web 2.0

Site Update

This site will no longer be updated. Please visit ee08.net.tc from now on...

Saturday, December 19, 2009

ANE Lab - Sample Viva

Here is a bunch of questions, thrown by Mr. Ali Mohsin at some of our fellows living in other sections, in a very ridiculous way indeed:

1. Why do we not use collector resistance in common collector configuration? What are its advantages and disadvantages, if any?

Advantage is transistor's protection in case of some-short circuit and disadvantage is increased output impedance (when not bypassed).

2. What's the advantage of using a dual supply?

It makes possible to have zero volt DC level at the output.

3. What is meant by a small signal and a large signal?

A small signal does not affect transistor's parameters (like beta), but a large signal does.

4. Why is common collector known as "emitter-follower"?

Because emitter (output) voltage follows the base (input) voltage.

5. What is the preferred first stage, middle stage(s) and last stage of the multistage amplifier and why?

First stage: Common Source (high input impedance) / Middle stages: Common Emitter (good voltage and current amplification) / Last stage: Common Collector (impedance matching).

6. Tell me the gain in dB, for a multistage amplifier having two stages (or any other number) with individual gains of 100 and 1000 (or any other values)?

Use the formula 20 log (Product of Gains).

7. Draw the AC equivalent circuit of the configuration (CE, CB or CC) which I tell you to draw!

8. Prove to me that in a common collector configuration, the "collector" really is common!

In common collector, collector is at AC ground. Moreover, neither input nor output is taken from it.

9. What is AC load in common emitter amplifier?

R(C) parallel to R(L), as R(E) is bypassed.

10. Why is AC load line steeper than DC load line and what are its effects?

Slope of AC load line is (-1/RC) while that of DC is (-1/RC+RE). It causes clipping and thus lowers the peak-peak voltage.

11. Why is the gain of a common base amplifier lesser at lower frequencies (like 1k)?

Because of low input resistance, according to relation f(c)=1/(2*pi*Rin*C), f(c) is quite high, so gain is lower at lower frequencies.

(So, be prepared for such kinda' questions on your "viva-day". Wishing all of you besta' luck!)


Anonymous said...

hmm nice

Anonymous said...

yar iska answer v likh dete................

Post a Comment