linear integrated circuits interview questions

Linear Integrated Circuits Unit 1 : Fundamentals (Short Answers Questions)

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1. What are the advantages of integrated circuits?

  • increased package density.
  • Cost reduction .
  • Increased system reliability.
  • Improved functional performance.
  • Increased operating speeds.
  • Reduction in power consumption.
  • 2. What are the popular IC packages available?

  • Metal can package.
  • Dualinlinepackage.
  • Ceramic flat package.
  • 3. What is an operational amplifier. A variety of mathematical operations can be carried out using operational amplifiers, which are directcoupled high gain amplifiers made up of one or more differential amplifiers.

    4. What is the internal structure of an op-amp and what is a brief description of each block?

    5. What are the characteristics of an ideal op-amp.

  • Open loop voltage gain is infinity.
  • Input impedance is infinity.
  • Output impedance is zero.
  • Bandwidth is infinity.
  • Zero offset.
  • CMRR Infinite.
  • Slew rate Infinite.
  • 6. What are the OP-Amp’s DC and AC characteristics? DC characteristics include input bias current, input offset current, input offset voltage, and thermal drift. AC Characteristics: Slew Rate, Frequency compensation.

    7. Input offset voltage is the voltage imbalance between two op-amp input terminals.

    8. Define input offset current. At the input terminals of the device, the bias currents at each

    9. What is the definition of an opamp’s CMRR? It is the ratio between differential mode gain and common mode gain.

    10. The openloopgain of an op-amp decreases at higher frequencies due to the presence of parasitic capacitance, so what effect does high frequency have on its performance? The closedloopgain increases at higher frequencies and leads to instability.

    11. When large bandwidth and lower closed loop gain are desired, to improve the stability, frequency compensation is required in practical op-amps.

    12. What are the frequency compensation methods?

    13. Define slew rate. The maximum rate of output voltage change resulting from a step input voltage An ideal slew rate is infinite. Units- v/µs.

    14. No, IC 741 cannot be used for high frequency applications due to its slow slew rate.

    15. There is a capacitor inside or outside of an op-amp to prevent oscillation, which is why the slew rate is not infinite in the ideal op-amp.

    16. What are the applications of op-amps?

  • Linear: Adder, subtracter, voltage to current converter, current to voltage converters, instrumentation amplifier, analog computation, power amplifier, Integrator, differentiator etc.
  • Non linear: Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti-logamplifier, multiplier
  • 17. What is an instrumentation amplifier and why is it needed? In many commercial and industrial applications, transducers are typically used to measure physical quantities. For the transducer’s output to power an indicator or display system, it must be amplified. This function isperformed by an instrumentation amplifier.

    18. What are the features of instrumentation amplifier?

  • high gain accuracy
  • high CMRR
  • high gain stability
  • low dc offset
  • low output impedance
  • 19. What are the applications of V-I and I-V converters?

  • V-I:Low voltage dc and ac voltmeter, L E D Tester, Zener diode tester
  • I-V: Digital to Analog converter, Light intensity indicator, photo diode detector
  • 20. What do you mean by a precision diode? Unlike ordinary diodes, which can only rectify voltages up to their cut-off voltage, precision diodes can rectify input signals up to the millivolt range.

    21. What are the applications of precision diode.

  • Half waveRectifier
  • Full Wave rectifier
  • Peak value detector
  • Clipper, Clamper
  • 22. What are the applications of Log amplifier? Multiplier, divider.

    23. What are the limitations of the basic differentiator circuit? A differentiator may oscillate and become unstable at high frequencies, and input impedance decreases as frequency increases.

    24. What are the restrictions of the fundamental Integrator circuit? An Integrator may oscillate and become unstable at low frequencies, and its input impedance decreases as frequency increases.

    25. A comparator is a device that compares a signal to a predetermined reference voltage. its output is either + Vsat or -Vsat .

    26. What are the applications of comparator? Zero crossing detector

    27. If noise exists in sinusoidal signal at zero volts unintentionally, output varies between + Vsat and -Vsat. Why can’t we use comparator to convert sin wave into square wave?

    28. What is a Schmitt trigger? It is a regenerative comparator. It converts sinusoidal input into a square wave output.

    29. A multivibrator is a type of regenerative circuit widely used in timing applications. Depending on the type of multivibrator, it can exist in either a stable or quasi-stable state.

    30. A monostable multivibrator is a device that responds to each external trigger signal with a single pulse of a predetermined duration. It has only one stable state. Its is also called as One-shot generator.

    31. An astable multivibrator is an oscillator that runs freely and has two quasi-stable states. So it is a Square wave generator.

