Electronic Engineering Dictionary

UDIMM. UnBuffered DIMM [Dual In-Line Memory Module]. A type of DIMM memory stick; the front side PWB pins are not connected to the rear side pins, pins used for different functions. Also refer to Definitions of Memory Modules.

UJT. Uni-Junction Transistor. A three-terminal semiconductor device having one junction and a stable negative-resistance characteristic over a wide temperature range. [Transistor Manufacturers]

u-LAW. A companding algorithm used in digital communications to reduce the dynamic range of an audio signal. Refer to the telcom section for u-Law IC Functions.

ULP. Upper Level Protocol. The protocol which runs on top of Fibre Channel through the FC-4 layer. Typical ULPs running over Fibre Channel are Small Computer System Interface (SCSI), Internet Protocol (IP), High Performance Parallel Interface (HIPPI), and Intelligent Peripheral Interface (IPI).

Ultrahigh Frequency. [UHF] The band of frequencies from 300 megahertz to 3 gigahertz.

Ultrasonic. Sounds above 20,000 hertz. Supersonic.

UMOS. A type of MOS [Metal-Oxide-Semiconductor] FET [Field Effect Transistor]. Refer to FET Manufacturers.

Unbalanced Attenuator. An attenuator which has the resistance elements in one side of the line, with the other line normally used as a ground return [3 types shown in the schematic to the right].

Unbalanced Crystal Mixer. A circuit consisting of a section of coaxial transmission line one-half wavelength long that is tuned to the difference (intermediate) frequency between the local oscillator and RF echo signals.

Unbalanced Line. A transmission line, such as a coaxial cable, in which the magnitudes of the voltages on the two conductors are not equal with respect to ground.

Uncertainty. An expression of the combined errors in a test measurement process.

Underdamped. The attempt at smoothing out oscillations that does not prevent oscillations. Graphic of an Underdamped oscillation.

Underflow. In computing, a condition occurring when a machine calculation produces a non-zero result that is smaller than the smallest non-zero quantity that the machines storage unit is capable of storing or representing.

Underground Cable. A buried cable used for communication or power distribution; refer to the graphic to the right.

Undershoot. See Definitions of Pulse Characteristics.

Unencased. Having no enclosure. Not residing within an enclosure.

Unidirectional. In one direction only.

Uniform Transmission Line: A transmission line that has distributed electrical properties, i.e., resistance, inductance, and capacitance per unit length, that are constant along the line, and in which the voltage-to current ratio does not vary with distance along the line, if the line is terminated in its characteristic impedance.

Unijunction Transistor. [UJT] A three-terminal, semiconductor device with a negative resistance characteristic that is used in switching circuits, oscillators, and wave-shaping circuits. The leads are Anode, Gate, and Cathode.

UJT Symbol

Uninterruptible Power Supply. A device that is inserted between a primary power source, such as a commercial utility, and the primary power input of equipment to be protected, e.g., a computer system, for the purpose of eliminating the effects of transient anomalies or temporary outages. (UPS vendors).

Unipolar. An active solid-state device in which only one type of charge carrier, positive or negative, is used to support current flow.

Unipolar Transistor. A FET. A transistor in which the source to drain current involves only one type of charge carrier.

Unipolar Signal. A two-state signal where one of the states is represented by voltage or current and the other state is represented by no voltage or current.

Unit. An assembly or any combination of parts, subassemblies, and assemblies mounted together. Normally capable of independent operation. A single object or thing.

Unit Impulse. A mathematical artifice consisting of an impulse of infinite amplitude and zero width, and having an area of unity.

Unit Size. The standards adopted to make comparisons between things of like value (for example, the unit size for conductors is the mil-foot).

Unity Coupling. A condition when 100 percent of the magnetic field of an inductor couples energy to another inductor.

Unity Gain. A gain of one. An amplifier that appears like a buffer. The graphic shows an Op-Amp configured as a Unity Gain amplifier. Note RL and CL are not required, but are shown to represent the load.

OpAmp Setup for Unity Gain

Universal Motor. A motor which is designed for operation from either a single phase alternating current or direct current source.

Universal Output Transformer. A transformer with a large number of taps on both the primary and secondary windings so that a number of different input and output impedances or voltages may be selected or produced.

Universal Time Constant Chart. A chart used to find the time constant of a circuit if the impressed voltage and the values of R and C or R and L are known. [Time Constant Chart]

Untapped Delay Line. A simple fixed circuit delay with out adjustment or programmability. Related terms; Tapped Delay Line, Programmable Delay Line

Untapped Delay Line

Untuned Line. Another name for the flat or non-resonant line.

Up-Converter. A device that translates frequencies from lower to higher frequencies.

Up-Down Counter. A counter that can either count up or count down as in a 74192 IC Counter

Up Link. The frequency used to transmit a signal from earth to a satellite.

Upper Frequency Cutoff. The highest frequency a circuit can pass.

Upper Sideband. All of the sum frequencies above the carrier.

USB. Universal Serial Bus, a computer bus which provides two-way communication between the PC and peripheral devices, over a differential 4-wire serial interface cable. Refer to USB type A and B connectors to the right.

Useful Life. The second phase of the lifetime of a population of a particular component when only random failures occur.

UTOPIA Bus. A Bus Standard used as the Test and Operations Physical Interface for ATM [Asynchronous Transfer Mode] standard.

UV. Ultra-Violet light. Refer to a Graph of the UV Spectrum.

UV Erasable. A term which describes how EPROMs or other memory devices might be erased or reset.

UXGA. Ultra Extended Graphics Array. A video resolution of 1600 x 1200 pixels. [PC Video Monitor Buses]