Field Effect Transistor Amplifiers - MCQs

Multiple Choice Questions Topic Outline

• MCQs in FET Amplifiers
• MCQs in FET Small-Signal Model
• MCQs in JFET Fixed-Bias Configuration
• MCQs in JFET Self-Bias Configuration
• MCQs in JFET Voltage-Divider Configuration
• MCQs in JFET Source-Follower (Common-Drain) Configuration
• MCQs in JFET Common-Gate Configuration
• MCQs in Depletion-type MOSFETs
• MCQs in Enhancement-type MOSFETs
• MCQs in E-MOSFET Drain-Feedback Configuration
• MCQs in E-MOSFET Voltage-Divider Configuration
• MCQs in Designing FET Amplifier Networks

Begin and Good luck!

1. FET amplifiers provide ________.

• A) excellent voltage gain
• B) high input impedance
• C) low power consumption
• D) All of the above

2. A BJT is a ________-controlled device.

• A) current
• B) voltage
• C) power
• D) resistance

3. An FET is a ________-controlled device.

• A) current
• B) voltage
• C) power
• D) resistance

4. The E-MOSFET is quite popular in ________ applications.

• A) digital circuitry
• B) high-frequency
• C) buffering
• D) All of the above

5. What is the range of g_m for JFETs?

• A) 1 µS to 10 µS
• B) 100 µS to 1000 µS
• C) 1000 µS to 5000 µS
• D) 10000 µS to 100000 µS

6. For what value of I_D is g_m equal to 0.5 g_m0?

• A) 0 mA
• B) 0.25 I_DSS
• C) 0.5 I_DSS
• D) I_DSS

7. What is the typical value for the input impedance Z_i for JFETs?

• A) 100 kΩ
• B) 1 MΩ
• C) 10 MΩ
• D) 1000 MΩ

8. Referring to the transfer characteristics shown below, calculate g_m at V_GSQ = –1 V.

• A) 2 mS
• B) 3 mS
• C) 4 mS
• D) 5 mS

9. Use the following equation to calculate gm for a JFET having I_DSS = 10 mA, V_P = –5 V, and V_GSQ = –2.5 V.

• A) 2 mS
• B) 3 mS
• C) 4 mS
• D) 5 mS

10. Referring to the following figure, calculate g_m for V_GSQ = –1.25 V.

• A) 2 mS
• B) 2.5 mS
• C) 2.75 mS
• D) 3.25 mS

11. Referring to this figure, obtain g_m for I_D = 6 mA.

• A) 2.83 mS
• B) 3.00 mS
• C) 3.25 mS
• D) 3.46 mS

12. Referring to the figure below, determine the output impedance for V_GS = –3 V at V_DS = 5 V.

• A) 100 kΩ
• B) 80 kΩ
• C) 25 kΩ
• D) 5 kΩ

13. Calculate g_m and r_d if y_fs = 4 mS and y_os = 15 ΩS.

• A) 4 mS, 66.7 kΩ
• B) 4 mS, 15 kΩ
• C) 66.7 kΩ, 4 mS
• D) None of the above

14. The steeper the slope of the I_D versus V_GS curve, the ________ the level of g_m.

• A) less
• B) same
• C) greater

15. When V_GS = 0.5 V_p g_m is ________ the maximum value.

• A) one-fourth
• B) one-half
• C) three-fourths
• D) two-thirds

16. If I_D = I_DSS / 2, g_m = ___________ g_mo.

• A) 1
• B) 0.707
• C) 0.5
• D) 1.414

17. The more horizontal the characteristic curves on the drain characteristics, the ________ the output impedance.

• A) less
• B) same
• C) greater

18. What is (are) the function(s) of the coupling capacitors C₁ and C₂ in an FET circuit?

• A) to create an open circuit for dc analysis
• B) to isolate the dc biasing arrangement from the applied signal and load
• C) to create a short-circuit equivalent for ac analysis
• D) All of the above

