IV-3HOIV-3. MESFET and Devices Parameters
(1) GaAs MESFET 1 x 250 m MESFET
Ci : Gate-to-Source capacitance ~ 0.3 pF ri : Charging resistance of Ci ~ 25 Cgd : Gate-to-Drain capacitance ~ 0.02 pF
Cgd
jωτ gmVe
Ls
Rg
Lg
Ld
V
+
Cgs
Rs
Ri
Cds : Drain-to-Source capacitance ~ 0.05 pF
Rd
rds : Drain-to-Source resistance ~ 600 gm : transconductance ~ 40 mS
gds Cds
fT ≈
gm 2πCi
fT =
1 2πτ c
=
vs 2πL
τc =
L vs
f max
f = T 2
rds 33 x 103 ri L
ICE651 MMIC Design
IV-3-1
IV-3. MESFET and Devices Parameters
(2) Measured S-Parameters
S11 : R-C serial circuit small with zero Cgd
Constant resistant circle
S12 : small because of small Cgd S21 : input voltage btn Cgs at low f
decreased voltage btn Cgs at hier f
S22 : R-C parallel circuit
Constant conductance circle High f : increased……
