4 Mathematical Definition of gm Using differential calculusMaximum gm at VGS =0V:Effect of ID on gm for
5 Very large to assume input terminal approximate an open circuit FET ImpedanceInput Impedance Zi:Very large to assume input terminal approximate an open circuitOutput Impedance Zo:yos: admittance equivalent circuit parameter listed on FET specification sheets.
8 JFET Fixed-Bias Configuration The input is on the gate and the output is on the drain.
9 JFET Fixed-Bias Configuration Once again: same step as BJT to redraw the network to AC equivalent circuit.Capacitor – short circuitDC batteries VGG and VDD are set to zero volts by a short-circuit equivalent
14 Phase RelationshipA CS amplifier configuration has a 180-degree phase shift between input and output.
15 AV ignoring the effects of rd ExampleFixed-bias configuration has an operating point defined by VGSQ = -2V and IDQ = mA, with IDSS = 10mA and VP = -8V. The value of yos is provided as 40 µS. Determine:gmZiZoAVAV ignoring the effectsof rd
44 Voltage GainApplying Kirchhoff’s current law at node b ::
45 Phase RelationshipA CG amplifier configuration has no phase shift between input and output.
46 Depletion-Type MOSFETs D-MOSFETs have similar AC equivalent models.The only difference is that VSGQ can be positive for n-channel devices and negative for p-channel devices.This means that gm can be greater than gm0.