Monday, December 8, 2014

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 k. Calculate the high frequency cutoff (upper 3dB frequency) of the amplifier. Given gm = 2 mA/V, Cgd = 2 pF, Cds = 2 pF, rd = 100 k and Cgs = 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, rd = 10 k, Cgs = 5 pF, Cgd = 1 pF and Cds = 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 M 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


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 rd = 10 kΩ is used in a common source configuration as shown. The JFET capaciances are Cgs = 5 pF, Cgd = 2 pF and Cds = 2 pF. 
Determine the ac small signal mid band voltage gain (Vo/Vs) 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 Av = Vo/Vi of the JFET amplifier shown in the figure is IDSS = 10 mA, VP = 5 volts. Assume C1, C2 and Cs 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 rd = 20 K, IDSS = 10 mA, VP = - 8 volts.

 11.   Zi and Zo 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.   ID and VDS 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





2013

3.       The small signal resistance (ie. dVB/dID) in K offered by the n – channel MOSFET M shown in the figure below, at a bias point of VB = 2 volts is (device data for M: device Transconductance parameter KN = µNCOX(W/L) = 40 µA/V2, threshold voltage VTN = 1 volt, and neglecting body effect and channel length modulation effects)
a.       12.5
b.      25
c.       50
d.      100
Answer:   B


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


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