    32. What is a bistable multivibrator?

    Without an external trigger, a bistable multivibrator maintains a specific output voltage level. When an external trigger signal is applied, the state changes, and the output level remains unchanged until a subsequent trigger is applied. As a result, before it returns to its initial state, it needs two external triggers.

    33. What conditions must be met in order to create sustained oscillations in feedback circuits?

  • The total phase shift around the loop must be zero
  • the magnitude of the loop gain should be equal to unity
  • 34. What are the different types of oscillators? RF oscillator: Colpitts oscillator, Hartley oscillator, RC phase shift oscillator

    35. A filter is a frequency-selective circuit that passes signals within a specific frequency band while attenuating signals from frequencies outside of the band.

    35. What are the drawbacks of passive filters? Their roll off is lower and their maximum gain is unity.

    36. Active filters have the advantages of having a high input impedance and a low output impedance, which increases the load drive capacity. Roll off is greater than 1, pass band gain is greater

    37. What are the various filters?

  • Low pass filter
  • High pass filter
  • Band pass filter
  • Band reject filter.
  • 38. All signals are passed through the all-pass filter to the output, but it also provides a phase difference of 0 to 90 degrees.

    39. What Does Filter Order Represent? Filter Order Represents No a system’s (circuit’s) storage components as order rises and roll off rises

    40. The frequency at which the ratio of the (input/output) has a magnitude of 0 is known as the cutoff frequency. 707. When this magnitude is converted to decibels, the 3dB down point is commonly used.

    41. Radar synchronization, satellite communication systems, airborne navigational systems, FM communication systems, etc. are all applications where PLL is frequently used.

    42. Phase detector/comparison, Low pass filter, error amplifier, and voltage controlled oscillator are the fundamental components of a PLL.

    43. The three phases of PLL operations are free running, capture, and locked/tracking.

    44. Define the terms “lock-inrange,” “capture range,” and “pull-in time” for a PLL. * The lock-in range, also known as the tracking range, is the range of frequencies over which the PLL can maintain lock with the incoming signal. *The capture range is the range of frequencies over which the PLL can lock onto an input signal. Pullintime is the amount of time required by the PLL to establish lok. It is influenced by the initial phase and frequency difference between the two signals, as well as the characteristics of the loop filter and the overall loop gain.

    45. A voltage controlled oscillator is a free running multivibrator that runs at a specific frequency known as the free running frequency. By applying a dc control voltage, this frequency can be moved to either side, and the frequency deviation is proportional to the dc control voltage.

    46. The external timing resistor, RT, external timing capacitor, CT, and the dc control voltage, Vc, are the variables that determine the free running frequency of the VCO.

    47. Give the expression for the VCO free running frequency. fo = 0. 25 / Rt Ct.

    48. Mention some typical applications of PLL:

  • Frequency multiplication/division
  • Frequency translation
  • AM detection
  • FM demodulation
  • FSK demodulation.
  • Viva Questions on ADC, DAC:

    1. List the broad classification of ADCs. Direct type ADC. Integrating type ADC.

    2. List out the direct type ADCs. 1. Flash type converter 2. Counter type converter 3. Tracking or servo converter 4. Successive approximation type converter.

    3. List out some integrating type converters. 1. Charge balancing ADC 2. Dual slope ADC.

    4. What is an integrating type converter? An integrating type A/D converter is an ADC converter that performs conversion in an indirect manner by first converting the analog I/P signal to a linear function of time or frequency and then to a digital code.

    5. Briefly describe the successive Approximation ADC’s operating principle. The successive approximation register (SAR) in the successive approximation ADC circuit is used to iteratively determine the required value for each bit. When the START command arrives, SAR sets the MSB bit to 1. The O/P signal is analogized and compared to the I/P signal. This O/P is low or High. This process continues until all bits are checked.

    6. What are the main advantages of integrating type ADCs? i. The sample/Hold circuit at the input is not necessary for the integrating type of ADCs. ii. Even in a busy environment or in an isolated form, it is possible to transmit frequency.

    7. The successive approximation type ADCs are utilized in applications such as data loggers and instrumentation where conversionspeed is crucial.

    8. The primary disadvantage of a dual slope ADC is its lengthy conversion time. This is the main drawback of dual slope ADC.

    9. The dual slope ADC has the following benefits: It offers excellent noise rejection for ac signals whose periods are integral multiples of the integration time T.

    10. Define conversion time. how long it takes to fully transform an analog signal into its digital output

    11. Define resolution of a data converter. The smallest change in analog input for a one bit change at the output is considered an ADC’s resolution.

