0195136047.pdf

416 TRANSISTOR AMPLIFIERS

+

−

VCC

RB RC

Figure P8.1.3

+

−

VCC

RB

RC

Figure P8.1.4

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−

VCC = 24 V

30,000 Ω

9000 Ω

I 1

I 2 750 Ω

1500 Ω

Figure P8.1.5

VDD=24 V and for the JFETVP= 3 .5 V and

IDSS=5 mA.

8.2.2Ann-channel JFET havingVP = 3 .5 V and

IDSS=5 mA is biased by the circuit of Figure

8.2.1 withVDD =28 V,RS = 3000 , and

R 2 =100 k. If the operating point is given by

IDQ=2 mA andVDSQ=12 V, determineVG,

RD, andR 1.

*8.2.3A self-biasing method for the JFET is shown in
Figure P8.2.3. The JFET hasVP = 3 V and
IDSS =24 mA. It is to operate at an active-
regionQpoint that is given byIDQ=5mAand
VDSQ=8 V. DetermineRSandRDso that the
desiredQpoint is achieved withVDD=16 V.
8.2.4Ann-channel depletion MOSFET that hasVP= 3
V andIDSS=3 mA (whenVDS=10 V) is biased
by the circuit of Figure 8.2.1 withVDD=20 V
andR 2 =1M. If the operating point is given
byIDQ=3mAandVDSQ=10 V, and 40% of
the voltage drop acrossRDandRSis acrossRS,
determineRS,RD,VG, andR 1.

8.2.5Given that ann-channel enhancement MOSFET

hasVT = 1 .5V,K =5 mA/V^2 ,IDQ= 10

mA,VDSQ=15 V, and a maximum continuous

power dissipation of 0.3 W. For the biasing circuit

of Figure 8.2.2 withVDD=24 V,R 2 =1M,

and the voltage acrossRS=3V,findRS,RD,VG,

andR 1. Also find the continuous power dissipated

in the MOSFET.

*8.3.1By analyzing the small-signal ac equivalent circuit

of the CE BJT amplifier shown in Figure 8.3.1(b),

show that Equation (8.3.6) is true.

8.3.2The input resistance of a CE amplifier can be

increased at the expense of reduced voltage and

current gains by leaving a portion of the emitter

resistance unbypassed. Consider the CE amplifier

shown in Figure P8.3.2 having an unbypassed

emitter resistanceRE 1. Assuming for simplicity

thatro →∞, draw the ac equivalent circuit

for small signals and discuss the effects on input

resistance and voltage and current gains.