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.