PCBWay

Q.1. What is integrated circuit (IC)?

Answer: Integrated circuit means that all the components in each circuit are fabricated on the same chip.

Q.2. What are linear ICs?

Answer: A linear integrated circuit is a solid state analog device characterized by a theoretically infinite number of possible operating states. It operates over a continuous range of input levels. Within a certain input range, the amplification curve of a linear IC is a straight line i.e. the input and output voltages are directly proportional. The best known and most common linear IC is the operational amplifier or op amp.

Q.3. What is an operational amplifier?

Answer: An operational amplifier is a directly coupled high gain amplifier consisting of one or more differential amplifiers, usually followed by a level translator and an output stage. The output stage is generally a push pull amplifier. It can be used to amplify DC as well as AC input signals.

Q.4. What is the use of level translators?

Answer: Because of direct coupling, dc level at the emitters rises from stage to stage. This increase dc level tends to shift the operating point of the succeeding stage and therefore limits the output voltage swing a may even distort the output signal. So to increase this dc level, level translator circuits are used.

Q.5. What is differential amplifier and its significance?

Answer: A differential amplifier is an amplifier which is used to amplify the difference between the two input signals. It suppresses the unwanted disturbances that might be amplified with the desired signal.

Q.6. What are the important features of differential amplifier?

Answer: The important features of differential amplifier are-

  • High differential gain and low common mode gain.
  • High common mode rejection ratio (CMRR).
  • High input impedance. Low output impedance.
  • High gain. Large bandwidth.

Q.7. How differential amplifiers can be configured and what are they?

Answer: A differential amplifier consists of two transistors. Depending on the way of connecting the input to them and depending on the way of measuring output, there are four configurations of differential amplifier, they are:

  • Dual input balanced output differential amplifier.
  • Dual input unbalanced output differential amplifier.
  • Single input balanced output differential amplifier.
  • Single input unbalanced output differential amplifier.

Q.8. What is common mode rejection ratio (CMRR)?

Answer: Common mode rejection ratio is the ability of a differential amplifier to reject the common mode signals successfully. It is called as a figure of merit of a differential amplifier. Ideally, the CMRR should be infinite and practically it should be as high as possible.

Q.9. How CMRR can be improved?

Answer: CMRR is the ratio of differential voltage gain (Ad) to the common mode voltage gain (Ac), so we can improve the CMRR by either increasing differential voltage gain or by decreasing common mode voltage gain.

To increase CMRR, emitter resistance RE should be increased. Higher the value of RE , more is the negative feedback and less is the common mode gain. Thus with the increase in RE , common mode voltage gain decreases and CMRR increases.

Q.10. What is the drawback of op amp IC 741?

Answer: The drawback of IC 741 is its low slew rate (0.5v/µs), which limits its use in relatively high frequency applications, especially in oscillators, comparators and filters.

Q.11. What is current mirror?

Answer: A current mirror is a circuit designed to copy a current through one active device by controlling the current in another device of a circuit, keeping the output current constant regardless of loading.

Q.12. What  is the advantage of using a current mirror circuit?

Answer: The advantage of using current mirror circuit is that it requires less number of components than the constant current bias circuit. It is simple and easy to fabricate. Therefore the current mirror circuit is widely used in the integrated amplifiers.

Q.13. What is the advantage of using a constant current bias circuit?

Answer: Constant current bias circuit supplies constant emitter current. It also provides very high source resistance since the AC equivalent of the DC current source is ideally an open circuit.

Q.14. How ICs are classified?

Answer: ICs are classified according to the number of components or gates in the case of digital ICs integrated on the same chip as follows:

  • Small scale integration (SSI) < 10 components.
  • Medium scale integration (MSI) < 100 components.
  • Large scale integration (LSI) > 100 components.
  • Very large scale integration (VSSI) > 1000 components.

Q.15. What are the important characteristics of an ideal op amp?

