ELECTRONICS AND COMMUNICATION ENGINEERING INTERVIEW QUESTIONS AND ANSWERS

What Is Op­-amp?

An operational amplifier, often called an op­-amp , is a DCcoupled high ­gain electronic voltage amplifier with differential inputs and, usually, a single output. Typically the output of the op­amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation.

Different types of communications? Explain.

Analog and digital communication.
As a technology, analog is the process of taking an audio or video signal (the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of “1”s and “0”s.
Digital signals are immune to noise, quality of transmission and reception is good, components used in digital communication can be produced with high precision and power consumption is also very less when compared with analog signals.

What is sampling?

The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.

What Is Transistor?

In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all other modernelectronic devices. Some transistors are packaged individually but most are found in integrated circuits.

State sampling theorem.

It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.

What Is Diode?

In electronics, a diode is a two­terminal device. Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property.

What is cut-off frequency?

The frequency at which the response is -3dB with respect to the maximum response.

What Is A Semi Conductor?

A semiconductor is a solid material that has electrical conductivityin between that of a conductor and that of an insulator(AnInsulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductorswithout passing current through itself); it can vary over that wide range either permanently or dynamically.

What is latch up?


Latch-up pertains to a failure mechanism wherein a parasitic thyristor (such as a parasitic silicon controlled rectifier, or SCR) is inadvertently created within a circuit, causing a high amount of current to continuously flow through it once it is accidentally triggered or turned on. Depending on the circuits involved, the amount of current flow produced by this mechanism can be large enough to result in permanent destruction of the device due to electrical overstress (EOS)

What Is Inductor?

An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An inductor can take many forms.

What is pass band?

Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.

What is stop band?

A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.

What Is Capacitor?

A capacitor is an electrical/electronic device that can store energyin the electric field between a pair of conductors (called “plates”). The process of storing energy in the capacitor is known as “charging”, and involves electric charges of equal magnitude, but opposite polarity, building up on each plate. 
Capacitors are often used in electric and electronic circuits asenergy­storage devices. They can also be used to differentiate between high­frequency and low­frequency signals. This property makes them useful in electronic filters.

Capacitors are occasionally referred to as condensers. This term is considered archaic in English, but most other languages use acognate of condenser to refer to a capacitor.

What Is A Rectifier?

A rectifier changes alternating current into direct current. This process is called rectification. The three main types of rectifier are the half­wave, full­wave, and bridge. A rectifier is the opposite of an inverter, which changes direct current into alternating current. HWR­ The simplest type is the half­wave rectifier, which can be made with just one diode. When the voltage of the alternating current is positive, the diode becomes forwardbiased and current flows through it. When the voltage is negative, the diode is reverse­biased and the current stops.

The result is a clipped copy of the alternating current waveform with only positive voltage, and an average voltage that is one third of the peak input voltage. This pulsating direct current is adequate for some components, but others require a more steady current. This requires a full­wave rectifier that can convert both parts of the cycle to positive voltage.

FWR­ The full­wave rectifier is essentially two half­wave rectifiers, and can be made with two diodes and an earthed centre tap on the transformer. The positive voltage half of the cycle flows through one diode, and the negative half flows through the other. The centre tap allows the circuit to be completed because current cannot flow through the other diode. The result is still a pulsating direct current but with just over half the input peak voltage, and double the frequency.

Explain RF?

Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits or electromagnetic radiation.

What is modulation? And where it is utilized?

Modulation is the process of varying some characteristic of a periodic wave with an external signals.
Radio communication superimposes this information bearing signal onto a carrier signal.
These high frequency carrier signals can be transmitted over the air easily and are capable of travelling long distances.
The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal.
Modulation is utilized to send an information bearing signal over long distances.

What is demodulation?

Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to base-band.

Name the modulation techniques.

For Analog modulation–AM, SSB, FM, PM and SM
Digital modulation–OOK, FSK, ASK, Psk, QAM, MSK, CPM, PPM, TCM, OFDM

What Is An Integrated Circuit?

An integrated circuit (IC), also called a microchip, is an electronic circuit etched onto a silicon chip. Their main advantages are low cost, low power, high performance, and very small size.

What Is A Transducer And Transponder?

A transducer is a device, usually electrical, electronic, electro­mechanical, electromagnetic, photonic, or photovoltaic that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer.

