Chapter Five The Field-Effect Transistor

Figure 6—2 A three-terminal nonlinear device that can be controlled by the voltage at the third terminal v G : (a) biasing circuit; (b) I–V characteristic and load line. If v G = 0.5 V, the d-c values of I D and V D are as shown by the dashed lines.

Figure 6—3 Simplified cross-sectional view of a junction FET: (a) transistor geometry; (b) detail of the channel and voltage variation along the channel with V G = 0 and small I D.

Figure 6—4 Depletion regions in the channel of a JFET with zero gate bias for several values of V D : (a) linear range; (b) near pinch-off; (c) beyond pinch-off.

Figure 6—5 Effects of a negative gate bias: (a) increase of depletion region widths with V G negative; (b) family of current– voltage curves for the channels as V G is varied.

Figure 6—11 n-channel MOSFET cross-sections under different operating conditions: (a) linear region for V G > V T and V D V T and V D = (V G 2 V T ); (c) strong saturation, V G > V T and V D > (V G 2 V T ).

Figure 6—27 Drain current–voltage characteristics for enhancement transistors: (a) for n-channel V D, V G, V T, and I D are positive; (b) for p-channel all these quantities are negative.

Figure 6—28 Linear region transfer characteristics: (a) plot of drain current versus gate voltage for MOSFETs in the linear region; (b) transconductance as a function of gate bias.

Figure 6—29 Saturation region transfer characteristics: plot of square root of the drain current versus gate voltage for MOSFETs.

Figure 6—39 Equivalent circuit of a MOSFET, showing the passive capacitive and resistive components. The gate capacitance C i is the sum of the distributed capacitances from the gate to the source-end of the channel (C GS ) and the drain-end (C GD ). In addition, we have an overlap capacitance (where the gate electrode overlaps the source/drain junctions) from the gate-to-source (C OS ) and gate-to-drain (C OD ). C OD is also known as the Miller overlap capacitance. We also have p-n junction depletion capacitances associated with the source (C JS ) and drain (C JD ). The parasitic resistances include the source/drain series resistances (R S and R D ), and the resistances in the substrate between the bulk contact and the source and drain (R BS and R BD ). The drain current can be modeled as a (gate) voltage-controlled constant-current source.

Figure 5.24 (a) An NMOS common-source circuit and (b) the NMOS circuit for Example 5.3

Figure 5.25 (a) A PMOS common-source circuit, (b) results when saturation-region bias assumption is incorrect, and (c) results when nonsaturation-region bias assumption is correct

Figure 5.28 Transistor characteristics, v DS (sat) curve, load line, and Q-point for the NMOS common-course circuit in Figure 5.24 (b)

Figure 5.29 NMOS common-source circuit with source resistor

Figure 5.35 Circuit with enhancement load devices and NMOS driver

Figure 5.36 Voltage transfer characteristics of NMOS inverter with enhancement load device

Figure 5.37 (a) Depletion-mode NMOS device with the gate connected to the source and (b) current-voltage characteristics

Figure 5.39 Circuit with depletion load device and NMOS driver

Figure 5.40 Voltage transfer characteristics of NMOS inverter with depletion load device

Figure 5.47 (a) An NMOS common-source circuit with a time-varying signal coupled to the gate and (b) transistor characteristics, load line, and superimposed sinusoidal signals

Chapter Six Basic FET Amplifiers

Figure 6.13 Common-source circuit with voltage divider biasing and coupling capacitor

Figure 6.14 Small-signal equivalent circuit, assuming coupling capacitor acts as a short circuit

Figure 6.17 DC load line and transition point for NMOS circuit shown in Figure 6.16

Figure 6.19 Small-signal equivalent circuit of NMOS common-source amplifier with source resistor

Figure 6.28 NMOS source-follower or common-drain amplifier

Figure 6.29 (a) Small-signal equivalent circuit of NMOS source-follower and (b) small-signal equivalent circuit of NMOS source-follower with all signal grounds at a common point

Figure 6.34 Common-gate circuit

Figure 6.35 Small-signal equivalent circuit of common-gate amplifier

Figure 6.39 (a) NMOS amplifier with enhancement load device; (b) driver transistor characteristics and enhancement load curve with transition point

Figure 6.39c Voltage transfer characteristics of NMOS amplifier with enhancement load device

Figure 6.43 (a) NMOS amplifier with depletion load device; (b) driver transistor characteristics and depletion load curve, with transition points

Figure 6.43c (c) voltage transfer characteristics

Figure 6.45 (a) CMOS common-source amplifier; (b) PMOS active load i-v characteristic, (c) driver transistor characteristics with load curve, (d) voltage transfer characteristics

Figure 6.50 NMOS cascode circuit

Figure 6.52 Small-signal equivalent circuit of NMOS cascode circuit