Answer: The important characteristics of an ideal op amp are as follows-

  • Infinite open loop voltage gain.
  • Infinite input resistance.
  • Zero output resistance.
  • Zero offset voltage.
  • Infinite bandwidth.
  • Infinite CMRR.
  • Infinite slew rate.
  • Zero power supply rejection ratio.

Q.16. Define slew rate.

Answer: Slew rate is defined as the maximum rate of change of output per unit time and it is expressed in volts/microsecond.

Q.17. What is the importance of slew rate?

Answer: Slew rate decides the capability of op amp to change its output rapidly; hence it decides the highest frequency of operation of a given op-amp.

Q.18. What are the features of IC 741?

Answer: The features of IC 741 are-

  • No frequency compensation required.
  • Short circuit protection.
  • Offset voltage null capability.
  • Large common mode and differential voltage ranges.
  • No latch ups.

Q.19. Why op-amp is not used as an amplifier in the open loop configuration?

Answer: In practice the open loop op-amp is not used due to the following reasons-

  • Due to very large open loop gain, distortion is introduced in the amplified output signal.
  • The open loop gain does not remain constant. It varies with changes in temperature and power supply.
  • The bandwidth of an op-amp in the open loop mode is very small almost zero. For this reason the open loop op-amp is not used in practice as an amplifier.
  • However the op-amp in open loop configuration is used in applications such as comparators (both inverting and non inverting comparators).

Q.20. What are the advantages of negative feedback?

Answer: Negative feedback is used in the amplifier circuits as they provide the following improvements in the operation of an amplifier-

  • It reduces and stabilizes the gain.
  • Reduces the distortion.
  • Increases the bandwidth.
  • Changes the value of input and output resistances.
  • Reduces the effect of variations in temperature and supply voltage on the output of the op-amp.

Q.21. What is the difference between positive feedback and negative feedback?

Answer: If the feedback signal and the original input signal are in phase with each other then it is called as the positive feedback.

If the signal feedback to the input and the original input signal are 180∘out of phase, then it is called as the negative feedback.

Q.22. What is the virtual short or virtual ground concept?

Answer: According to the virtual short concept, the potential difference between the two input terminals of an op-amp is almost zero. In other words both the input terminals are approximately at the same potential.

Q.23. What is input offset voltage?

Answer: Input offset voltage is the voltage that must be applied between the two input terminals of an op-amp to null the output.

Q.24. What is input offset current?

Answer: The algebraic difference between the currents into the inverting and non inverting terminals is referred to as input offset current.

Q.25. What is input bias current?

Answer: Input bias current is the average of the currents that flow into the inverting and non inverting terminals of the op-amp.

Q.26. What are the features of a voltage follower circuit and what is its application?

Answer: The important features of the voltage follower circuit are as follows-

  • Closed loop voltage gain is equal to 1, i.e output is equal to input with no phase shift.
  • Very high input impedance.
  • Very low output impedance.
  • Large bandwidth.

Application- Voltage followers are placed between two networks to reduce the loading on the first network. This is due to the high input impedance offered by the voltage follower.

Q.27. What are op-amp characteristics and its significance?

Answer: Op-amp characteristics are classified into two categories namely dc characteristics and ac characteristics. DC characteristics includes-

  • Input bias current.
  • Input offset current.
  • Input offset voltage.
  • Thermal drift.

Ac characteristics includes-

  • Frequency response.
  • Stability. Frequency compensation.
  • Slew rate.

The op-amp characteristics are important in practice because we can use them to compare the performance of various op-amp ICs and select the best suitable from them for the required application.

Q.28. What is the output resistance of op-amp IC 741?

Answer: Output resistance is the equivalent resistance that can be measured between the output terminal of the op-amp and ground. It is 75 ohm or IC 741.

Q.29. What is input capacitance of op-amp?

Answer: Input capacitance is the equivalent capacitance, measured at either the inverting or non inverting terminal with the other terminal connected to ground.

Q.30. What is power supply rejection ratio (PSRR)?

Answer: The change in an op-amp input offset voltage caused by the variation in the supply voltage is called as power supply rejection ratio (PSRR).

Q.31. What is gain bandwidth (GB) product?

