MICROWAVE SEMICONDUCTOR DEVICES
1) What is Gunn Effect? What are the elements that exhibit Gunn Effect?
Gun effect was first observed by GUNN in n_type GaAs bulk diode. According to GUNN, above some critical voltage corresponding to an electric field of 2000-4000v/cm, the current in every specimen became a fluctuating fuction of time. The frequency of oscillation was determined mainly by the specimen and not by the external circuit.
The elements are
a) Gallium arsenide
b )Indium phosphate
c) Cadmium telluride
2)What are the factors reducing efficiency of IMPATT diode?
1) Space charge effect
2) Reverse saturation current effect
3) High frequency skin effect
4) Ionization saturation effect.
3) What is Transferred electron effect?
Some materials like GaAs exhibit negative differential mobility, when biased above a threshold value of
the electric field. This behavior is called transferred electron effect. The electrons in the lower energy
band will move to the higher energy ban d its called TED.
4) What are the factors reduces the efficiency in Impatt Diode
1)Space charge effect
2)Reverse saturation current effect
3)High frequency skin effect
4)Ionization saturation effect.
5)Mention the ideal characterize of dielectric material in MMIC?
1)Small size and Weight
5)Eventual cost reduction when produced in large quantities.
6)Draw the voltage waveforms of TRAPATT diode
7) What are the necessary condition for Gunn diode
This mode is defined in the region when the fL value is about 107 cm/s and the n0/L > 1012 cm2. In this region the device is unstable because of the cyclic formation of either the accumulation layer or the high field domain.
8)List the advantages of parametric amplifier
ü Positive input impedance
ü More stable
ü Power gain independent of source impendence
ü No circulator required
ü Larger bandwidth
9)What are the two modes available in negative resistance devices?
a) Voltage controlled mode
b) Current controlled mode
10) List the gunn modes of operations.
a) Transit time mode
b) LSA mode
c) Quenched time mode
d) Delayed mode
11) Give the applications of parametric amplifier.
a) space communication systems
b) Radio telescopes and
12) Draw the equivalent circuit for varactor diode
13) Draw the equivalent circuit for Tunnel diode