19. Where do you get the level of g_m and r_d for an FET transistor?

• A) from the dc biasing arrangement
• B) from the specification sheet
• C) from the characteristics
• D) All of the above

20. Referring to this figure, find Z_o if y_os = 20 µS.

• A) 1.85 kΩ
• B) 1.92 kΩ
• C) 2.05 kΩ
• D) 2.15 kΩ

21. Referring to this figure, calculate A_v if y_os = 20 µS.

• A) –3.48
• B) –3.56
• C) –3.62
• D) –4.02

22. For the fixed-bias configuration, if r_d < 10 • R_D, then Z_o = ________.

• A) R_D
• B) R_D || r_d
• C) RG
• D) -gm • (R_D || r_d)

23. Which of the following is a required condition to simplify the equations for Z_o and A_v for the self-bias configuration?

• A) r_d ≤ 10R_D
• B) r_d = R_D
• C) r_d ≥ 10R_D
• D) None of the above

24. Referring to this figure, calculate Z_o if y_os = 40 µS.

• A) 2.92 kΩ
• B) 3.20 kΩ
• C) 3.25 kΩ
• D) 3.75 kΩ

25. On which of the following parameters does r_d have no or little impact in a source-follower configuration?

• A) Zi
• B) Zo
• C) Av
• D) All of the above

26. Referring to this figure, calculate Z_o for V_GSQ = –3.2 V.

• A) 362.52 Ω
• B) 340.5 Ω
• C) 420.5 Ω
• D) 480.9 Ω

27. Referring to this figure, calculate Z_i for y_os = 20 µS. Assume V_GSQ = −2.2V.

• A) 300.2 Ω
• B) 330.4 Ω
• C) 340.5 Ω
• D) 350.0 Ω

28. Which of the following is (are) related to depletion-type MOSFETs?

• A) V_GSQ can be negative, zero, or positive.
• B) g_m can be greater or smaller than g_m0’.
• C) I_D can be larger than I_DSS’.
• D) All of the above

29. Referring to this figure, calculate A_v for y_os = 58 µS.

• A) –7.29
• B) –7.50
• C) –8.05
• D) –8.55

30. Referring to this figure, calculate Z_i if r_d = 19 kΩ.

• A) 2.42 MΩ
• B) 2.50 MΩ
• C) 2.53 MΩ
• C) 2.59 MΩ

31. Referring to this figure, calculate Z_o if r_d = 19 kΩ.

• A) 1.75 kΩ
• B) 1.81 kΩ
• C) 1.92 kΩ
• D) 2.00 kΩ

32. Referring to this figure, calculate A_v if r_d = 19 kΩ.

• A) –2.85
• B) –3.26
• C) –2.95
• D) –3.21

33. Determine the value for R_D if the ac gain is 8.

• A) 1.51 kΩ
• B) 1.65 kΩ
• C) 1.85 kΩ
• D) 2.08 kΩ

34. Referring to this figure, calculate the value of R_D if the ac gain is 10. Assume V_GSQ = ¼V_p.

• A) 2.2 kΩ
• B) 2.42 kΩ
• C) 2.62 kΩ
• D) 2.82 kΩ

35. For an FET small-signal amplifier, one could go about troubleshooting a circuit by ________.

• A) viewing the circuit board for poor solder joints
• B) using a dc meter
• C) applying a test ac signal
• D) All of the above

Fill-in-the-blanks Questions

1. A field-effect transistor amplifier provides excellent voltage gain with the added feature of a _____ input impedance.

• A) low
• B) medium
• C) high
• D) None of the above

2. The depletion MOSFET circuit has a _____ input impedance than a similar JFET configuration.

• A) much higher
• B) much lower
• C) lower
• D) higher

3. The _____ is quite popular in digital circuits, especially in CMOS circuits that require very low power consumption.

• A) JFET
• B) BJT
• C) D-type MOSFET
• D) E-type MOSFET

4. _____ is the amplification factor in FET transistor amplifiers.

