Karnataka II PUC Electronics (KSEAB) key terms

A pure semiconductor crystal with no added impurities, in which the number of free electrons equals the number of holes. Its conductivity is low and rises with temperature because thermal energy creates more electron-hole pairs.

A semiconductor deliberately doped with donor or acceptor impurities to raise its conductivity. It becomes n-type when donors supply extra electrons and p-type when acceptors supply extra holes as the majority carriers.

The energy difference between the top of the valence band and the bottom of the conduction band. The gap sets how easily electrons are freed, roughly 1.1 eV for silicon and 0.7 eV for germanium.

The narrow zone on each side of a p-n junction where mobile carriers have diffused away, leaving fixed ionised atoms. It contains no free carriers and creates a built-in potential barrier opposing further diffusion.

A two-terminal device formed by a p-n junction that conducts readily in forward bias and blocks current in reverse bias. Its arrow-shaped symbol marks the anode and cathode and indicates the permitted conventional current direction.

A heavily doped diode designed to operate in reverse breakdown, where the voltage across it stays nearly constant over a wide current range. It is used to provide a stable reference or regulate voltage.

A circuit that converts alternating current into unidirectional current. Half-wave rectifiers use one diode, full-wave types use a centre-tapped or bridge arrangement, and filtering smooths the resulting ripple.

The ratio of the alternating component of a rectifier's output to its direct component, expressed as a measure of residual hum. A smaller value means a smoother output approaching pure direct current.

A large capacitor connected across a rectifier's output that charges on each peak and discharges into the load between peaks. It reduces ripple and raises the average output voltage.

A circuit that holds the output voltage constant despite changes in input voltage or load current. It may use a Zener diode alone or a series transistor with feedback, and is often supplied by an integrated regulator chip.

A three-terminal device with emitter, base and collector made of two p-n junctions. A small base current controls a much larger collector current, giving the transistor current amplification and switching action.

The ratio of collector current to base current in a bipolar transistor in the common-emitter connection. Typical values are tens to hundreds, and beta depends on collector current, temperature and device type.

Setting the steady direct currents and voltages at a transistor's terminals so it sits in the desired region of its characteristic curves. Proper bias keeps the device in the active region for amplification.

The steady collector current and collector-emitter voltage a transistor holds with no signal applied, also called the quiescent point. Its position on the load line determines how much output swing is possible without clipping.

A straight line drawn on the output characteristic curves showing all collector current and voltage pairs permitted by the external supply and load resistor. The operating point must lie on this line.

A voltage-controlled three-terminal device in which an electric field at the insulated gate modulates the conductivity of a channel between source and drain. It draws almost no gate current and has very high input resistance.

The ratio of change in drain current to the change in gate-source voltage that causes it, measured in siemens. It expresses how strongly the gate controls drain current in a field-effect transistor.

A transistor amplifier stage with the emitter shared between input and output, giving voltage gain and current gain with the output inverted. It is the most widely used configuration because of its high gain.

The ratio of the alternating output voltage to the input voltage of an amplifier stage, usually quoted as a number or in decibels. It depends on the device parameters, load and biasing.

Returning a fraction of an amplifier's output to its input in phase opposition to the input signal. It reduces gain but improves stability, bandwidth, linearity and input or output impedance as required.

A logarithmic unit for expressing the ratio of two powers or voltages. For power it is ten times the logarithm of the ratio; for voltage or current it is twenty times the logarithm of the ratio.

The range of frequencies over which an amplifier's gain stays within a stated limit, usually three decibels below its mid-frequency value. It is the difference between the upper and lower cut-off frequencies.

A circuit that generates a sustained alternating output without an external input signal. It needs positive feedback and a frequency-determining network such as an inductor-capacitor tank or resistor-capacitor network.

The condition for sustained oscillation: the loop gain around the feedback path must equal one in magnitude and the total phase shift must be a whole multiple of 360 degrees. It sets the required amplifier gain and feedback fraction.

A two-state circuit whose transistors switch alternately between saturation and cut-off. Depending on coupling it is astable, generating pulses; monostable, giving one timed output per trigger; or bistable, latching until retriggered.

A high-gain direct-coupled differential amplifier supplied as an integrated circuit with two inputs and one output. External components set its gain and function, and it has very high input and very low output impedance.

The condition in a negative-feedback operational amplifier circuit where the inverting input sits at almost the same potential as the earthed non-inverting input, though no direct connection exists. It simplifies gain calculations.

A circuit, usually an operational amplifier used without feedback, that compares an input voltage with a reference and swings its output to one extreme or the other. It is used for zero-crossing detection and level sensing.

A basic digital circuit that produces an output determined by the combination of its binary inputs. AND, OR, NOT, NAND, NOR and exclusive-OR gates are the building blocks of combinational circuits.

A table listing every possible combination of inputs to a logic circuit alongside the required output for each. It completely defines the behaviour of a gate or combinational circuit.

The branch of algebra using variables that take only the values zero and one, with AND, OR and NOT operations. Its identities are used to simplify logic expressions before implementing them.

A rectangular grid in which adjacent cells differ in only one input variable, used to simplify Boolean expressions graphically. Grouping neighbouring ones eliminates redundant terms and yields a minimal expression.

A bistable digital storage element with two stable output states that retains its value until a clock or input signal changes it. It forms the basis of registers, counters and memory.

The process of varying a property of a high-frequency carrier wave in step with a lower-frequency information signal. Amplitude, frequency and phase modulation are the common forms in analogue communication.

A number describing how strongly a carrier is varied by the modulating signal. In amplitude modulation it is the ratio of modulating amplitude to carrier amplitude; values above one cause overmodulation and distortion.

The process of recovering the original information signal from a modulated carrier at the receiver. It reverses modulation and is followed by amplification and filtering before the signal reaches the output device.

A conductor structure that radiates a guided electrical signal into space as electromagnetic waves, or intercepts such waves and converts them back into a signal. Its length is usually related to the wavelength used.

A component that converts electrical energy into light or light into electrical energy, such as a light-emitting diode, photodiode or solar cell. Operation depends on electrons crossing the energy band gap.

A forward-biased semiconductor junction that emits light when electrons and holes recombine across the band gap. The colour depends on the semiconductor material and hence on the gap energy.

A reverse-biased p-n junction whose reverse current increases in proportion to the light falling on it. It is used for light detection and in optical communication receivers.

A four-layer thyristor that blocks current in both directions until a gate pulse triggers it into conduction, after which it latches on until current falls below the holding value. It is used for power control.

A measuring instrument that displays how a signal voltage varies with time on a fluorescent screen. Vertical and horizontal controls set voltage and time scales, allowing amplitude, period and phase to be read.

A general-purpose instrument that measures voltage, current and resistance, often with additional ranges for continuity, capacitance or transistor testing. Digital types display numeric values; analogue types use a moving pointer.

A laboratory instrument producing alternating voltages of adjustable frequency, amplitude and waveform, commonly sine, square and triangular. It supplies test signals to circuits under measurement.

The reverse voltage at which a Zener diode enters breakdown and begins to hold its voltage nearly constant. It is specified at a particular test current and drifts slightly with temperature and current.