Electronic Devices and Circuit Theory

Robert Boylestad, Louis Nashelsky

Chapter 8

FET Amplifiers - all with Video Answers

Educators

Chapter Questions

Problem 1

Calculate $g_{m 0}$ for a JFET having device parameters $I_{D S S}=12 \mathrm{~mA}$ and $V_{P}=-4 \mathrm{~V}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 2

Determine the pinch-off voltage of a JFET with $g_{m 0}=10 \mathrm{mS}$ and $I_{D S S}=12 \mathrm{~mA}$.

Anand Jangid

Numerade Educator

Problem 3

For a JFET having device parameters $g_{m 0}=5 \mathrm{mS}$ and $V_{P}=-4 \mathrm{~V}$, what is the device current at $V_{G S}=0 \mathrm{~V} ?$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 4

Calculate the value of $g_{m}$ for a JFET $\left(I_{D S S}=12 \mathrm{~mA}, V_{P}=-3 \mathrm{~V}\right)$ at a bias point of $V_{G S}=$ $-0.5 \mathrm{~V}$

Amit Srivastava

Amit Srivastava

Numerade Educator

Problem 5

For a JFET having $g_{m}=6 \mathrm{mS}$ at $V_{G S_{0}}=-1 \mathrm{~V}$, what is the value of $I_{D S S}$ if $V_{P}=-2.5 \mathrm{~V}$ ?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 6

A JFET $\left(I_{D S S}=10 \mathrm{~mA}, V_{P}=-5 \mathrm{~V}\right)$ is biased at $I_{D}=I_{D S S} / 4$. What is the value of $g_{m}$ at that bias point?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 7

Determine the value of $g_{m}$ for a JFET $\left(I_{D S S}=8 \mathrm{~mA}, V_{P}=-5 \mathrm{~V}\right)$ when biased at $V_{G S_{Q}}=V_{P} / 4$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 8

A specification sheet provides the following data (at a listed drain-source current):
$$
g_{f s}=4.5 \mathrm{mS}, \quad g_{o s}=25 \mu \mathrm{S}
$$
At the listed drain-source current, determine:
a. $g_{m}$
1

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 9

For a JFET having specified values of $g_{f_{s}}=4.5 \mathrm{mS}$ and $g_{\sigma s}=25 \mu \mathrm{S}$, determine the device output impedance $Z_{o}(\mathrm{FET})$ and device ideal voltage gain $A_{5}(\mathrm{FET})$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 10

If a JFET having a specified value of $r_{d}=100 \mathrm{k} \Omega$ has an ideal voltage gain of $A_{v}(\mathrm{FET})=-200$, what is the value of $g_{m}$ ?

Varsha Aggarwal

Varsha Aggarwal

Numerade Educator

Problem 11

Using the transfer characteristic of Fig. $69:$
a. What is the value of $g_{m} 0$ ?
b. Determine $g_{m}$ at $V_{G S}=-0.5 \mathrm{~V}$ graphically.
c. What is the value of $g_{m}$ at $V_{G S_{0}}=-0.5 \mathrm{~V}$ using Eq. $(6) ?$ Compare with the solution to part
(b).
d. Graphically determine $g_{m}$ at $V_{G S}=-1 \mathrm{~V}$.
e. What is the value of $g_{m}$ at $V_{G S_{0}}=-1 \mathrm{~V}$ using Eq. (6)? Compare with the solution to part
(d).

AB

Aqib Basheer

Numerade Educator

Problem 12

Using the drain characteristic of Fig. 70 :
a. What is the value of $r_{d}$ for $V_{G S}=0 \mathrm{~V}$ ?
b. What is the value of $g_{m 0}$ at $V_{D S}=10 \mathrm{~V}$ ?

Chai Santi

Numerade Educator

Problem 13

For a 2N4220 $n$ -channel JFET $\left[g_{f}\right.$ (minimum) $=750 \mu \mathrm{S}, g_{a s}$ (maximum) $=10 \mu \mathrm{S}$ :
a. What is the value of $g_{m}$ ?
b. What is the value of $r_{d}$ ?

