Top 37 Amplifier Interview Questions You Must Prepare 02.Mar.2024

An operational amplifier, abbreviated as op-amp, is basically a multi-stage, very high gain, direct-coupled, negative feedback amplifier that uses voltage shunt feedback to provide a stabilized voltage gain.

Integrators are widely used in ramp or sweep generators, filters, analog computers etc.

Assumptions made for analyzing ideal op-amp are:

  • Infinite open-loop gain
  • Infinite input impedance
  • Zero output impedance
  • Perfect balance
  • Infinite frequency bandwidth
  • Infinite slew rate
  • Infinite common-mode rejection ratio
  • Nil drift of characteristics with temperature

The zero signal values of IC and VCE are known as the operating point. It is called operating point because the variations of IC and VCE take place about this point when signal is applied. It is also known as the quiescent or Q-point.

When the input signal is quite weak and produces less small fluctuations in the output current in comparison to its quiescent value, the amplifier is called the small signal or voltage amplifier.

Amplifier is a device that makes sound louder and signal level greater.

OPAMP it is a direct coupled high gain differential input amplifier. It is called operational amplifier because it is used for performing different functions like differentiation, addition, integration, subtraction. It has infinite voltage gain, infinite slew rate, infinite input impedance, zero output impedance, infinite bandwidth.

Adder, subtractor, differentiator, integrator fall under the category of linear circuits.

The proper flow of zero signal collector current and the maintenance of proper collector emitter voltage during the passage of signal is called the tristor biasing.

The process of raising the strength of a weak signal without any change in its general shape is referred to as faithful amplification.

The formula for non inverting amplifier is given as 1+Rf/R1.

For a common collector amplifier, current gain is as high as for CE amplifier, voltage gain is less than unity, input resistance is the highest and the output resistance is the lowest of all the three (CE, ,CC and CB) configurations. This circuit finds wide applications as a buffer amplifier between a high impedance source and a low load.

Input offset voltage may be defined as that voltage which is to be applied between the input terminals to balance the amplifier.

CMRR is defined as the ratio of differential voltage gain to common-mode voltage gain and it is given as CMRR = Ad/Acm.

Characteristic of ideal OP AMP are

  1. Infinite voltage gain
  2. Zero output impedance
  3. Infinite input impedance
  4. Infinite slew rate
  5. Characteristics not drifting with temperature
  6. Infinite bandwidth

Op-amp is used mostly as an integrator than a differentiator because in differentiator at high frequency, gain is high and so high-frequency noise is also amplified which absolutely abstract the differentiated signal.

In an inverting amplifier, the input is connected to the minus or inverting terminal of op-amp.

Adder or summing amplifier is a circuit that provides an output voltage proportional to or equal to the algebraic sum of two or more input voltages multiplied by a constant gain factor.

When an op-amp is operated in the open-loop configuration, the output either goes to positive saturation or negative saturation levels or switches between positive and negative saturation levels and thus clips the output above these levels. So open-loop op-amp configurations are not used in linear applications.

When the difference of the two inputs applied to the two terminals of a differential amplifier is amplified, the resultant gain is termed as differential gain. But when the two input terminals are connected to the same input source then the gain established by the differential amplifier is called the common mode gain.

Voltage follower is an electronic circuits in which output voltage tracts the input voltage both in sign and magnitude.

The CC circuit amplifier is called an emitter follower because in this circuit the output voltage at the emitter terminal follows the input signal applied to the base terminal.

High CMRR ensures that the common mode signals such as noise are rejected successfully and the output voltage is proportional only to the differential input voltage.

Removal of bypass capacitor in a CE amplifier circuit causes excessive degeneration in the amplifier circuit and therefore reduction in voltage gain.

Voltage follower has three unique characteristics viz. extremely high input impedance, extremely low output impedance and unity trmission gain and is , therefore, an ideal circuit device for use as a buffer amplifier.

The dynamic resistance of the emitter-base junction diode is called the ac emitter resistance.

Slew rate of an op-amp is defined as the maximum rate of change of output voltage per unit time and is expresses in V/µs.

If feedback resistor is made zero or R1 is made ∞(by keeping it open-circuited) in a noninverting amplifier circuit, voltage follower is obtained.

Differential amplifier is a combination of inverting and noninverting amplifiers and amplifies the voltage difference between input lines neither of which is grounded.

OPAMP is called direct coupled because the input of one OPAMP is inserted into the input of another OPAMP. It is called high gain differential circuit because the difference of the two input is amplified.

Inverting amplifier is a very versatile component and can be used for performing number of mathematical stimulation such as analog inverter, paraphrase amplifier, phase shifter, adder, integrator, and differentiator.

The parameters to be considered for dc applications are:

  • Input offset voltage
  • Input offset current
  • Input bias current
  • Drift

The parameters to be considered for ac applications are:

  • Gain bandwidth product (GBW)
  • Rise time
  • Slew rate
  • Full-power response
  • AC noise

Perfect balance is the characteristics of ideal OP AMP and if there is same input applied then we will get the output zero. In this condition it is known as perfect balance.

CMRR is defined as the ratio of differential voltage gain (Ad) to common mode voltage gain (Acm).

The formula for CMRR is given below:

CMRR = Ad/Acm

If Acm will be zero then only it will be infinite.

In a CE configuration, the output voltage increases in the negative direction when the input signal voltage increases in the positive direction and vice-versa. This is called the phase reversal and and causes a phase difference of 180o between the input signal and output voltage.

If we give the sinusoidal input in differentiator we will get the output of differentiator as a square output. If we give the sinusoidal input in integrator we will get the output of integrator as a ramp output.

An integrator is a circuit that performs a mathematical operation called integration.