Microwave Engineering Multiple Choice Questions on “Applications of RF Diodes”.
1. Classical p-n junction diode cannot be used for high frequency applications because of:
A. High bias voltage
B. High junction capacitance
C. Frequency sensitive
D. High forward biased current
Answer: B
Clarification: p-n junction diodes have high junction capacitance that makes them not suitable for high frequency applications. A Schottky barrier diode relies on a semiconductor metal junction and hence making them suitable for high frequency application.
2. Schottky barrier diode is a sophisticated version of the point contact ______________
A. Germanium diode
B. Silicon crystal diode
C. GaAs diode
D. None of the mentioned
Answer: B
Clarification: Schottky barrier diode is a sophisticated version of the point contact silicon crystal diode, wherein the metal-semiconductor junction so formed is a surface rather than a point contact as it is in point contact silicon crystal diode.
3. Advantage of Schottky diode over silicon crystal diode is the presence minority charge carriers.
A. True
B. False
Answer: B
Clarification: The advantage of Schottky diode over point contact silicon crystal diode is the elimination of minority carrier flow in the reverse biased condition of the diode. Due to the elimination of holes, there is no delay due to hole-electron recombination and hence operation is faster.
4. As the area of rectifying contact goes on increasing, the forward resistance of the Schottky diode:
A. Increases
B. Decreases
C. Remains unchanged
D. None of the mentioned
Answer: B
Clarification: The noise and forward resistance of Schottky diode is small as compared to the noise figure and forward resistance of point contact silicon crystal diode. Hence, as the area of rectifying contact goes on increasing, the forward resistance decreases.
5. The number of semiconductor layers in a TRAPATT diode is:
A. Two
B. Three
C. Four
D. One
Answer: B
Clarification: Silicon is usually used for the manufacture of TRAPATT diodes and they have a configuration p+ nn+ the p-N junction is reverse biased beyond the breakdown region, so that the current density is larger.
6. In order to achieve high current density, a compromise in _______is made in a TRAPATT diode.
A. Gain
B. Size
C. Operating frequency
D. No compromise is made on any of the parameter
Answer: C
Clarification: When a high current density achieved, it decreases the electric field in the space charge region and increases the carrier transit time. Due to this, the frequency of operation gets lowered to less than 10 GHz. But efficiency is increased due to low power dissipation.
7. TRAPATT diode is normally mounted at a point inside a coaxial resonator where there is minimum RF voltage swing.
A. True
B. False
Answer: B
Clarification: Inside a coaxial resonator, the TRAPATT diode is normally mounted at a point where maximum RF voltage swing is obtained. When the combined DC bias and RF voltage exceeds breakdown voltage, avalanche occurs and a plasma of holes and electrons are generated which get trapped.
8. A major disadvantage of TRAPATT diode is:
A. Fabrication is costly
B. Low operational bandwidth
C. Low gain
D. High noise figure
Answer: D
Clarification: The disadvantages of TRAPATT diode are high noise figure and generation of strong harmonics due to the short duration of the current pulse. Since short duration of current pulses are used, they find application in S band pulse transmitters.
9. _________ gives a frequency domain representation of a signal, displaying the average power density versus frequency.
A. CRO
B. Oscilloscope
C. Spectrum analyzer
D. Network analyzer
Answer: C
Clarification: Spectrum analyzer gives a frequency domain representation of a signal, displaying the average power density versus frequency. Thus, its function is dual to that of oscilloscope, which displays the time domain representation of a signal.
10. The most important functional unit of a spectrum analyzer is:
A. Mixer
B. IF amplifier
C. Sensitive receiver
D. None of the mentioned
Answer: C
Clarification: A spectrum analyzer basically consists of a sensitive receiver that tunes over a specified frequency band and gives out a video output that is proportional to the signal power in a narrow bandwidth.
11. A tunnel diode is a p-n junction diode with a doping profile that allows electron tunneling through a narrow energy band gap.
A. True
B. False
Answer: A
Clarification: A tunnel diode is a pn junction diode with a doping profile that allows electron tunneling through a narrow energy band gap leading to negative resistance at high frequencies. Tunnel diode can be used for both oscillators and amplifiers.
Microwave Engineering,