Electronics Communication Engineering viva Questions and Answers:

Following are the Basic and Advanced Electronics Communication Engineering viva Questions and Answers

Acceptor atoms Trivalent atoms that accept free electrons from pentavhalent atoms.

AC coupling Circuit that passes an AC signal while blocking a DC voltage.

AC/DC Equipment that will operate on either an AC or DC power source.

AC generator Device used to transform mechanical energy into AC electrical power.

AC load line A graph representing all possible combinations of AC output voltage and current for an amplifier.

Active component A component that changes the amplitude of a signal between input and output.

Active filter A filter that uses an amplifier in addition to reactive components to pass or reject selected frequencies.

Active region The region of BJT operation between saturation and cut-off used for linear amplification.

Alpha Ratio of collector current to emitter current in a Bipolar Junction Transistor (BJT). Greek letter alpha a is the symbol used.

Alternating current An electric current that rises to a maximum in one direction, falls back to zero and then rises to a maximum in the opposite direction and then repeats.

Amplifier A circuit that increases the voltage, current or power of a signal.

Analog Information represented as continuously varying voltage or current rather than in discrete levels as opposed to digital data varying between two discrete levels.

Antenna, transmitting A device that converts an electrical wave into an electromagnetic wave that radiates away from the antenna.

Antenna, receiving A device that converts a radiated electromagnetic wave into an electrical wave.

Apparent power Power attained in an AC circuit as a product of effective voltage and current which reach their peak at different times.

Astable multivibrator An oscillator that produces a square wave output from a DC voltage.

Balanced bridge Condition that occurs when a bridge circuit is adjusted to produce a zero output.

Band-pass filter A tuned circuit designed to pass a band of frequencies between a lower cut-off frequency (f₁) and a higher cut-off frequency (f₂). Frequencies above and below the pass band are heavily attenuated.

Band-stop filter A tuned circuit designed to stop frequencies between a lower cut-off frequency (f₁) and a higher cut-off fiequency (f₂) of the amplifier while passing all other frequencies.

Barrier potential The natural difference of potential that exists across a forward biased p-n junction.

Baud rate A unit of signalling speed equal to the number of signal events per second. Not necessarily the same as bits per second.

Beta The ratio of collector current to base current in a Bipolar Junction Transistor (BJT).

Bipolar Junction Transistor (BJT) A three terminal device in which emitter to collector current is controlled by base current.

Bistable multivibrator A multivibrator with two stable states. An external signal is required to change the output from one state to the other. Also called a latch

Bode plot A graph of gain versus

Breakdown voltage Voltage at which the breakdown of a dielectric or insulator occurs.

Break over voltage Minimum voltage required to cause a diac to break down and conduct.

Bridge rectifier A circuit using four diodes to provide full wave rectification. Converts an AC voltage to a pulsating DC voltage.

Buffer An amplifier used to isolate a load from a source.

Butterworth filter A type of active filter characterized by a constant gain (flat response) across the mid-band of the circuit and a 20 dB per decade roll-off rate for each pole contained in the circuit.

Cathode Ray Tube (CRT) Vacuum tube used to display data in a visual Picture tube of a television or computer terminal.

Centre tapped rectifier Circuit that make use of a centre tapped transformer and two diodes to provide full wave rectification.

Centre tapped transformer A transformer with a connection at the electrical centre of a winding.

Clamper A diode circuit used to change the DC level of a waveform without distorting the waveform.

Class A amplifier A linear amplifier biased so the active device conducts through 360 degrees of the input waveform.

Class B amplifier An amplifier with two active devices. The active components are biased so that each conducts for approximately 180 degrees of the input waveform cycle.

Class C amplifier An amplifier in which the active device conducts for less than 180 degrees of the input waveform cycle.

Clipper A diode circuit used to eliminate part of a waveform

Collector The semiconductor region in a bipolar junction transistor through which a flow of charge carriers leaves the base region.

Common base amplifier A BJT circuit in which the base connection is common to both input and output.

Common collector amplifier A BJT circuit in which the collector connection is common to both input and output.

Common drain amplifier A FET circuit in which the drain connection is common to both input and output.

Common emitter amplifier A BJT circuit in which the emitter connection is common to both input and output.

Common gate amplifier A FET circuit in which the gate connection is common to both input and output.

Common source amplifier A FET circuit in which the source connection is common to both input and output.

