (V_A > 0).

BIPOLAR TRANSISTOR PARAMETERS (BJT)

Description	Formula
Collector current
Transconductance
Input resistance
Output resistance
Base charging capacitance	CD = τFgm
Emitter–base junction
Input capacitance	Cπ = Cb + Cje
Collector base
Collector substrate
Transition frequency
Thermal voltage

JUNCTION FIELD-EFFECT TRANSISTOR PARAMETERS (JFET)

Description	Formula
Saturated drain current
	VDS ≥ VGS − VP
Ohmic region drain current
	VDS < VGS − VP
Transconductance
Output resistance
Gate–source capacitance
Gate–drain capacitance
Gate–substrate capacitance
n-Channel JFET	VP < 0
p-Channel JFET	VP > 0

METAL–OXIDE SEMICONDUCTOR FIELD-EFFECT TRANSISTOR (MOSFET) PARAMETERS

Description	Formula
Saturation region drain current
	VDS ≥ VGS − Vt
Ohmic region drain current
	VDS < VGS − Vt
Oxide capacitance
Transconductance
Output resistance
Input capacitance	Cin = CGS + CGD = CoxLW
Transition frequency
Surface mobility holes	μs = 200 cm2/V−s
Surface mobility electrons	μs = cm2/V−s
n-Channel JFET	p-Channel JFET
IDSS > 0	IDSS < 0
VP < 0	VP > 0
VP < VGS for |IDS| > 0	VGS < VP for |IDS| > 0
NMOS Enhancement	PMOS Enhancement
Vt > 0	Vt < 0
V GS > V t	V GS < V t
NMOS Depletion	PMOS Depletion
Vt < 0	Vt > 0
VGS > Vt < 0 for |IDS| > 0	VGS < Vt for |IDS|

SMALL-SIGNAL SINGLE-TRANSISTOR AMPLIFIER CONFIGURATIONS

MOSFET	BJT
Common Source	Common Emitter
Rin = RB = R1R2	Rin = (rπ + rb)RB ≈ rπ
Rout = RDro	Rout = Rcro
	AV = −gm (RcroRL)
Source Degeneration	Emitter Degeneration
Rin = RB = R1R2	Rin = RB[rπ + RE (β + 1)]
	≈ rπ (1 + gmRE)
Rout = ro[1 + (gm + gmb)RS] + RS	Rout = RErπ + ro [1 + gm (rπRE)]
	≈ ro (1 + gmRE)
Common Gate	Common Base
Rout = RD[ro + Rgen + Rgenro (gm + gmb)]
Gm = gm + gmb
	AV = gm (RC|RL)
Common Drain (Source Follower)	Common Collector (Emitter Follower)
Rin = R1R2	Rin = RB[rπ + rb + (β + 1)(roRE)]