RRB JE CBT 2 - Electronics key terms

A pure semiconductor such as silicon or germanium with no added impurities, where the number of free electrons equals the number of holes and conductivity is very low at room temperature.

Deliberate addition of small amounts of trivalent or pentavalent impurity atoms to a pure semiconductor to raise its conductivity and create p-type or n-type material.

The narrow zone around a p-n junction where mobile charge carriers have diffused away, leaving fixed ionised atoms and an internal electric field that opposes further diffusion.

The built-in voltage across a forward-biased p-n junction that must be overcome before appreciable current flows; about 0.7 V for silicon and 0.3 V for germanium.

A controlled, non-destructive reverse breakdown in a heavily doped junction where the strong field releases carriers; the nearly constant breakdown voltage is used for voltage regulation.

A circuit, usually using one or more diodes, that converts alternating current into unidirectional current; half-wave, full-wave centre-tap and bridge types differ in ripple and efficiency.

The ratio of the RMS value of the alternating component of a rectifier output to its DC component, indicating how smooth the output is; smaller values mean better filtering.

Setting the quiescent DC operating point of a transistor with resistors and supply voltages so that the device stays in the active region for the whole signal swing.

Returning a fraction of the output signal to the input in phase opposition, which reduces gain but improves bandwidth, stability, distortion and input/output impedance characteristics.

For an operational amplifier, the frequency at which the open-loop gain falls to unity; it stays roughly constant, so closed-loop gain and bandwidth trade off.

A node at the inverting input of an ideal op-amp in negative feedback that sits at almost the same potential as the non-inverting input without being physically grounded.

A mathematical system of binary variables and logic operations AND, OR and NOT, with laws such as De Morgan's theorems used to simplify and design digital circuits.

A grid arrangement of minterms in Gray-code order that allows visual grouping of adjacent 1s to obtain a minimal sum-of-products or product-of-sums logic expression.

A bistable sequential logic element that stores one bit and changes state on a clock edge or control input; common types are SR, JK, D and T.

A chain of flip-flops that moves stored bits one position per clock pulse, used for serial-to-parallel conversion, delay lines and data storage.

A combinational circuit that selects one of several data inputs and routes it to a single output, controlled by select lines; also called a data selector.

A modulation scheme in which the amplitude of a high-frequency carrier is varied in proportion to the instantaneous amplitude of the message signal while frequency and phase stay fixed.

For amplitude modulation, the ratio of message amplitude to carrier amplitude; values above one cause overmodulation and envelope distortion.

A scheme in which the instantaneous frequency of the carrier deviates according to the message signal amplitude, giving constant carrier amplitude and better noise immunity than AM.

A band-limited signal must be sampled at least twice its highest frequency component to be reconstructed without aliasing, setting the basis for PCM and digital transmission.

A digital encoding method that samples an analog signal, quantises each sample to discrete levels and codes it as a binary word for transmission or storage.

The sequence of fetch, decode and execute steps by which a processor reads an instruction from memory, interprets it and carries out the required operation.

A register holding the address of the next instruction to be fetched; it is automatically incremented after each fetch and altered by jumps and calls.

The rule that specifies how an instruction locates its operand, for example immediate, direct, register, register-indirect or indexed addressing.

Any linear two-terminal network can be replaced by an equivalent voltage source in series with a resistance, found from the open-circuit voltage and the equivalent resistance.

Any linear two-terminal network can be replaced by an equivalent current source in parallel with a resistance, equal to the short-circuit current and the equivalent resistance.

A source delivers maximum power to a load when the load resistance equals the source's internal or Thevenin resistance, giving an efficiency of fifty percent.

The condition in an RLC circuit where inductive and capacitive reactances cancel, making impedance purely resistive and current or voltage reach a maximum or minimum.

A measurement instrument that plots signal voltage against time on a phosphor screen, allowing observation of waveform shape, amplitude, frequency and phase.

A four-arm resistance network balanced when the ratio of adjacent arms is equal, used to measure unknown resistance precisely with a galvanometer as the null detector.

Error caused when a measuring instrument draws current from the circuit under test and alters the very voltage or current it is meant to measure.

A four-layer latching semiconductor switch that conducts only after a gate pulse and forward voltage, then stays on until current falls below the holding value.

A method of regulating power delivered to a load by delaying the firing angle of a thyristor or triac within each AC half-cycle.

A program that translates an entire high-level source program into machine code before execution, reporting syntax errors and producing a separate executable file.

A finite, ordered set of unambiguous steps that transforms given inputs into a desired output and always terminates.

The process of expressing a value in another base, such as binary, octal, decimal or hexadecimal, by repeated division or weighted positional expansion.

A form of deductive reasoning with two premises and a conclusion, tested in reasoning sections by checking whether the conclusion necessarily follows.

A reasoning task in which the pattern of a number, letter or figure sequence must be identified to determine the next or missing element.