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08.825: Microwave Devices and Circuits

Question Bank- Module II

Part – A

1. What are the fundamental difference between a transferred electron device and a transistor?

2. What do you mean by Gunn Effect? Explain.

3. Draw the current versus field characteristics of a two valley semiconductor.

4. Explain the LSA mode of operation of a GUNN diode.

5. Explain two valley theory of a semiconductor.

6. Explain hoe a high field domain is formed for microwave generation and amplification.

7. What are the modes of operation of a Gunn diode?

8. For an n-type GaAs Gunn diode following parameters are given:

Electron density n = 1018

cm-3

Electron density at lower valley nl = 1010

cm-3

Electron density at upper valley nu = 108 cm

-3

Temperature T = 300 K

Determine the conductivity of the diode.


Threshold field Eth= 2800V/cm ; applied field E= 3200 V/cm; device length L=10µm; doping

concentration no= 2x1014

cm-3

; operating frequency f= 10GHz.

a. Compute the electron drift velocity.

b. Calculate the current density.

c. Estimate the negative electron mobility.


Electron drift velocity vd= 2.5 x 105 m/s; negative electron mobility |µn| = 0.015m

2/Vs;

relative dielectric constant Ɛr = 13.1. Determine the criterion for classifying the modes of

operation.

11. An LSA oscillator has the following parameters: Conversion efficiency ɳ =0.06;

multiplication factor M=3.5; threshold field Eth= 320k V/m; Device length L= 12µm; donor

concentration no=1021

/cm2; average carrier velocity Vo= 1.5x 10

-5 m/s, determine the output

power in mW.

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12. Explain the working of TRAPATT.

13. Why is TRAPATT diode so called?

14. Explain the working of IMPATT diode.

15. An IMPATT diode has the following parameters:

Carrier drift velocity vd= 2 x 106 cm/s; Drift-region length, L=6µm; Maximum operating

voltage VOmax = 100 V; Maximum operating current UIOmax = 200 mA; efficiency ɳ = 15%;

breakdown voltage V bd = 90V. Compute the maximum CW output power in watts and the

resonant frequency in gigahertz.

16. A TRAPATT diode has the following parameters: doping concentration N A = 2 x 1015

cm-3

;

current density J = 20kA/cm2. Calculate the avalanche-zone velocity.

17. Differentiate between available power gain and transducer power gain.

18.

What do you mean by unconditional stability? State condition for unconditional stability.

19. Explain stability circles.

20. Differentiate between k-Δ test and µ test for unconditional stability.

21. Draw the circuit of a one port negative resistance oscillator.

Part- B

22. Explain the Gunn effect and RWH theory.

23.

Explain the RWH theory for Gunn diode. What are the various Gunn oscillation modes?24. Explain the two valley model theory of Gunn diode. Obtain the condition for negative

resistance.

25. Explain the different modes of operation of a Gunn diode. What is the significance of the

LSA mode of operation?

26. With the help of neat diagram explain the structure and working of IMPATT diode. What is

the maximum possible efficiency of an IMPATT?

27. With the help of neat diagram explain the structure and working of TRAPATT diode. What

is the maximum possible efficiency of a TRAPATT?

28. Explain the steps involved in the design of one port negative resistance oscillator.

29. Explain the steps involved in the design of single stage transistor amplifier.

30. Substantiate that a negative one port oscillator needs cavity for sustained oscillations.

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31. A microwave transistor has the following S parameters at 10GHz, with a 50Ω reference

impedance:

S11 = 0.45

150o

, S12 = 0.01 10o, S21 = 2.45

10o

, S22 = 0.40

150o

The source impedance is Zs =20Ω and the load impedance Zl= 30Ω. Compute the power

gain, the available gain, and the transducer power gain.

32. The S parameter for the HP HFET-102 GaAs FET at 2 GHz with the bias voltage = 0 are

given as follows(Zo=50Ω): S11 = 0.894 150o

, S12 = 3.122 10o

, S21 =0.020 10o

,

S22 = 0.781 150o

. Determine the stability of this transistor by using k-Δ test and µ test for

unconditional stability and plot stability circles on a smith chart.

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