UGC NET Electronic Science key terms

A pure semiconductor crystal with no intentional dopant atoms, in which electron-hole pairs are generated only by thermal excitation, so electron and hole concentrations are equal and conductivity rises steeply with temperature.

A semiconductor deliberately doped with donor or acceptor impurities so that one carrier type dominates, making its conductivity controlled by dopant concentration rather than by temperature alone.

The electrochemical potential of electrons in a solid; at absolute zero it separates occupied from empty states, and in doped semiconductors its position relative to the bands indicates whether the material is n-type or p-type.

The zone around a p-n junction where mobile carriers have diffused away, leaving uncovered ionised acceptors and donors that create a built-in electric field opposing further diffusion.

Reverse breakdown of a heavily doped junction in which the narrow depletion region allows electrons to tunnel directly between bands, giving a sharp, nearly vertical breakdown characteristic used for voltage reference diodes.

Reverse breakdown caused by impact ionisation: carriers accelerated across a wide depletion region knock out further electron-hole pairs, producing a multiplicative chain reaction that is sensitive to temperature and device structure.

The increase of collector current with collector-emitter voltage in a bipolar transistor because the base-collector depletion width grows and effectively narrows the neutral base, giving a finite output resistance.

The small-signal ratio of output current change to input voltage change at fixed output voltage; for a field-effect transistor it equals the drain current sensitivity to gate voltage and sets amplifier gain.

A linearised equivalent circuit of a nonlinear device around a chosen bias point, replacing the device with controlled sources and resistors or capacitors valid only for small excursions about that operating point.

The multiplication of an impedance connected between an amplifier's input and output by roughly one plus the gain, which greatly increases input capacitance and limits high-frequency bandwidth.

The constant product of an amplifier's closed-loop gain and its corresponding bandwidth for a given feedback configuration, marking the frequency at which open-loop gain falls to unity.

The maximum rate at which an operational amplifier output can change, usually quoted in volts per microsecond, limited by the current available to charge internal compensation capacitance.

The ratio of differential gain to common-mode gain of a differential amplifier, expressing how well it amplifies the wanted difference while suppressing a signal present on both inputs.

The condition for sustained sinusoidal oscillation in a feedback loop: the loop gain magnitude must equal unity and the total loop phase shift must be an integer multiple of 360 degrees at the oscillation frequency.

The amount by which the loop phase shift of a negative-feedback system falls short of 180 degrees at the frequency where loop gain is unity; it measures stability against oscillation.

The minimum sampling frequency, equal to twice the highest frequency present in a bandlimited signal, that allows the original signal to be reconstructed without aliasing.

The folding of high-frequency content onto lower frequencies when a signal is sampled below the Nyquist rate, producing distortion that cannot be removed by later filtering.

The error introduced when a continuous amplitude is rounded to the nearest discrete level; it behaves approximately as additive white noise whose power sets the maximum achievable signal-to-noise ratio for a given word length.

An oversampling conversion technique that shapes quantisation noise away from the signal band using a feedback loop and integrator, trading speed for high resolution at low bandwidth.

The analog low-pass filter placed after a digital-to-analog converter to remove spectral images and smooth the staircase output into a continuous bandlimited waveform.

A transform that maps a discrete-time sequence into a complex function of z, converting linear difference equations into algebraic ones and enabling stability analysis through pole locations.

The set of z-plane values for which a Z-transform sum converges; its shape and relation to the unit circle determine whether a discrete-time system is stable and causal.

A finite-length transform that maps N time samples to N frequency samples spaced evenly over one period, computable efficiently by fast algorithms and central to digital spectral analysis.

A system whose response obeys superposition and does not change with time, so it is completely characterised by its impulse response and corresponds to convolution in the time domain.

A statement that the total energy or power of a signal computed in the time domain equals that computed in the frequency domain, linking signal energy to its spectral content.

A mathematical operation combining two sequences or functions by reversing one, shifting it, multiplying and summing, giving the output of a linear time-invariant system for an arbitrary input.

The number of bit positions in which two equal-length binary words differ; it measures error patterns and determines the error-detecting and correcting capability of a code.

A linear error-correcting block code that inserts parity bits at positions that are powers of two, allowing a single-bit error to be located and corrected at the receiver.

An error-detection scheme that treats a data block as a polynomial, divides it by a generator polynomial, and appends the remainder so the receiver can verify divisibility.

The maximum error-free data rate achievable over a channel of given bandwidth and signal-to-noise ratio, forming the theoretical upper bound for any practical coding scheme.

The receive filter whose impulse response is a time-reversed copy of the known pulse shape, maximising output signal-to-noise ratio at the sampling instant in the presence of white noise.

Distortion in which energy from one transmitted symbol spreads into neighbouring symbol intervals because of limited channel bandwidth or timing error, raising the bit error rate.

The ratio of voltage to current for a single wave travelling along a uniform transmission line, determined by the line's distributed inductance and capacitance and independent of length.

The complex ratio of reflected to incident wave amplitude at a discontinuity, fixed by the load and line impedances and ranging from minus one to plus one in magnitude.

The ratio of maximum to minimum voltage magnitude along a line carrying a standing wave, indicating the degree of mismatch between load and line impedance.

A graphical aid plotting normalised impedance and admittance on a polar grid of reflection coefficients, used to solve matching and line-transformation problems without complex arithmetic.

Ratios of travelling-wave amplitudes at a network's ports, describing reflection and transmission at high frequencies where open- and short-circuit measurements are impractical.