Chai Santi

Numerade Educator

Problem 14

a. Plot $g_{m}$ versus $V_{G S}$ for an $n$ -channel JFET with $I_{D S S}=12 \mathrm{~mA}$ and $V_{P}=-6 \mathrm{~V}$.
b. Plot $g_{m}$ versus $I_{D}$ for the same $n$ -channel JFET as part (a).

Chai Santi

Numerade Educator

Problem 15

Sketch the ac equivalent model for a JFET if $g_{f s}=5.6 \mathrm{mS}$ and $g_{a s}=15 \mu \mathrm{S}$.

Chai Santi

Numerade Educator

Problem 16

Sketch the ac equivalent model for a JFET if $I_{D S S}=10 \mathrm{~mA}, V_{P}=-4 \mathrm{~V}, V_{G S_{Q}}=-2 \mathrm{~V}$, and $g_{o s}=25 \mu \mathrm{S} .$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 17

Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. 71 if $I_{D S S}=10 \mathrm{~mA}, V_{P}=-6 \mathrm{~V}$, and $r_{d}=40 \mathrm{k} \Omega$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 18

a. Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. 71 if $I_{D S s}$ and $V_{P}$ are one-half the values of Problems 17 . This is $I_{D S S}=5 \mathrm{~mA}$ and $V_{P}=-3 \mathrm{~V}$.
b. Compare the solutions to that of Problem 17 .

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 19

a. Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. 72 if $I_{\mathrm{DSS}}=10 \mathrm{~mA}, V_{P}=-4 \mathrm{~V}$, and $r_{d}=20 \mathrm{k} \Omega$
b. Repeat part (a) with $r_{d}=40 \mathrm{k} \Omega$. What was the impact on the results?

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 20

Determine $Z_{i}, Z_{o}$ and $A_{v}$ for the network of Fig. 73 if $g_{f}=3000 \mu \mathrm{S}$ and $g_{\text {os }}=50 \mu \mathrm{s}$.

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 21

Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. 75 if the $20-\mu \mathrm{F}$ capacitor is removed and the parameters of the network are the same as in Problem $20 .$ Compare results with those of Problem $20 .$

Narayan Hari

Numerade Educator

Problem 22

Repeat Problem 20 if $g_{o s}$ is $10 \mu \mathrm{S}$. Compare the results to those of Problem 20 .

James Kiss

Numerade Educator

Problem 23

a. Find the value of $R_{S}$ to obtain a voltage gain of 2 for the network of Fig. 74 using $r_{d}=\infty \Omega$.
b. Repeat part (a) with $r_{d}=30 \mathrm{k} \Omega$. What was the impact of the change in $r_{d}$ on the gain and the analysis?

Kajal Gautam

Numerade Educator

Problem 24

Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. 75 if $I_{D S S}=6 \mathrm{~mA}, V_{P}=-6 \mathrm{~V}$, and $g_{o s}=40 \mu \mathrm{S} .$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 25

Determine $Z_{i}, Z_{o}$, and $V_{o}$ for the network of Fig. 76 if $V_{i}=20 \mathrm{mV}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 26

Repeat Problem 25 with the capacitor $C_{S}$ removed and compare results.

Narayan Hari

Numerade Educator

Problem 27

Repeat Problem 25 if $r_{d}=20 \mathrm{k} \Omega$ and compare results.

Kajal Gautam

Numerade Educator

Problem 28

Repeat Problem 26 if $r_{d}=20 \mathrm{k} \Omega$ and compare results.

Kajal Gautam

Numerade Educator

Problem 29

Determine $Z_{i}, Z_{m}$ and $V_{n}$ for the network of Fig. 77 if $V_{i}=4 \mathrm{mV}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 30

Repeat Problem 29 if $r_{d}=20 \mathrm{k} \Omega$ and compare results.

Kajal Gautam

Numerade Educator

Problem 31

Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. 78 if $r_{d}=30 \mathrm{k} \Omega$.

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 32

Determine $Z_{i}, Z_{m}$, and $A_{v}$ for the network of Fig. $79 .$

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 33

Repeat Problem 32 if $r_{d}=20 \mathrm{k} \Omega$ and compare results.

Kajal Gautam

Numerade Educator

Problem 34

Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. $80 .$

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 35

Determine $V_{o}$ for the network of Fig. 81 if $g_{o s}=20 \mu \mathrm{S}$.

