Match List - I with List - II. Choose the correct answer from the options given below :List - I (Microwave devices) List - II (Name of device) (A) Microwave transistor (I) CCD (B) Field effect transistor (II) InP diodes (C) Transferred electron device (III) Read diode (D) Avalanche transit time device (IV) HBT
(A)-(IV), (B)-(I), (C)-(II), (D)-(III)
Two of the pairings are definitional and settle the code: (A)-(IV), (B)-(I), (C)-(II), (D)-(III), option 1.
(C) Transferred electron device and InP. A transferred-electron device is the Gunn diode, and it works only in materials whose conduction band has a low-mass central valley and higher-lying satellite valleys. At a high enough field, electrons are transferred from the light valley to the heavy one, where their mobility is far lower — so the drift velocity falls as the field rises:
\(\dfrac{dv}{dE}\lt0\)
That negative differential mobility makes domains of space charge form and travel, producing oscillation at the transit frequency \(f=v/L\). Only a few materials have the required band structure, and GaAs and InP are the two used — silicon cannot do it at all.
(D) Avalanche transit time device and the Read diode. The IMPATT family exploits two delays that together give a 180° phase shift between voltage and current: the avalanche build-up lags the field by 90°, and the transit of the generated carriers across a drift region adds another 90°. The result is negative resistance at microwave frequencies. W. T. Read proposed the original n+-p-i-p+ structure in 1958, and the Read diode is its name.
(A) Microwave transistor and HBT. A heterojunction bipolar transistor uses a wide-gap emitter, which blocks hole back-injection from base to emitter and so keeps the injection efficiency high even with a heavily doped base. Heavy base doping means low base resistance and a very thin base, so both the transit time and the RC delay fall — which is what makes the HBT the standard microwave bipolar device.
(B) Field effect transistor and CCD. The remaining pairing, taken by elimination. Both are surface field-effect structures on a MOS foundation: a CCD is a chain of MOS gates in which the surface potential well is controlled by the gate voltage, exactly as in a field-effect transistor.
The quickest route : InP can only belong to the transferred-electron entry, since that is the material class the effect requires, and "Read diode" can only be the avalanche transit-time device. Those two alone leave option 1.
Hence, the correct code is (A)-(IV), (B)-(I), (C)-(II), (D)-(III).
Similar Questions
There are three general purpose microwave tubes. The first is ordinary gridded tube, having electrodes like vacuum tube diode and triodes. The second type are those in which interaction between the electron beam and RF field takes place. The klystron is the example of the second type of microwave tubes. The third category of the device is one in which interaction between an RF field and electron beam is continuous. TWT (Travelling Wave Tube) is the example of this category.
Read the paragraph and answer the questions :
Microwave tubes are used as microwave amplifiers and oscillators. Three general type of microwave tubes in which third type tubes are important because in these tubes there is an interaction between an electron and an RF field is continuous. The Travelling Wave Tube (TWT) is the prime example of this interaction. It is an amplifier, whose oscillator counter part is called Backward Wave Oscillator (BWO). The second sub-group consists of tubes in which a magnetic field ensures a constant electron beam – RF field interaction, and this is complemented by the Cross-Field Amplifier (CFA). Multicavity Klystron is used as high and very high power amplifiers in the UHF and microwave ranges. The frequency range covered is from about 250 MHz to over 95 GHz. The reflex-Klystron is a low power microwave oscillator. It is assumed that oscillations are started by switching transients. For oscillations to be maintained the transient time in the repeller space cycle is given as \(T=\left(n+\dfrac{3}{4}\right)\) where n is an integer, each value of n is said to correspond to different reflex klystron mode. Reflex Klystrons with integral cavities are available in the frequency range 4 to 200 GHz.
The correct sequence of sub-systems of Klystron amplifiers as they appear in the direction of flow of electron beam is
Assertion (A) : TWTA is a narrow band device and has a helical structure and it is used as amplifier and oscillator.
Reason (R) : In TWT, the electron beam travels through a slow-wave structure and speed of electron beam is \(\dfrac{1}{10}\) of the velocity of light.
The primary function of the helix in a travelling wave tube is to
The Multicavity Klystron
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Indicate the false statement. Klystron amplifiers may use intermediate cavities to
One of the following is unlikely to be used as a pulsed device. It is the
In a two cavity Klystron the secondary cavity is called
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