Anna University - Electronic Device and Circuits (EDC) - April / May 2011 - Two Marks with Answers

B.E./B.TECH. DEGREE EXAMINATION, - APRIL/MAY 2011

Electrical and Electronics Engineering (EEÈ) - Third Semester

ELECTRONIC DEVICES AND CIRCUTS

April / May 2011 - Solved Electronic Device and Circuits Two Marks

1.What is hole and electron in a pn-diode?

An electron is negatively charged. The electrons in the outer shell determine the electrical characteristics of each particular type of atom.
A hole is defined as an absence of an electron in a shell where one could exists.

2.Draw a series voltage regulator circuit with an error amplifier.

3.What is the early effect in CB configuration and give its consequences?

An increase in magnitude of collector voltage increases the space charge width at the output junction. Due to this the effective base width (w) decreases and this phenomenon is known as early effect.

Consequences

The charge gradient is increased within the base and consequently the current due to minority charge carriers injected across the emitter junction increases.

4. Why we use h-parameters to describe a transistor?

h-parameters (hybrid) are real numbers at audio frequencies, are easy to measure, can also be obtained from the transistor static characteristic curves and are convenient to use in circuit analysis and design.

h-parameters are used to obtain transistor linear model.

5. Write the expression for ON resistance in JFET?

where L = length of channel(m)
e = magnitude of electronic charge (c)
W = channel dimension (m)
NDµn= number o donor atoms (electrons/m3)

6. Define pinch-off voltage and give expression?

The ohmic relationship between VDS (drain to source voltage) and ID (Drain current) continues till VDS reaches a certain critical value called pinch-off voltage (Vp) when ID becomes constant at its maximum value called IDSS

where

e = 1.6 x10-19 c
ε = dielectric constant of channel material;

ND = no. of donor atoms (electrons/cm3)

7.State Barkhausen criterion?

It states that:

• The magnitude of product of open loop gain of the amplifier (A) and the magnitude of feedback factor (β) is unity (|Aβ|=1)
• The total phase shift around a loop, as signal proceeds from input through amplifier, feedback network back to input again, completing a loop is 0° or 360°.

8.Define frequency stability in oscillator?

The measure of ability of an oscillator to maintain the desired frequency as precisely as possible for as long a time as possible is called as frequency stability of an oscillator.

9.Draw differentiator and integrator circuit?

10. For astable multivibrator with c1 = c2 = 1000 pF and R1 = R2 = 20 kΩ calculate frequency of oscillation.

Anna University - Electronic Device and Circuits (EDC) - May / June 2010 - Solved Two Marks

B.E/B.Tech Degree Examination, May/June 2010

• 3rd Semester EEE

Electronics Devices and Circuits

(2008 Regulations)

 Two Marks with Answers for May / June 2010 Question Paper:

1. Define diffusion current.

There may exist an additional current due to the transport of charge in a semiconductor. Such an additional current is due o the phenomenon called diffusion. The current due to the diffusion is called diffusion current.

2. What are the applications of LED?

* All kinds of displays,
* in the optical devices such as opto coupler.
* As on-off indicator
* In remote controls andapplication like burglar alarm.

3. What is the relation IE ,IC ,and IB in CB configuration?

IE=IC+IB

IE=IC                      IC=IB

(since IB is negligible in CB) 

4. Why are power transistor provided with heat sinks?

A thermal heat sink is usually used to draw heat from the device via thermal conductor which expels the heat into the ambient air via thermal cdnvection and heat radiation.

5. What is MOSFET? What are the types of MOSFET?

MOSFET: Metal oxide semiconductor field effect transistor It is a second category of field effect transistor.
Types:
* Depletion MOSFET (D-MOSFET) * Enhancement MOSFET (E-MQSFET)

6.Compare JFET and BJT:

7.Write the essential conditions for maintaining oscillations?

The two essential conditions for maintaining oscillations are called Barkhausen creiterion. .
1.The total phase shift around loop must be 0 degree or 360 degree.

2. The product of open loop gain(β) and feedback factor (β) i.e |Aβ| = 1

8.What do you understand by feed back in amplifier?

A small portion of output is fed back to input is called feedback.
When I/P and part of O/P in phase the feedback is positive feedback. When it is in out of phas, is called negative feedback.

9. Draw a simple integrating circuit.



10. What is called as clipper circuits?

The circuits which are used to clip off unwanted portion of the waveform, without disturbing the remaining part of the waveform are called clipper circuits or clippers.