Electronic Engineering Glossary Terms

Logic. The basic principles and applications of truth tables, interconnections of off-on circuit elements, and other factors involved in mathematical computation in automatic data processing systems and other devices.

Logical Block Addressing. [LBA] The LBA is the address that the operating system uses to read or write a block of data on the flash drive. A common scheme used for specifying the location of blocks of data stored on computer storage devices.

Logic Analyzer. A piece of electronic equipment that displays signals as logic waveforms, either high or low by sampling the signal at high speed. Also see companies making Logic Analyzers

Logic Circuit. The primary control information processor in digital equipment; made up of electronic gates and so named because their operation is described by simple equations of a specialized logic algebra.

Logic Diagram. In computers and data processing equipment, a diagram representing the logical elements and their interconnections without necessarily expressing construction or engineering details.

Logic Element. The smallest building blocks that can be represented by operators in an appropriate system of symbolic logic. Typical logic elements are the AND-gate and the flip-flop, which can be represented as operators in a suitable symbolic logic. Also a device that performs the logic function.

Logic Instruction. Any instruction that executes a logic operation that is defined in symbolic logic, such as AND, OR, NAND, or NOR.

Logic Operation. A non-arithmetical operation in a computer, such as comparing, selecting, making references, matching, sorting, and merging, where the logical YES or NO quantities are involved.

Logic Switch. A semiconductor switch. A switch that changes positions based on the logical combinations of an input. A diode matrix or other switching arrangement that is capable of directing an input signal to one of several outputs.

Logic Symbol. A symbol used to represent a logic element graphically. Also a symbol used to represent a logic operator.

Longitudinal Balance. The electrical symmetry, with respect to ground, of the two wires of a pair.

Longitudinal Voltage. See Common-Mode Voltage.

Longitudinal Waves. Those waves in which the disturbance (back and forth motion) takes place in the direction of propagation. Sometimes called compression waves.

Long-tailed Pair. A common emitter resistor connected off two emitter coupled transistors. The bias resistor [Re] acts as a constant current source. The resistor is the 'tail' hanging of the transistor pair. A long tail is a larger resistor which more closely resembles a constant current source.

Long-Term Stability. The degree of uniformity of oscillator frequency over time, when the frequency is measured under identical environmental conditions, such as supply voltage, load, and temperature.

Loop. A curved conductor that connects the ends of a coaxial cable or other transmission line and projects into a waveguide or resonant cavity for the purpose of injecting or extracting energy. A communications channel from a switching center or an individual message distribution point to the user terminal.

Loop-Back. A method of performing transmission tests. A receiver that returns the transmitted data back to the transmitter that just sent it.

Looped Dual Bus. A distributed-queue dual-bus (DQDB) scheme in which the head-of-bus functions for both buses are at the same location.

Loop Filter. In a phase-locked loop, a filter located between the phase detector (or time discriminator) and the voltage controlled oscillator (or phase shifter).

Loop Gain. The sum of the gains, expressed in dB, acting on a signal passing around a closed path, i.e., a loop.

Loose Coupling. Inefficient coupling of energy from one circuit to another that is desirable in some applications. Also called weak coupling.

Loss. The signal reduction due to attenuation. The loss of a signal. The diminution, usually expressed in dB, of signal level in a communications medium.

Loss Factor. The ratio of average power to peak power dissipated in a line or load.

Lossy Line. A transmission line with a high amount of attenuation per unit length.

Loudness Control. An audio control that combines a tone control and a volume control. Also refer to Loudness Adjustment Circuit Diagram.

Loudspeaker. See speaker. An item designed to convert audio frequency electrical energy into acoustic energy which it projects over a distance.

Lower-Frequency Cutoff. The lowest frequency a circuit will pass.

Lower Sideband. All difference frequencies below that of the carrier.

Lowest Replaceable Unit. [LRU] An LRU is the lowest possible unit to be replaced within the system component during site level maintenance activities. It is a separate, installable physical package performing a single function or group of closely related functions.

Lowest Usable Frequency. The minimum operating frequency that can be used for communications between two points.

Low Frequency. The band of frequencies from 30 kHz to 300 kHz.

Low Frequency Compensation. Compensation added to a circuit or amplifier when used in low frequency applications. The compensation could take the form of additional components or value changes to capacitors to overcome the distortion caused by capacitance reactance and allow the circuit to function at a low frequency [or lower frequency].

Low Frequency Distortion. Frequency distortion which effects lower frequencies. Distortion

Low Level Modulation. Modulation produced in an earlier stage than the final.

Low Noise Amplifier. See Preamplifier. An amplifier whose noise temperature is low.

Low-Pass Filter. A filter that passes a majority of the low frequencies on to the next circuit and rejects, or attenuates, the higher frequencies. Also called a high-frequency discriminator. Refer to the entry on Passive Filters, or refer to an Active Low Pass Filter Circuit, which uses an Op Amp. A filter network that passes all frequencies below a specified frequency with little or no loss, but strongly attenuates higher frequencies. A via in a Printed Circuit Board [PCB] also acts as a low pass filter. Related definitions; PCB Definitions.

L-pad. An attenuation pad composed of two discrete components, one series component and one shunt component, forming an 'L'.

Low Power FM Radio. [LPFM] A broadcast service that permits the licensing of 50-100 watt FM radio stations within a service radius of up to 3.5 miles and 1-10 watt FM radio stations within a service radius of 1 to 2 miles.

Low Side Drive. A component or IC designed to be placed within a circuit between the load and ground, so the driver switches the load into the circuit on the low side [nearest to ground].

Lumped Constants. The properties of inductance, capacitance, and resistance in a transmission line. The single electrical equivalent of the properties of a circuit.

Lumped Impedance Tuning. The insertion of an inductor or capacitor in series with an antenna to electrically lengthen or shorten the antenna.