ELECTRONICS INTERVIEW QUESTIONS AND ANSWERS

Q. What is Biasing?
Ans- Biasing is process of applying potential across any electronic equipment in order to make it operate as we require.

Q. What is the frequency of RC phase shift oscillator?
Ans. To find resonant frequency of an RC phase shift oscillator, use the following formula

 f=1/2πRC√6

Q. What is a phase shift oscillator?
Ans. “Phase shift oscillator” is the term given to a particular oscillator circuit topology that uses an RC network in the feedback loop of a tube, transistor, or opamp to generate the required phase shift at a particular frequency to sustain oscillations. They are moderately stable in frequency and amplitude, and very easy to design and construct.

 

Q. Why RC oscillators cannot generate high frequency oscillations?
Ans. At high frequencies, resistors look like inductors or capacitors so the equations that govern oscillation in RC oscillators no longer apply. In other words, because of those parasitic components, it gets more and more difficult to make a stable RC oscillator as frequencies go up. At some point it becomes easier and more stable to use other types of oscillators.

Q. What are the applications of RC phase shift oscillators?
Ans. RC phase shift oscillators are mostly used at audio frequencies. Other than this, electronic organs makes use of this oscillator such as electronic musical instruments like pianos.

Also used in equipment that emits beeps. Example, many GPS units beeps when they performs an action.

Also used in voice synthesis.

Q. what phase shift does RC phase shift oscillator produce?
Ans. RC phase shift oscillator produces a phase shift of 180 degrees between output and input signal. In the phase-shift oscillator, at least three RC sections are needed to give the required 180-degree phase shift for regenerative feedback. The values of resistance and capacitance are generally chosen so that each section provides about a 60-degree phase shift.

Q. Why we need a phase shift between input and output signal?
Ans. To obtain the regenerative feedback in the phase-shift oscillator, we need a phase shift of 180 degrees between the output and the input signal. An RC network consists of three RC sections which provides the proper feedback and phase inversion to provide this regenerative feedback. Each section shifts the feedback signal 60 degrees in phase.

Q. How is phase angle determined in RC phase shift oscillator?
Ans. Since the impedance of an RC network is capacitive, the current flowing through it leads the applied voltage by a specific phase angle. The phase angle is determined by the amount of resistance and capacitance of the RC section. If the capacitance is a fixed value, a change in the resistance value will change the phase angle. If the resistance could be changed to zero, we could get a maximum phase angle of 90 degrees. But since a voltage cannot be developed across zero resistance, a 90-degree phase shift is not possible.

Q. How can we get a maximum phase angle of 90 degrees in RC phase shift oscillator?
Ans. By changing the resistance to zero, we can get a maximum phase angle of 90 degrees. But since we cannot develop voltage across zero resistance, so a 90 degree phase shift is not possible.

Q.What is CMRR

Ans  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

QWhat is characteristic of Ideal OPAMP? 

Ans Characteristic of ideal OPAMP 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

Q.What is Amplifier? 

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

Q. What is the Formula for Non Inverting Amplifier?

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

Q. What is perfect balance in OPAMP? 

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

Q. What Which OPAMP don’t have feedback loop?

Ans Comparator OPAMP (operational amplifier) don’t  have feedback loop.

Q.Why OPAMP called direct coupled high differential circuit?

Ans  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.

Q. Why OPAMP called operational Amplifier? Important Interview questions on OPAMP

Ans 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.

Q. What is the output Differentiator and Integrator

Ans 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.

Q.  For the CMRR to be infinite what will be the condition? 

Ans 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 

 

Q.     What are the advantages between positive and negative feedback?

The positive feedback has the only advantage of its gain being higher than the negative feedback where as the negative feedback has quite some advantages like high stability, less noise and high bandwidth.

Q.  What is the difference between Amplitude and Frequency Modulation?

Amplitude Modulation is the process where the amplitude of the carrier signal is varied with respect to the information signal and in frequency modulation process, the frequency of the carrier signal is varied along with the information signal.

Q.What is an operational amplifier?

Popularly known as op-amp, the operational amplifier is an electronic voltage amplifier where the dc is coupled for high gain. Differential inputs are given are given a single output is obtained depending upon the nature of the op-amp.

Q.What is known as a rectifier? What does it do?

A rectifier is merely a convertor which converts the alternating current to direct current. This process of conversion is called as rectifying. There are different types of rectifiers called as full-wave, half-wave and bridge rectifiers. It functions just as opposite to an inverter.

Q.   Explain in brief about the functioning a mobile technically.

The voice is converted into radio frequency signals and they are transmitted to the nearby base station. The signal is boosted in the base station for further transmission and it is transmitted from there through the telephone network to the desired mobile network.

 Q.      What is the main difference between a transponder and a transducer?

A transducer is a device which converts a particular type of energy to an electric signal. A transponder is a device which is a combination of both transmitter and receiver. This device is used to both transmit and receive signals. It is used to reduce the complexity of the unit.

Q.    What is known as a cross talk?

Cross talk is normally an interference that is resulted due to the placing of different conductors adjacently. It is a common phenomenon that occurs in radios, telephones etc.

 Q.     Explain in brief about attenuation.

Attenuation is the term that is used to describe the reduction in the signal strength and intensity. When signals are transmitted long distances, the attenuation is generally inversely proportional with the increase in distance. Signal boosters will be placed at regular intervals to enhance the intensity of the signals.

 Q.  What do you mean by multiplexing?

Multiplexing is also known as muxing which is the concept of combining different analog signals or digital data into one single signal to cut back on expenses. The receiver end will use a demultiplexer to separate this combined signal to the original form.

Q.  Mention the difference between CDMA and GSM.

CDMA is the abbreviation of code division multiple access where a particular code is given for particular network and the signals of the other networks will be ignored. GSM is the abbreviation of global system for mobile communication which works on TDMA where a single radio frequency is split into multiple time slots and is transmitted.

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