Common-Mode Rejection Ratio (CMRR) The ratio of op-amp differential gain to common-mode gain. A measure of an op-amp’s ability to reject common-mode signals such as noise.

Covalent bond The way some atoms complete their valence shells by sharing valence electrons with neighbouring atoms.

Cut-off frequency Frequency at which the power gain of an amplifier falls below 50% of maximum.

Damping Reduction in magnitude of oscillation due to energy being dissipated as heat.

Darlington pair An amplifier consisting of two bipolar junction transistors with their collectors connected together and the emitter of one connected to the base of the other.

Depletion mode In a FET, an operating mode where reverse gate-source voltage is used to deplete the channel of free carriers. This reduces the size of the channel and increases its resistance.

Depletion-mode MOSFET A MOSFET designed to operate in either depletion mode or enhancement mode.

Device A component or part.

Diac A two terminal bidirectional thyristor. Has a symmetrical switching mode.

Differential amplifier An amplifier in which the output is in proportion to the differences between voltages applied to its two inputs.

Differentiator A circuit in which the output voltage is in proportion to the rate of change of the input voltage. A high pass RC circuit.

Diffusion Tendency of conduction band electrons to wander across a p-n junction to combine with valence band holes.

Diode A two terminal device that conducts in only one direction.

Donor atoms Pentavalent atoms that give up electrons to the conduction band in an n – type semiconductor material.

Doping The process of adding impurity atoms to intrinsic (pure) silicon or germanium to improve the conductivity of the semiconductor material.

Dot convention Standard used with transformer symbols to indicate whether the secondary voltage is in phase or out of phase with the primary voltage.

Drift A problem that can develop in tuned amplifiers when the frequency of the tuned circuit changes due to temperature or component aging.

Eddy currents Currents induced into a conducting core due to the changing magnetic field. Eddy currents produce heat which is a loss of power and lowers the efficiency of an inductor.

Efficiency The amount of power delivered to the load of an amplifier as a percentage of the power required from the power supply.

Electromechanical transducer Device that transforms electrical energy into mechanical energy (electric motor) or mechanical energy into electrical energy (generator).

Electromotive force (emf) Force that causes the motion of electrons due to potential difference between two points. (voltage)

Emitter The semiconductor region from which charge carriers are injected into the base of a bipolar junction transistor.

Emitter feedback Coupling from the emitter output to the base input of a bipolar junction transistor.

Emitter follower A common collector amplifier. Has a high current gain, high input impedance and low output impedance.

Feedback amplifier An amplifier with an external signal path from its output back to its input.

Field Effect Transistor (FET) A voltage controlled transistor in which the source to drain conduction is controlled by gate to source voltage.

Filter Network consisting of capacitors, resistors and/or inductors used to pass certain frequencies and block others.

Flip flop A bistable multivibrator. A circuit which has two output states and is switched from one to the other by means of an external signal (trigger).

Forward bias A p-n junction bias which allows current to flow through the Forward bias decreases the resistance of the depletion layer.

Frequency-Division Multiplex (FDM) Transmission of two or more signals over a common path by using a different frequency band for each signal.

Frequency-domain analysis A method of representing a waveform by plotting its amplitude against frequency.

Full Scale Deflection (FSD) Deflection of a meter’s pointer to the farthest position on the scale.

Full wave rectifier Rectifier that makes use of the full AC wave in both the positive and negative half cycles.

H-parameters (hybrid parameters) Transistor specifications that describe the component operating limits under specific circumstances.

Half wave rectifier A diode rectifier that converts AC to pulsating DC by eliminating either the negative or the positive alternation of each input AC cycle.

Harmonic Sine wave that is smaller in amplitude and some multiple of a fundamental frequency.

Hartley oscillator An oscillator that uses a tapped inductor in the feedback

High-pass filter A tuned circuit designed to pass all frequencies above a designated cut-off frequency. Frequencies below the cut-off frequency are rejected or attenuated.

Hybrid circuit Circuit that combines two technologies (passive and active or discrete and integrated components) onto one microelectronic circuit.

Integrator A device that approximates and whose output is proportional to an integral of the input signal. A low pass filter.

Intermediate frequency amplifier In a super heterodyne radio it amplifies a fixed frequency lower than the received radio frequency and higher than the audio frequency.

Inverting amplifier An amplifier that has a 180° phase shift from input to output.