Answer: The gain bandwidth product is the bandwidth of the op-amp when the voltage gain is 1.

Q.32. What are the parameters that should be considered for AC applications?

Answer: The parameters that should be considered for AC applications are-

  • Input and output resistance.
  • Output voltage swing.
  • Slew rate.
  • Gain bandwidth product.
  • Input offset voltage and current.
  • Equivalent noise voltage and current.

Q.33. What are the parameters that should be considered for DC applications?

Answer: The parameters that should be considered for DC applications are-

  • Input and output resistance.
  • Output voltage swing.
  • Input offset voltage and current.
  • Large signal voltage gain.

Q.34. Define frequency response of an op-amp.

Answer: The frequency response of an op-amp is the graph of its open loop gain versus frequency. The open loop gain is generally expressed in dB and frequency is plotted on the logarithmic scale. Ideally the open loop gain of the op-amp is expected to remain constant irrespective of frequency. That means ideally the bandwidth of op-amp should be infinite but practically it is not so.

Q.35. What is transient response?

Answer: It is that portion of the complete response before attaining some fixed value at the output.

Q.36. What is steady state response?

Answer: The response of the network after it attains a fixed value is called as steady state response.

Q.37. Define full power bandwidth.

Answer: It is defined as the maximum frequency at which the op-amp will yield an undistorted ac output with the largest possible signal amplitude. The amplitude is dependent on the type of op-amp and the power supplies.

Q.38. What is unity gain bandwidth (UGB)?

Answer: The frequency at which the gain equals one is known as the unity gain bandwidth. For an op-amp with a single break frequency, the gain bandwidth (GB) product is constant and equal to unity gain bandwidth (UGB).

Q.39. What is the corner or break frequency?

Answer: It is the frequency at which gain A is 3 dB down from its value at 0 Hz.

Q.40. Define bandwidth of an amplifier.

Answer: Bandwidth of an amplifier is the range or band of frequencies for which the gain remains constant.

Q.41. What is the difference between inverting and non inverting amplifier?

Answer: Inverting amplifier is an amplifier in which the signal which is to amplified is applied at the inverting (-) terminal of the op-amp. The amplified output signal will be 180∘out of phase with the input signal. In other words the output signal is inverted.

Non inverting amplifier is an amplifier in which the signal which is to be amplified is applied to the Non inverting (+) terminal of the op-amp. The input and output voltages are in phase with each other.

Q.42. Which type of feedback is used in Non inverting amplifier?

Answer: Voltage series feedback is used in Non inverting amplifier.

Q.43. Which type of feedback is used in inverting amplifier?

Answer: Voltage shunt feedback is used in inverting amplifier.

Q.44. What is Instrumentation amplifier?

Answer: An instrumentation amplifier is basically a difference amplifier which must satisfy the following requirements-

  • Precise low level signal amplification.
  • Low noise. Low thermal drift.
  • High input resistance.
  • Low power dissipation.
  • High CMRR.
  • High slew rate.

This amplifier amplifies the low level output signal of the transducer to such a level that it can drive the indicator or display.

Q.45. What is transducer?

Answer: Transducer is a device which is used to convert one from of energy into another.

Q.46. What will be the output of an integrator if sine wave is applied at the input?

Answer: The output of the integrator is a cosine wave when the input is a sine wave.

Q.47. What are the applications of an Integrator?

Answer: Some of the important applications of an integrator are- In the triangular wave or ramp generators. In the analog to digital converters. In the integral type controllers used in a closed loop control system. In analog computers to solve differential equations.

Q.48. What will be the output of a differentiator for a square wave input?

Answer: The output voltage is in the form of a spikes corresponding to the rising and falling edges of the square wave and the output voltage is zero when the input is constant.

Q.49. What will be the output of a differentiator for a sine wave input?

Answer: The output voltage will be an inverse cosine wave.

Q.50. What are the applications of a differentiator?

Answer: The applications of a differentiator are- In the PID controllers. As a high pass filter. In the wave shaping circuits to generate narrow pulses corresponding to any sharp change in the input signal.