8/9/2019 Final Exam 1435-1436 Term 1

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8/9/2019 Final Exam 1435-1436 Term 1

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Question 3 Field-Effect Transistors (40 minutes) 

a.  [2 marks] Explain the difference between the depletion and enhancement FET, and the difference

 between the JFET and the MOSFET.

 b.  [2 marks] Sketch the transfer characteristics describing the gate-to-source voltage and the

saturation drain-to-source current relationship in n-channel enhancement MOSFETs.

c.  [6 marks] The n-channel enhancement MOSFET shown in Fig. 1 is designed to have the

following parameters: = 100 µ ⁄ , ⁄ = 32,  and = 0.7 . Assume that the

values of the DC voltage sources are: Vaa = 2.5 , and Vdd = 5 , and that = 3   and

= 0.4 . Compute the value of the resistances Rd and RS.

d.  Assume that the n-channel enhancement MOSFET in part (c) connected in the amplifier circuit

shown in Fig. 2, where = 310 kΩ, = 90 kΩ, = 820 Ω, = 22 F, and = 100 .

i.  [6 marks] Determine the DC gate-to-source voltage, drain-to-source current, and drain-to-

source voltage of the MOSFET. What is the region of operation of the MOSFET?ii.  [8 marks] Determine the small-signal input resistance, output resistance, voltage gain and

low-frequency cut-off of the amplifier circuit.

Question 4 Bipolar Junction Transistors (40 minutes)

a.  [2 marks] Sketch the transfer characteristics describing the collector-to-emitter voltage and the

collector current relationship for various values of constant base current in npn BJTs.

 b. 

[8 marks] The npn BJT shown in Fig. 3 is designed to have = 100 and = 100 . Assumethat = 1 Ω, and = 100 Ω. Determine the DC collector current, base current, and

collector-to-emitter voltage of the BJT. What is the region of operation of the BJT?

c.  Assume that the npn BJT in part (b) is connected in the amplifier circuit shown in Fig. 4, and that

= 31 kΩ, = 9 kΩ, = 820 Ω, = 2.2 Ω,, and = 22 F.

i.  [6 marks] Determine the DC collector current, base current, and collector-to-emitter

voltage of the BJT. What is the region of operation of the BJT?

iii.  [8 marks] Determine the small-signal input resistance, output resistance, voltage gain and

low-frequency cut-off of the amplifier circuit.

Question 5 Operational Amplifiers (15 minutes)

a.  [4 marks] For the circuit shown in Fig. 5.a, find the transfer function ⁄ . What is the transfer

function if the resistance  is replaced by a capacitor ?

 b. 

[4 marks] For the circuit shown in Fig. 5.b, derive and expression of  as a function of and .

What is the condition for the circuit to function as a difference amplifier?