Inverting input In an operational amplifier (op-amp) the input that is marked with a minus sign. A signal applied at the inverting input will be given 180° phase shift between input and output.

Knee voltage The voltage at which a curve joins two relatively straight portions of a characteristic curve. For a p-n junction diode, the point in the forward operating region of the characteristic curve where conduction starts to increase For a zener diode, the term is often used in reference to the zener voltage rating.

Laser Device that produces a very narrow intense beam of light. The name is an acronym for “ight amplification by stimulated emission of radiation.”

Light-emitting diode A semiconductor diode that converts electric energy into electromagnetic radiation at a visible and near infrared frequencies when its p-n junction is forward biased.

Low pass filter A tuned circuit designed to pass all frequencies below a designated cut-off frequency.

Maximum power transfer A theorem that states that maximum power will be transferred from source to load when input impedance of the load equals the output impedance of the source.

Metal Oxide Field Effect Transistor (MOSFET) A field effect transistor in which the insulating layer between the gate electrode and the channel is a metal oxide layer.

Miller’s theorem A theorem that allows you to represent a feedback capacitor as equivalent input and output shunt capacitors.

Modulation Process by which an information signal (audio for example) is used to modify some characteristic of a higher frequency wave known as a carrier (radio for example).

Monostable multivibrator A multivibrator with one stable output state. When triggered, the circuit output will switch to the unstable state for a predetermined period of time and then return to the stable state.

Multivibrator A class of circuits designed to produce square waves or

n-type semiconductor A semiconductor compound formed by doping an intrinsic semiconductor with a pentavalent element. An n-type material contains an excess of conduction band electrons.

Noise Unwanted electromagnetic radiation within an electrical or mechanical system.

Non-inverting input The terminal of an operational amplifier that is identified by a plus sign.

Norton’s theorem Any network of voltage sources and resistors can be replace by a single current source in parallel with a single resistor.

n-p-n transistor A bipolar junction transistor in which a p-type base element is sandwiched between an n-type emitter and an n-type collector.

Ohm’s law Relationship between voltage, current and resistance. Ohm’s law states that current in a resistance varies in direct proportion to voltage applied and inversely proportional to resistance.

Kirchhoff’s current law The sum of the currents flowing into a point in a circuit is equal to the sum of the currents flowing out of that same point.

Kirchhoff’s voltage law The algebraic sum of the voltage drops in a closed path circuit is equal to the algebraic sum of the source voltages applied.

Operational amplifier A high gain DC amplifier that has a high input impedance and a low output impedance. Op-amps are the most basic type of linear integrated circuits.

Pass band The range of frequencies that will be passed and amplified by a tuned amplifier. Also the range of frequencies passed by a band pass filter.

Passive component Component that does not amplify a signal. Resistors and capacitors are examples.

Peak Inverse Voltage (PIV) The maximum rated value of AC voltage acting in the direction opposite to that in which a device is designed to pass current.

Phase shift oscillator An oscillator that uses three RC networks in its feedback path to produce the 180° phase shift required for oscillation.

Photodiode A semiconductor diode that changes its electrical characteristics in response to illumination.

Photovoltaic cell Component commonly called a solar cell used to convert light energy into electrical energy.

Pinch-off region A region on the characteristic curve of a FET in which the gate bias causes the depletion region to extend completely across the channel.

Positive feedback A feedback signal that is in phase with an amplifier input Positive feedback is necessary for oscillation to occur.

Power amplifier An amplifier designed to deliver maximum power output to a load.

MOSFET Abbreviation for “metal oxide field effect transistor” also known as an “insulated gate field effect transistor). A field effect transistor in which the insulating layer between the gate electrode and the channel is a metal oxide layer.

Power factor Ratio of actual power to apparent power.

Power loss Ratio of power absorbed to power delivered.

Primary cell Cell that produces electrical energy through an internal electrochemical action. Once discharged a primary cell cannot be reused.

Propagation delay Time required for a signal to pass through a device or

Propagation time Time required for a wave to travel between two points.

Pulse repetition frequency The number of times per second that a pulse is transmitted.

Pulse repetition time Time interval between the start of two consecutive pulses.

R-2R ladder Network or circuit composed of a sequence of L networks connected in tandem. Circuit used in digital to analog converters.

Pulse rise time Time required for a pulse to increase from 10% of its peak value to 90% of its peak value.

Pulse width Time interval between the leading edge and trailing edge of a pulse at a point where the amplitude is 50% of the peak value.