In telecommunication, the term transponder (shortforTransmitter­responder and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) has the following meanings:

  1. An automatic device that receives, amplifies, andretransmits a signal on a different frequency (see alsobroadcast translator).
  2. An automatic device that transmits a predetermined messagein response to a predefined received signal.
  3. A receiver­transmitter that will generate a reply signal upon proper electronic interrogation.
  4. A communications satellite’s channels are called transponders, because each is a separate transceiver or repeater.

What is ionospheric bending?

When a radio wave travels into the ionospheric layer it experiences refraction due to difference in density. The density of ionospheric layer is rarer than the layer below which causes the radio wave to be bent away from the normal. Also the radio wave experiences a force from the ions in the ionospheric layer. If incident at the correct angle the radio wave is completely reflected back to the inner atmosphere due to total internal reflection. This phenomenon is called ionospheric reflection and is used in mobile communication for radio wave propagation also known as ionospheric bending of radio waves.

What Is Oscillator?

An oscillator is a circuit that creates a waveform output  from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.

What is CDMA?

CDMA stands for Code Division Multiple Access which uses digital format. In CDMA systems several transmissions via the radio interface take place simultaneously on the same frequency bandwidth. User data is combined at the transmitter’s side with a code, then transmitted. On air, all transmission get mixed. At the receiver’s side the same code is used as in the transmitter’s side. The code helps the receiver to filter the user information of the transmitter from incoming mixture of all transmissions on the same frequency band and same time.

 

Explain AM and FM.

AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information bearing signal.
FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.

What is the principle of microwave?


Microwave essentially means very short wave. The microwave frequency spectrum is usually taken to extend from 1GHZ to 30GHZ. The main reason why we have to go in for microwave frequency for communication is that lower frequency band are congested and demand for point to point communication continue to increase. The propagation of the microwave takes place in spacewave in v

How many satellites are required to cover the earth?

3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span of the satellite is about 15 years.

What Is A Feedback? And Explain Different Types Of Feedback.

Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. This is often used to control the dynamic behaviour of the system.

Types of feedback:

Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation). Negative feedback feeds part of a system’s output, inverted, into the system’s input; generally with the result that fluctuations are attenuated.

Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as “cumulative causation”, is a feedback loop system in which the system responds to perturbation (Aperturbation means a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as the perturbation. In contrast, a system that responds to the perturbation in the opposite direction is called a negative feedback system. 

Bipolar feedback: which can either increase or decrease output.

What is demodulation?

Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to base-band.

What are GPRS services?

GPRS services are defined to fall in one of the two categories :

– PTP ( Point to point)
– PTM ( Point to Multipoint)
Some of the GPRS services are not likely to be provided by network operators during early deployment of GPRS due in part to the phased development of standard. Market demand is another factor affecting the decision of operators regarding which services to offer first.

What Is Multiplexing?

Multiplexing (known as muxing) is a term used to refer to a processwhere multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire.

What Is A Repeater?

A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.

What Is Attenuation?

  1. Attenuation is the reduction in amplitude and intensity of a signal. Signals may attenuate exponentially by transmission through a medium, or by increments calculated in electronic circuitry or set by variable controls.
  2. Attenuation is an important property in telecommunications and ultrasound applications because of its importance in determining signal strength as a function of distance. 
  3. Attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in question.

What are the advantages of spread spectrum?

SPread spectrum has the following advantages :

1. No crosstalk interference.
2. Better voice quality/data integrity and less static noise.
3. Lowered susceptibility to multipath fading.
4. Inherent security.
5. Co-existence.
6. Longer operating distances.
7. Hard to detect.
8. Hard to intercept or demodulate.
9. Harder to jam than narrow bands.
10. Use of ranging and radar.

What Is Stop Band?

A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.

What Is Pass Band?

Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.

State Sampling Theorem.

It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.

What Is Sampling?

The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.

Explain AM and FM.

AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information bearing signal.
FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.

Explain Bluetooth.

Bluetooth is designed to be a personal area network, where participating entities are mobile and require sporadic communication with others. It is Omni directional i.e. it does not have line of sight limitation like infra red does. Ericsson started the work on Bluetooth and named it after the Danish king Harold Bluetooth. Bluetooth operates in the 2.4 GHz area of spectrum and provides a range of 10 meters. It offers transfer speeds of around 720 Kbps.

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