# Microwave Engineering Questions and Answers – PIN Diodes

This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “PIN Diodes”.

1. A PIN diode consists of ______number of semiconductor layers.
a) Three
b) Two
c) Four
d) One

Explanation: PIN diode is a p-type, intrinsic, n-type diode consisting of narrow layer of p-type semiconductor and a narrow layer of n-type semiconductor material, with a thicker region of intrinsic or very lightly n doped semiconductor sandwiched between them.

2. The material out of which PIN diode is made is:
a) Silicon
b) Germanium
c) GaAs
d) None of the mentioned

Explanation: Silicon is the semiconductor normally used because of its power handling capability and it offers high resistivity for the intrinsic region. But depending on the application, these days GaAs is also used in fabricating PIN diodes.

3. The behavior of a PIN diode is entirely different from normal diodes at all frequency of operation.
a) True
b) False

Explanation: PIN diode acts as a ordinary diode at frequencies up to about 100MHz. at high frequencies it stops to rectify and then acts as a variable resistance.

4. The junction resistance and capacitance of the intrinsic region in a PIN diode are connected______ in the equivalent circuit of PIN diode.
a) Series
b) Parallel
c) Connected across package capacitance
d) None of the mentioned

Explanation: The junction capacitance Cj and junction resistance Rj of a PIN diode are connected in parallel in the equivalent circuit of a PIN diode. The package resistance and package capacitance are connected in series to these junction parameters.

5. The resistance of the PIN diode with positive bias voltage:
a) Increases
b) Decreases
c) Remains constant
d) Insufficient data

Explanation: When the bias is varied on the PIN diode, its microwave resistance RJ changes from a typical value of 6 KΩ under negative bias to perhaps 5 Ω under forward bias. Thus if the diode is mounted on a 50Ω coaxial line, it will not significantly load this line.
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6. A PIN diode can be used in either a series or a shunt configuration to form a __________
a) Single pole single throw switch
b) Single pole double throw switch
c) Amplifier
d) Oscillator

Explanation: A PIN diode can be used in either a series or a shunt configuration to form a single pole single throw switch. In the series configuration, the switch is on when the diode is forward biased and off when the diode is reverse biased.

7. The working principle of series and shunt configuration single pole single throw switch is the same.
a) True
b) False

Explanation: In the series configuration, the switch is on when the diode is forward biased and off when the diode is reverse biased. In the shunt configuration, forward biasing the diode cuts-off the transmission while reverse biasing the diode ensures transmission from input to output.

8. Under ideal conditions, when a PIN diode is used as a switch, the switch must have _______ insertion loss in the ON state.
a) Maximum
b) Zero
c) Average
d) Insertion loss cannot be defined for a switch

Explanation: Ideally, when PIN diode is used as switch, the switch should have zero insertion loss in the ON state and infinite attenuation in the OFF state. These are ideal conditions. But practically a good operating switch must have low insertion loss.

9. When PIN diode is used as a switch, the expression for insertion loss of the switch is given by:
a) 10 log (Po/PL)
b) 10 log (PL/P0)
c) 10 log (PL. Pₒ)
d) None of the mentioned

Explanation: Insertion loss of a switch is defined as the ratio of incident power applied to the load when switch is absent to the actual power delivered to the load.

10. For a shunt configuration switch, the diode impedance is 40 Ω and the terminated line characteristic impedance is 50 Ω. Then the insertion loss of the switch is:
a) 2.2 dB
b) 4.2 dB
c) 8.4 dB
d) 3.6 dB

Explanation: Insertion loss of a shunt configuration switch is given by 20 log (2ZD+Z0/2ZD). Substituting the given values in the above expression, the insertion loss of the shunt configuration switch is 4.2 dB.

11. In the series configuration of a PIN diode switch, the terminated load impedance was found to be 50 Ω and the diode impedance was 60 Ω. Then the insertion loss of the switch is:
a) 4 dB
b) 2 dB
c) 3.6 dB
d) 4.8 dB

Explanation: Insertion loss of a shunt configuration switch is given by 20 log (2ZD+Z0/2ZD). Substituting the given values in the above equation, the insertion loss is 4 dB.

12. The number of PIN diodes used in SPST switch and SPDT switch are the same.
a) True
b) False

Explanation: The number of PIN diodes in SPST switch is one, while the number of PIN diodes used in single pole double throw switch is two.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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