Microwave Engineering Questions and Answers – IMPATT and BARITT Diodes

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

1. The material used to fabricate IMPATT diodes is GaAs since they have the highest efficiency in all aspects.
a) true
b) false
View Answer

Answer: b
Explanation: IMPATT diodes can be fabricated using silicon, germanium, GaAs or indium phosphide. Out of these materials, GaAs have highest efficiency, low noise and high operating frequencies. But GaAs has a major disadvantage of complex fabrication process and higher cost. So, GaAs are not preferred over silicon and germanium.

2. When a reverse bias voltage exceeding the breakdown voltage is applied to an IMPATT diode, it results in:
a) avalanche multiplication
b) break down of depletion region
c) high reverse saturation current
d) none of the mentioned
View Answer

Answer: a
Explanation: A reverse bias voltage exceeding the breakdown voltage is applied to an IMPATT diode, a high electric field appears across the n+ p junction. This high field imparts sufficient energy to the holes and also to valence electrons to raise themselves to the conduction band. This results in avalanche multiplication of electron hole pair.

3. To prevent an IMPATT diode from burning, a constant bias source is used to maintain _______ at safe limit.
a) average current
b) average voltage
c) average bias voltage
d) average resistance
View Answer

Answer: a
Explanation: Avalanche multiplication is a cumulative process resulting in rapid increase of carrier density. To prevent the diode from burning due to this increased carrier density, a constant bias source is used to maintain average current at safe limit.
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4. The number of semiconductor layers in IMPATT diode is:
a) two
b) three
c) four
d) none of the mentioned
View Answer

Answer: c
Explanation: IMPATT diode consists of 4 layers according to the construction. It consists of a p+ region and n+ layers at the two ends. In between these layers, a p type layer and an intrinsic region is sandwiched.

5. The resonant frequency of an IMPATT diode is given by:
a) Vd/2l
b) Vd/l
c) Vd/2πl
d) Vdd/4πl
View Answer

Answer: a
Explanation: The resonant frequency of an IMPATT diode is given by the expression Vd/2l. Here VD is the carrier drift velocity; L is the length of the intrinsic region in the IMPATT diode.

6. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the drift time of the carrier is:
a) 10-11 seconds
b) 2×10-11 seconds
c) 2.5×10-11 seconds
d) none of the mentioned
View Answer

Answer: b
Explanation: The drift time of the carrier is defined as the ratio of length of the intrinsic region to the carrier drift velocity. Substituting the given values in this relation, the drift time of the carrier is 2×10-11 seconds.

7. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the nominal frequency of the diode is:
a) 12 GHz
b) 25 GHz
c) 30 GHz
d) 24 GHz
View Answer

Answer: b
Explanation: Nominal frequency is defined as the ratio of the carrier drift velocity to twice the length of the intrinsic region. Substituting the given values in the above equation, the nominal frequency is 25 GHz.
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8. IMPATT diodes employ impact ionization technique which is a noisy mechanism of generating charge carriers.
a) true
b) false
View Answer

Answer: a
Explanation: IMPATT devices employ impact ionization techniques which is too noisy. Hence in order to achieve low noise figure, impact ionization is avoided in BARITT diodes. The minority injection is provided by punch through of the intermediate region.

9. An essential requirement for the BARITT diode is that the intermediate drift region be completely filled to cause the punch through to occur.
a) true
b) false
View Answer

Answer: b
Explanation: An essential requirement for the BARITT diode is that the intermediate drift region be completely filled to cause the punch through to the emitter-base junction without causing avalanche breakdown of the base collector junction.
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10. If the RMS peak current in an IMPATT diode is 700 mA and if DC input power is 6 watt, with the load resistance being equal to 2.5 Ω, the efficiency of the diode is:
a) 10.1 %
b) 10.21 %
c) 12 %
d) 15.2 %
View Answer

Answer: b
Explanation: Efficiency of IMPATT diode is defined as the ratio of output RMS power to the input DC power. Calculating the RMS output power from the given RMS current and substituting in the equation of efficiency, the efficiency is 10.21%.

11. If the critical field in a Gunn diode oscillator is 3.2 KV/cm and effective length is 20 microns, then the critical voltage is:
a) 3.2 V
b) 6.4 V
c) 2.4 V
d) 6.5 V
View Answer

Answer: b
Explanation: Critical voltage of a Gunn diode oscillator is given by the expression lEc where l is the effective length and Ec is the critical field. Substituting the given values in the above equation, critical voltage is 6.4 volts.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
To practice all areas of Microwave Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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