• A) Z_i
• B) g_m
• C) I_D
• D) I_G

5. _____ is an undefined quantity in a JFET.

• A) A_i
• B) A_v
• C) Z_i
• D) Z_o

6. The _____ controls the _____ of an FET.

• A) I_D’, V_GS
• B) V_GS’, I_D
• C) I_G’, V_DS
• D) I_G’, I_D

7. Transconductance is the ratio of changes in _____.

• A) I_D to V_GS
• B) I_D to V_DS
• C) V_GS to I_G
• D) V_GS to V_DS

8. The transconductance g_m _____ as the Q-point moves from V_p to I_DSS

• A) decreases
• B) remains the same
• C) increases
• D) None of the above

9. g_m has its maximum value for a JFET at _____.

• A) V_p
• B) 0.5 V_p
• C) 0.3 V_p
• D) I_DSS

10. The value of gm is at its maximum g_m0 at VG_S equal to _____ and zero at V_GS equal to _____.

• A) 0 V, V_p
• B) V_p, 0 V
• C) 0.5V_p, 0.3V_p
• D) 0.3V_p , 0.5V_p

11. The range of input impedance Z_i for MOSFETs is _____.

• A) 1 kΩ –10 kΩ
• B) 100 kΩ –1 MΩ
• C) 10 MΩ –100 MΩ
• D) 10¹² Ω to 10¹⁵ Ω

12. The range of output admittance y_os for FETs is _____.

• A) 5 µS –10 µS
• B) 10 µS –50 µS
• C) 50 µS –100 µS
• D) 200 µS –500 µS

13. The _____ configuration has the distinct disadvantage of requiring two dc voltage sources.

• A) self-bias
• B) voltage-divider
• C) fixed-bias
• D) All of the above

14. _____ is the network-input impedance for a JFET fixed-bias configuration.

• A) R_G
• B) R_D
• C) Zero
• D) None of the above

15. _____ is a required step in order to calculate Z_o.

• A) Setting I_G equal to zero
• B) Setting V_i equal to zero
• C) Setting I_D equal to I_DSS
• D) None of the above

16. _____ configuration(s) has (have) Z_o ≈ R_D.

• A) Fixed-bias
• B) Self-bias
• C) Voltage-divider
• D) All of the above

17. _____ is the only parameter that is different between voltage-divider and fixed-bias configurations.

• A) Z_i
• B) A_v
• C) Z_o
• D) None of the above

18. The input and output signals are in phase in a _____ configuration.

• A) fixed-bias
• B) source-follower
• C) voltage-divider
• D) self-bias

19. A _____ configuration has a voltage gain less than 1.

• A) fixed-bias
• B) self-bias
• C) source-follower
• D) voltage-divider

20. The input and output signals are 180º out of phase in a _____ configuration.

• A) source-follower
• B) common-gate
• C) common-drain
• D) voltage-divider

21. The isolation between input and output circuits in the ac equivalent circuit is lost in a _____ configuration.

• A) common-gate
• B) common-source
• C) common-drain
• D) None of the above

22. The _____ configuration has an input impedance, which is other than R_G.

• A) common-source
• B) common-gate
• C) common-drain
• D) None of the above

23. The gate-to-source voltage V_GS of a(n) _____ must be larger than the threshold V_GS(Th) for the transistor to conduct.

• A) JFET
• B) D-type MOSFET
• C) E-type MOSFET
• D) None of the above

24. r_d changes from one operation region to another with _____ values typically occurring at _____ levels of V_GS (closer to zero).

• A) lower, lower
• B) lower, higher
• C) higher, lower
• D) None of the above

25. The _____ does not support Shockley's equation.

• A) JFET
• B) D-type MOSFET
• C) E-type MOSFET
• D) None of the above

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