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 36

Determine $Z_{i}, Z_{o}$ and $A_{v}$ for the network of Fig. 82 if $r_{d}=60 \mathrm{k} \Omega$.

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 37

Repeat Problem 36 if $r_{d}=25 \mathrm{k} \Omega$ and compare results.

Kajal Gautam

Numerade Educator

Problem 38

Determine $V_{o}$ for the network of Fig. 83 if $V_{i}=1.8 \mathrm{mV}$.

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 39

Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the network of Fig. 84 .

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 40

Determine $g_{m}$ for a MOSFET if $V_{G S(T h)}=3 V$ and it is biased at $V_{G S_{0}}=8 \mathrm{~V}$. Assume $k=0.3 \times 10^{-3}$

Chai Santi

Numerade Educator

Problem 41

Determine $Z_{i}, Z_{o}$, and $A_{v}$ for the amplifier of Fig. 85 if $k=0.3 \times 10^{-3}$.

Prachita Kush

Numerade Educator

Problem 42

Repeat Problem 41 if $k$ drops to $0.2 \times 10^{-3}$. Compare results.

Raj Bala

Numerade Educator

Problem 43

Determine $V_{o}$ for the network of Fig. 86 if $V_{i}=20 \mathrm{mV}$.

Thomas Thompson

Thomas Thompson

Numerade Educator

Problem 44

Determine $V_{o}$ for the network of Fig. 86 if $V_{i}=4 \mathrm{mV}, V_{G S(\mathrm{Th})}=4 \mathrm{~V}$, and $I_{D(\mathrm{on})}=4 \mathrm{~mA}$, with $V_{G S(\mathrm{an})}=7 \mathrm{~V}$ and $g_{o s}=20 \mu \mathrm{S}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 45

Determine the output voltage for the network of Fig. 87 if $V_{i}=0.8 \mathrm{mV}$ and $r_{d}=40 \mathrm{k} \Omega$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 46

Design the fixed-bias network of Fig. 88 to have a gain of 8 .

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 47

Design the self-bias network of Fig. 89 to have a gain of $10 .$ The device should be biased at $V_{G S_{Q}}=\frac{1}{3} V_{P}$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 48

For the self-bias JFET network of Fig. 90 :
a. Determine $A_{v_{\mathrm{N}},}, Z_{i}$, and $Z_{D}$.
b. Sketch the two-port model of Fig. 75 of the chapter "BJT AC Analysis" with the parameters determined in part (a) in place.
c. Determine $A_{v_{L}}$ and $A_{v_{v}}$
d. Change $R_{\text {sig }}$ to $10 \mathrm{k} \Omega$ and calculate the new levels of $A_{v_{L}}$ and $A_{v_{i}}$. How is the voltage gain affected by an increase in $R_{s}$ ?
e. For the change of part (d), determine $Z_{i}$ and $Z_{o}$. What was the effect on both impedances?

Prachita Kush

Numerade Educator

Problem 49

For the source-follower network of Fig. $91:$
a. Determine $A_{v_{N}}, Z_{i}$, and $Z_{b}$
b. Sketch the two-port model of Fig. 75 of the chapter "BJT AC Analysis" with the parameters determined in part (a) in place.
c. Determine $A_{v_{L}}$ and $A_{y_{j}}$
d. Change $R_{L}$ to $4.7 \mathrm{k} \Omega$ and calculate $A_{v_{L}}$ and $A_{v_{x}}$. What was the effect of increasing levels of $R_{L}$ on both voltage gains?
e. Change $R_{\text {sig }}$ to $20 \mathrm{k} \Omega$ (with $R_{L}$ at $2.2 \mathrm{k} \Omega$ ) and calculate $A_{\mathrm{v}}$ and $A_{v_{-}}$. What was the effect of increasing levels of $R_{\text {sig }}$ on both voltage gains?
f. Change $R_{L}$ to $4.7 \mathrm{k} \Omega$ and $R_{\mathrm{sig}}$ to $20 \mathrm{k} \Omega$ and calculate $Z_{i}$ and $Z_{o} .$ What was the effect on both impedance parameters?

