Previous GATE Questions on Analysis and Frequency Response of FET Amplifiers (1987 - Till Date)

1993

8.       A JFET with the following parameters is used in a single stage common source amplifier with a load resistance of 100 kΩ. Calculate the high frequency cutoff (upper 3dB frequency) of the amplifier. Given g_m = 2 mA/V, C_gd = 2 pF, C_ds = 2 pF, r_d = 100 kΩ and C_gs = 1 pF.

Answer:   6.67 MHz               
  Solution:  https://www.youtube.com/watch?v=pwhijWtJvLY

1994

13.   In the MOSFET amplifier shown in the figure below, the transistor has µ = 50, r_d = 10 kΩ, C_gs = 5 pF, C_gd = 1 pF and C_ds = 2 pF.

Draw a small signal equivalent circuit for the amplifier for mid band calculate its mid band voltage gain.

Answer:    -7.04
                Solution:   https://www.youtube.com/watch?v=fMOdjBi0tHI

1995

16.   In the JFET circuit shown, assume that R₁//R₂ = 1 MΩ and the total stray capacitance at the output to be 20 pF.

        Determine the upper cutoff frequency of the amplifier.

Answer:    3.18 MHz
                Solution:  https://www.youtube.com/watch?v=joc09FhNQI8

1998

4.       From a measurement of the rise time of the output pulse of an amplifier, whose input is a small amplitude square wave, one can estimate the following parameter of the amplifier

            a.       Gain-bandwidth product

            b.      Slew rate

            c.       Upper 3 dB frequency

            d.      Lower 3 dB frequency

Answer:   C

Solution :  https://www.youtube.com/watch?v=1-COkXWLdJ0

13.   In the MOSFET amplifier of the figure, the signal output V₁ and V₂ obey the relationship

Answer:   D

Solution :    https://www.youtube.com/watch?v=dHIC1z_RdEY

1999

28.   A JFET having µ = 50 and r_d = 10 kΩ is used in a common source configuration as shown. The JFET capaciances are C_gs = 5 pF, C_gd = 2 pF and C_ds = 2 pF. 

Determine the ac small signal mid band voltage gain (V_o/V_s) and the upper 3 dB frequency of the circuit.

Answer:    -25, 4 MHz
                       Solution:  https://www.youtube.com/watch?v=Uzt9ZG6ctvE

2002

6.       The voltage gain A_v = V_o/V_i of the JFET amplifier shown in the figure is I_DSS = 10 mA, V_P = 5 volts. Assume C₁, C₂ and C_s to be very large.

a.       + 16

b.      – 16

c.       + 8

d.      – 6

Answer:   D

                   Solution:   https://www.youtube.com/watch?v=9K_U1BcpZSI

2005

Common Data Questions for 11, 12 and 13:

Given r_d = 20 KΩ, I_DSS = 10 mA, V_P = - 8 volts.

 11.   Z_i and Z_o of the circuit are respectively

a.       2 MΩ and 2 KΩ

b.      2 MΩ and 20/11 KΩ

c.       Infinity and 2 KΩ

d.      Infinity and 20/11 KΩ

Answer:   B

12.   I_D and V_DS under DC conditions are respectively

a.       5.625 mA and 8.75 Volts

b.      7.50 mA and 5.0 Volts

c.       4.50 mA and 11.0 Volts

d.      6.25 mA and 7.5 Volts

Answer:   A

13.   Transconductance in milli-siemens (mS) and the voltage gain of the amplifier are

a.       1.875 mS and  3.41

b.      1.875 mS and – 3.41

c.       3.30 mS and – 6

d.      3.30 mS and  6

Answer:   B

Solution:  https://www.youtube.com/watch?v=3EaSdIyGqME

2013

3.       The small signal resistance (ie. dV_B/dI_D) in KΩ offered by the n – channel MOSFET M shown in the figure below, at a bias point of V_B = 2 volts is (device data for M: device Transconductance parameter K_N = µ_NC_OX(W/L) = 40 µA/V², threshold voltage V_TN = 1 volt, and neglecting body effect and channel length modulation effects)

a.       12.5

b.      25

c.       50

d.      100

Answer:   B

Solution:  https://www.youtube.com/watch?v=78GP87ThDTg

4.       The ac schematic of an NMOS common source stage is shown in the figure below, where part of the biasing circuit has been omitted for simplicity. For the n – channel MOSFET M, the Transconductance gm = 1 mA/V and body effect and channel length modulation effect are to be neglected. The lower cutoff frequency in Hz of the circuit approximately at

a.       8

b.      32

c.       50

d.      200

Answer:   A

Solution:  https://www.youtube.com/watch?v=2-LoL607LVE