Important Short Questions and Answers: Characteristics of op-amp

Characteristics of Op-Amp

1.What are the advantages of ICs over discrete circuits.?

1.        Minimization & hence increased equipment density.

2.        Cost reduction due to batch processing.

3.        Increased system reliability

4.        Improved functional performance.

5.        Matched devices.

6.        Increased operating speeds

7.        Reduction in power consumption

2.   What is OPAMP?

An operational amplifier is a direct coupled high gain amplifier consisting of one or more differential amplifiers , followed by a level translator and an output stage.It is a versatile device that can be used to amplify ac as well as dc input signals & designed for computing mathamatical functions such as addition, subtraction , multiplication, integration & differentiation

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3.Draw the pin configuration of IC741.

4. List out the ideal characteristics of  OPAMP?

( i )Open loop gain infinite

(ii)Input impedance infinite

(iii)Output impedance low

(iv)Bandwidth infinite

(v)Zero offset,ie, V_o=0 when V₁=V₂=0

5.what are the different kinds of packages of IC741? a)Metal

a) can (TO) package

b) Dual- in- line package

c)Flat package or flat pack

6.What are theassumptions made from ideal opamp characteristics?

i)The current drawn by either of the input terminals(non-inverting/inverting) is negligible.

ii)the potential difference between the inverting & non- inverting input terminals is zero.

7. Mention some of the linear applications of op – amps :

Adder, subtractor, voltage –to- current converter, current –to- voltage converters, instrumentation amplifier, analog computation ,power amplifier, etc are some of the linear op-amp circuits.

8.Mention some of the non – linear applications of op-amps:-

Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti –log amplifier, multiplier are some of the non – linear op-amp circuits.

9.What are the areas of application of non- linear op- amp circuits?

¯          industrial instrumentation

¯          Communication

¯          Signal processing

10.What happens when the common terminal of V⁺ and V^- sources is not grounded?

If the common point of the two supplies is not grounded, twice the supply voltage will get applied and it may damage the op-amp.

11.Define input offset voltage.

A small voltage applied to the input terminals to make the output voltage as zero when the two input terminals are grounded is called input offset voltage.

12. Define input offset current. State the reasons for the offset currents at the input of the op-amp.

The difference between the bias currents at the input terminals of the op-amp is called as input offset current. The input terminals conduct a small value of dc current to bias the input transistors.Since the input transistors cannot be made identical,there exists a difference in bias currents.

13. Define CMRR of an op-amp.

The relative sensitivity of an op-amp to a difference signal as compared to a common –mode signal is called the common –mode rejection ratio. It is expressed in decibels.

CMRR= Ad/Ac

14.In practical op-amps, what is the effect of high frequency on its performance?

The open- loop gain of op-amp decreases at higher frequencies due to the presence of parasitic capacitance. The closed- loop gain increases at higher frequencies and leads to instability.

15. What is the need for frequency compensation in practical op-amps?

Frequency compensation is needed when large bandwidth and lower closed loop gain is desired. Compensating networks are used to control the phase shift and hence to improve the stability.

16.Mention the frequency compensation methods.

*Dominant-pole compensation

*Pole- zero compensation.

17.What are the merits and demerits of Dominant-pole compensation? *noise immunity of the system is improved.

*Open-loop bandwidth is reduced.

18.Define slew rate.

The slew rate is defined as the maximum rate of change of output voltage caused by a step input voltage.An ideal slew rate is infinite which means that op-amp’s output voltage should change instantaneously in response to input step voltage.

19.Why IC 741 is not used for high frequency applications?

IC741 has a low slew rate because of the predominance of capacitance present in the circuit at higher frequencies. As frequency increases the output gets distorted due to limited slew rate.

20.What causes slew rate?

There is a capacitor with- in or outside of an op-amp to prevent oscillation.It is this capacitor which prevents the output voltage from responding immediately to a fast changing input.

21.Define thermal drift.

The bias current , offset current & offset voltage change with temperature. A circuit carefully nulled at 25^oC may not remain so when the temperature raises to 35^oC.This is called thermal drift . Often, offset current drift is expressed in nA/ ^o C and offset voltage drift in mV/ ^oC.

22.Define supply voltage rejection ratio(SVRR)

The change in OPAMP’s input offset voltage due to variations in supply voltage is called the supply voltage rejection ratio.It is also called Power Supply Rejection Ratio(PSRR) or Power Supply Sensitivity(PSS).