Prachita Kush

Numerade Educator

Problem 50

For the common-gate configuration of Fig. 92:
a. Determine $A_{v_{\mathrm{N}}}, Z_{i}$, and $Z_{o}$.
b. Sketch the two-port model of Fig. 75 of the chapter "BJT AC Analysis" with the parameters determined in part (a) in place.
c. Determine $A_{v_{L}}$ and $A_{v_{j}}$
d. Change $R_{L}$ to $2.2 \mathrm{k} \Omega$ and calculate $A_{v_{L}}$ and $A_{v_{x}} .$ What was the effect of changing $R_{L}$ on the voltage gains?

Prachita Kush

Numerade Educator

Problem 51

For the JFET cascade amplifier in Fig. 93 , calculate the de bias conditions for the two identical stages, using JFETs with $I_{D S S}=8 \mathrm{~mA}$ and $V_{P}=-4.5 \mathrm{~V}$.

Dominador Tan

Numerade Educator

Problem 52

For the JFET cascade amplifier of Fig. 93, using identical JFETs with $I_{D S S}=8 \mathrm{~mA}$ and $V_{P}=-4.5 \mathrm{~V}$, calculate the voltage gain of each stage, the overall gain of the amplifier, and the output voltage $V_{o}$

Dominador Tan

Numerade Educator

Problem 53

If both JFETs in the cascade amplifier of Fig. 93 are changed to those having specifications $I_{D S S}=12 \mathrm{~mA}$ and $V_{P}=-3 \mathrm{~V}$, calculate the resulting dc bias of each stage.

Dominador Tan

Numerade Educator

Problem 54

If both JFETs in the cascade amplifier of Fig. 93 are changed to those having the specifications $I_{D S S}=12 \mathrm{~mA}, V_{P}=-3 \mathrm{~V}$, and $g_{o s}=25 \mu \mathrm{S}$, calculate the resulting voltage gain for each stage, the overall voltage gain, and the output voltage, $V_{o}$.

Dominador Tan

Numerade Educator

Problem 55

For the cascade amplifier of Fig. 93, using JFETs with specifications $I_{D S S}=12 \mathrm{~mA}$, $V_{P}=-3 \mathrm{~V}$, and $g_{a s}=25 \mu \mathrm{S}$, calculate the circuit input impedance $\left(Z_{i}\right)$ and output impedance $\left(Z_{\circ}\right)$.

Dominador Tan

Numerade Educator

Problem 56

For the cascade amplifier of Fig. 94, calculate the de bias voltages currents of each stage.

Dominador Tan

Numerade Educator

Problem 57

For the amplifier circuit of Fig. 94, calculate the voltage gain of each stage and the overall amplifier voltage gain.

Dominador Tan

Numerade Educator

Problem 58

Calculate the input impedance $\left(Z_{i}\right)$ and output impedance $\left(Z_{o}\right)$ for the amplifier circuit of Fig. 94 .

Arpit Gupta

Numerade Educator

Problem 59

Using PSpice Windows, determine the voltage gain for the network of Fig. 73 .

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 60

Using Multisim, determine the voltage gain for the network of Fig. 75 .

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 61

Using PSpice Windows, determine the voltage gain for the network of Fig. 76 .

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 62

Using Multisim, determine the voltage gain for the network of Fig. 77 .

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 63

Using PSpice Windows, determine the voltage gain for the network of Fig. $82 .$

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 64

Using PSpice Windows, determine the voltage gain for the network of Fig. 85 .

Khoobchandra Agrawal

Khoobchandra Agrawal

Numerade Educator

Problem 65

Use the Design Center to draw a schematic circuit of the cascade JFET amplifier as in Fig. $93 .$ Set the JFET parameters for $I_{D S S}=12 \mathrm{~mA}$ and $V_{P}=3 \mathrm{~V}$, and have the analysis determine the de bias.

Dominador Tan

Numerade Educator

Problem 66

Use the Design Center to draw a schematic circuit for a cascade JFET amplifier as shown in Fig. 93. Set the analysis to calculate the ac output voltage $V_{o}$ for $I_{D S S}=12 \mathrm{~mA}$ and $V_{P}=-3 \mathrm{~V}$

Dominador Tan

Numerade Educator