Radar Acronym for Radio Detection And Ranging a system that measures the distance and direction of objects generally in space.

Radio-frequency amplifier Amplifier having one or more active devices to amplify radio signals.

Reactive power Also called imaginary power or wattless power. It is the power value in volt-amp obtained from the product of source voltage and source current in a reactive circuit.

Rectifier Diode circuit that converts alternating current into pulsating direct current.

Regulator Device or circuit that maintains a desired output under changing

Resonance Circuit condition that occurs at the frequency where inductive reactance (X_L) equals capacitive reactance (X_C).

Reverse breakdown voltage Amount of reverse bias that will cause a p-n junction to breakdown and conduct in the reverse direction.

Reverse saturation current Reverse current through a diode caused by thermal activity. This current is not affected by the amount of reverse bias on the component, but does vary with temperature.

Schmitt trigger Circuit to convert a given waveform to a square wave output.

Secondary cell tectrolytic, cell used to stire electricity. Once discharged may be restored by recharging by putting current through the cell in the direction opposite to that of discharge con ent

Semiconductor An element which is neither u ijood conductor or a good insulator, but rather lies somewhere between the two

Series resonance Condition that occurs in a series LC circuit at the frequency where inductive reactance equals capacitive reactance.

Single Sideband (SSB) AM radio communication technique in which the transmitter suppresses on.) sideband and therefore transmits only a single

Solar cell Photovoltaic cell that converts light into electric energy. Especially useful as a power source for space vehicles.

Step-down transformer Transformer in which the output AC voltage is less than the input AC voltage.

Step-up transformer Transformer in which the output AC voltage is greater than the input AC voltage.

Stop band Range of frequencies outside the pass band of a tuned amplifier.

Summing amplifier An op-amp circuit whose output is proportional to the sum of its instantaneous voltages.

Superconductor Metal such as lead or niobium that, when cooled to within a few degrees of absolute zero, can conduct current with no resistance.

Super heterodyne receiver Radio receiver that converts all radio frequencies to a fixed intermediate frequency to maximise gain and bandwidth before demodulation.

Superposition theorem Theorem designed to simplify networks containing two or more sources. It states that in a network containing more than one source, the current at any one point is equal to the algebraic sum of the currents produced by each source acting separately.

Thevenin’s theorem Theorem that replaces any complex network with a single voltage source in series with a single resistance.

Threshold Minimum point at which an effect is produced or detected.

Threshold voltage For an enhancement MOSFET, the minimum gate source voltage required for conduction of source drain current.

Thyristor A term used to classify all four layer semiconductor devices. Scrs and triacs are examples of thyristors.

Time Division Multiplexing (TDM) Transmission of two or more signals on the same path, but at different times.

Transformer Inductor with two or more windings. Through mutual inductance, current in one winding called a primary will induce current into the other windings called secondaries.

Transistor Term derived from transfer resistor. Semiconductor device that can be used as an amplifier or as an electronic switch.

Triac Bidirectional gate controlled thyristor similar to an SCR, but capable of conducting in both directions. Provides full wave control of AC power.

Triangular wave A repeating wave that has equal positive going and negative going ramps. The ramps have linear rates of change with time.

Trivalent element One having three valence electrons. Used as an impurity in semiconductor material to produce p-type material. Most commonly used trivalent elements are: Aluminum, Gallium and Boron.

Tunnel diode Heavily doped junction diode that has negative resistance in the forward direction of its operating range.

Unijunction transistor Three terminal device that acts as a diode with its own internal voltage divider biasing circuit.

Valence shell The outermost electron shell for a given atom. The number of electrons in this shell determines the conductivity of the atom.

Varactor diode p-n junction diode with a high junction capacitance when reverse biased. Most often used as a voltage controlled capacitor. The varactor is also called: varicap, tuning diode and epicap.

Voltage Controlled Oscillator Oscillator whose output frequency depends on an input control voltage.

Wien-bridge oscillator Oscillator that uses an RC low-pass filter and an RC high-pass filter to set the frequency of oscillations.

Wheatstone bridge Four arm bridge circuit used to measure resistance, inductance or capacitance.

Wideband amplifier Also called broadband amplifier. Amplifier with a flat response over a wide range of frequencies.

Zener diode Semiconductor diode in which reverse breakdown voltage current causes the diode to develop a constant voltage. Used as a clamp for voltage regulation.