    12. The linearity of an ADC/DAC is a crucial indicator of its accuracy and informs us of how closely the converter output adheres to its intended transfer characteristics.

    13. A monotonic DAC is one whose analog output rises in proportion to an increase in digital input.

    14. A sample and hold circuit samples an input signal and holds onto the most recent sampled value until the input is sampled again. What is it used for? This is mainly used in analog to digital conversion.

    15.Explain the various types of digital to analog converters?

  • Weighted resistor DAC
  • R2R ladder DAC
  • Inverted R2R ladder DAC
  • 6. Which circuit serves as the active load for an amplifier? (A) Wildar Current source (B) Darlington pair (C) Current Mirror (D) All of the above (Explanation)) View AnswerAnswer: c (Explanation) Current mirror has DC resistance (order of few k), as quiescent voltage across it is a fraction of supply voltage and current in milliamperes.

    7. Which of the following best describes the equation for the load current in a differential amplifier with an active load? a) IL = gmvd b) IL = Iq /2 c) IL = Iq(Vin1 – Vin2) d) IL = 2gm/(Vin1 – Vin2) View AnswerAnswer: a Explanation: The load current is given as the product of difference between input & output voltage and trans As a result, IL = gmvd is the equation for load current.

    1. View AnswerAnswer: c Explanation: Darlington pair can be used in the differential amplifier’s place of the transistor to increase the input resistance. This is because Darlington pair has a higher value of input resistance than the transistor.

    2. The current gain in a Darlington pair differential amplifier is specified as 100. Where IB1=5µA and IC1=0. 35mA. Determine IC2 a) 0. 5mA b) 1. 5mA c) 2mA d) 0. Explanation: The current gain in a Darlington pair differential amplifier is given as =(IC1+IC2)/IB1. 15mA View AnswerAnswer: d Substituting the values in the equation, we get IC2=(β×IB1)-IC1 =(100×5µA)-0. 35mA =0. 15mA.

    3. Find the overall current gain in the circuit shown by choosing one of the following options: a) 456218; b) 444878; c) 444210; d) 455734. 6µA. IE1= IB1+ IC1 = 1. 43mA + 5. 6µA = 1. 435mA. IE1= IB2 = 1. 435mA. Individual current gain values are 1=IC1/IB1 and 1 = 1. 43mA/5. 6µA= 255. 36. Similarly,β2=IC2/ IB2 => β2 = 2. 5A / 1. 435mA =1742. 16 As a result, the total current gain is = 1 2 = 255. 36 × 1742. 16 = 444878.

    The reason why the IC 55 timer has that name is because it uses three resistors, each measuring 5k ohms.

    Answer: A voltage known as noise voltage is produced by the random movement of electrons inside any electronic device, such as a resistor. This noise voltage is amplified by the amplifier and feedback. The output will experience sustained oscillations if the Barkhausen criterion is met. Thus, oscillators can run without an input signal because noise voltage serves as the starting voltage.

    An analog solid state device called a linear integrated circuit has a theoretically infinite number of possible operating states. It operates over a continuous range of input levels. The amplification curve of a linear IC is a straight line within a specific input range. e. the input and output voltages are directly proportional. Operational amplifier, also known as an op amp, is the most popular common linear IC.

    In hybrid integrated circuits, the interconnections between passive components (like resistors and capacitors) are formed on an insulating substrate. Then, to create a complete circuit, active components like diodes and transistors as well as monolithic integrated circuits are connected.

    The dc level at the emitters rises from stage to stage due to direct coupling. The operating point of the succeeding stage is shifted by this increase in DC level, which limits the output voltage swing and may even cause output signal distortion. Therefore, level translator circuits are used to raise this dc level.


    What is the use of linear integrated circuits?

    Solid state analog linear integrated circuits can function with a wide range of input signals. They have an infinite number of operating states, according to theory. Linear Integrated Circuits are widely used in amplifier circuits.

    What is called linear integrated circuit?

    A linear integrated circuit, also known as an analog chip, is a collection of tiny electronic analog circuits assembled on a single semiconductor piece.

    Why linear integrated circuit is called linear?

    Because the output voltage and current of such a circuit are linear functions of its input voltage and current, it is known as a linear circuit. This type of linearity is different from that found in graphs with straight lines.

    What is bird’s beak in linear integrated circuit?

    Growing a thin SiO2 layer before applying the Si3N4 mask can significantly lessen this damage. Typically 100 to 200Ao is used for this purpose. Unfortunately, this significantly speeds up the penetration of oxide beneath the nitride-masked areas, leading to oxide configurations known as “bird’s beak” configurations.

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