Summer 2017 – Q.3

3. (a) Define Op-Amp. Draw and explain the functional block diagram of an Op-Amp. [6M]

i) It is a high grain DC amplifier with high input impedance and low output impedance.
ii) It is very sensitive electronic device. It does mathematical as well as logical operation that is why it is known as operational amplifier.
iii) It is a voltage controlled voltage source (VCVS) device.
iv) For op-amp, we generally use on IC 741 which has max. power supply of ±15V.

Functional block diagram

Input differential amplifier:- It is dual input balanced output differential amplifier which provides major part of high gain and high input impedance. If input is AC then output is also AC.

Intermediate differential amplifier:- It is dual input unbalanced output differential amplifier. Which is also used for increasing the gain of amplifier. Since It is direct coupled amplifier, so DC voltage at the output of intermediate stage may arise.

Level shifter:- It is emitter follower, main function of level shifter is to eliminate DC present at the output of intermediate stage. If has high value of input impedance and low value of output impedance.

Complimentary push pull amplifier:- It is a class B power amplifier. In general used at the final stage. Since it is the power amplifier, so it can drive high value of load.

(b) Write law of commutation, law of association and law of distribution for AND and OR logic function. [6M]

Commutative law:-
Law 1:- A+B = B+A
This law states that A OR B is the same as B OR A

Law 2:- $latex A\cdot B=B\cdot A$
This law states that A and B is same as that of B and A.

Law of association:-
Law 1:- (A+B)+C = A+(B+C)
A OR B ORed with C is same as A ORed with B OR C.

Law 2:- $latex \left(A\cdot B\right)\cdot C=A\cdot\left(B\cdot C\right)$
A AND B ANDed with C is same as A ANDed with B AND C.

Distributive laws:-
Law 1:- $latex A\left(B+C\right)=A\cdot B+A\cdot C$
States that ORing of several variables and ANDing the result with a single variable is equivalent to ANDing that single variable with each of the several variable and then ORing the producers.

Law 2:- A+BC = (A+B) (A+C)
This law states that ANDing of several variables and ORing the result with a single variable is equivalent to ORing that single variable with each of the several variable and then ANDing the sums.