250+ TOP MCQs on MOSFET in Small Signal Operation and Answers

Tricky Electronic Devices and Circuits Questions and Answers on “MOSFET in Small Signal Operation”.

1. An NMOS technology has μ_nC_ox = 50 μA/V² and V_t = 0.7 V. For a transistor with L = 1μm, find the value of W that results in g_m 1mA/V at I_D = 0.5 mA.
A. 10 μm
B. 20 μm
C. 30 μm
D. 40 μm

2. Consider an NMOS transistor having k_n= 2 mA/V². Let the transistor be biased at V_OV = 1V. For operation in saturation, what dc bias current I_D results? If a +0.1-V signal is superimposed on V_GS, find the corresponding increment in collector current by evaluating the total collector current I_D and subtracting the dc bias current I_D.
A. I_D = 1mA and Increment = 0.21 mA
B. I_D = 1mA and Increment = 0.42 mA
C. I_D = 2mA and Increment = 0.21 mA
D. I_D = 2mA and Increment = 0.42 mA

3. We know I_D =1/2 k_n (V_GS + v_gs – V_t)². Let the signal v_gs be a sine wave with amplitude V_gs, and substitute v_gs = V_gs sin ω t in Eq.(5.43). Using the trigonometric identity show that the ratio of the signal at frequency 2ω to that at frequency ω , expressed as a percentage (known as the second-harmonic distortion) is
A. V_gs/V_ov x 100%
B. 1/2V_gs/V_ov x 100%
C. 1/4V_gs/V_ov x 100%
D. 1/8V_gs/V_ov x 100%

4. If in a particular application V_gs is 10 mV, find the minimum overdrive voltage at which the transistor should be operated so that the second-harmonic distortion is kept to less than 1%.
A. 1V
B. 0.75V
C. 0.5V
D. 0.25V

5. If a gain of at least 5 V/V is needed, what value of g_m is required?
A. 0.1 mA/V
B. 0.2 mA/V
C. 0.4 mA/V
D. 0.8 mA/V

Answer: A
Clarification: g_mR_d = 5 or g_m= 5/50 mA/V.

6. Using a dc supply of 3 V, what values of I_D and V_OV would you choose?
A. 0.34 mA and 0.35 V respectively
B. 0.34 mA and 0.69 V respectively
C. 0.034 mA and 0.35 V respectively
D. 0.034 mA and 0.69 V respectively

7. What W/L ratio is required if μ_nC_ox = 200 μA/V²?
A. 1.23
B. 1.23
C. 1.43
D. 1.53

8. Find the small-signal model parameters (g_m, r_o and g_mb) for an NMOS transistor having W/L = 20 μm/2 μm and operating at I_D = 100 μA and |V_SB| = 1V.
A. g_m= 0.42mA/V, r_o= 160 kΩ, g_mb = 0.084 mA/V
B. g_m= 0.21mA/V, r_o= 160 kΩ, g_mb= 0.042 mA/V
C. g_m= 0.42mA/V, r_o= 80 kΩ, g_mb = 0.042 mA/V
D. g_m= 0.24mA/V, r_o= 80 kΩ, g_mb = 0.084 mA/V

9. Find the small-signal model parameters (g_m, r_o and g_mb) for a PMOS transistor having W/L = 20 μm/2 μm and operating at I_D = 100 μA and |V_SB| = 1V.
A. g_m= 0.24mA/V, r_o= 240 kΩ, g_mb = 0.024 mA/V
B. g_m= 0.24mA/V, r_o= 120 kΩ, g_mb = 0.048 mA/V
C. g_m= 0.24mA/V, r_o=240 kΩ, g_mb = 0.048 mA/V
D. g_m= 0.12mA/V, r_o= 240 kΩ, g_mb = 0.048 mA/V

10. The overdrive voltage at which each device must be operating is
A. NMOS = 0.83V and PMOS = 0.48V
B. NMOS = 0.48V and PMOS = 0.83V
C. NMOS = 0.24V and PMOS = 0.41V
D. NMOS = 0.41V and PMOS = 0.24V