Instrumentation Systems : Chapter 4: OPAMP as Signal Conditioner

 Q. Draw symbol of operational amplifier.

Answer: 

Q. Draw the block diagram of operational amplifier and explain each block.

Answer: 

Input stage: It provides most of the voltage gain of OP-AMP and decides value of input resistance.

Intermediate stage: This is usually another differential amplifier but with single output.

Level Shifting Stage: It receives an amplified signal with some non-zero dc level.

It brings dc level to zero volts.

Output stage: It increases voltage and current supplying capability of OP-AMP. It also decreases output resistance.

Q. Give ideal characteristics of operational amplifier.

Answer: The ideal characterisics of operational amplifier are:

1. Voltage gain is infinite.

2. Input resistance is infinite.

3. Output resistance is zero.

4. Offset voltage is zero. (zero voltage when off).

5. Bandwidth is infinite.

6. PSSR=0. Power supply rejection ratio.

Q. Define the following parameters of OP-AMP.

1. CMRR:

Answer: It is defined as the ratio of differential gain to common mode gain.

2.PSRR:

Answer: The change in op-amp input offset voltage due to variation in supply voltage is called as power supply rejection ratio.

3. Slew Rate:

Answer: It is the maximum rate of change of output voltage per unit time.

4. Output offset voltage:

Answer: The output voltage produced due to input offset voltage is called as output offset voltage.

5. Input bias current:

Answer: It is the average of currents flowing into the two input terminals of op-amp.

Q. Define the term 'feedback' and state its type.

Answer: It is defined as the process in which a part of output signal is returned back to the input.

It is of two types : 

1. Positive feedback: If the feedback signal and the original input signal are in phase with each other it is called positive feedback.

2. Negative feedback: If the feedback signal and original signal are 180 degree out of phase, then it is negative feedback.

Q. Explain concept of virutal ground in op-amp.

Answer: 

Concept of virtual ground:

1. If non-inverting terminal of OP-AMP is connected to ground then inverting terminal will also be at ground potential.

2. Hence it is said to be virtual ground.

2. Similarly, if inverting terminal of OP-AMP is connected to ground then non-inverting terminal will be at virtual ground potential.