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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. 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 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.
UNIDIRECTIONAL. In one direction only.
| 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).
UNIT. An assembly or any combination of parts, subassemblies, and assemblies mounted together. Normally capable of independent operation. A single object or thing.
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 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 |
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 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. [Universal Serial Bus]
USB Type A/B Connectors
Utopia Bus. A Bus Standard used as the Test and Operations Physical Interface for ATM [Asynchronous Transfer Mode] standard. [UTOPIA Bus]
UXGA. Ultra Extended Graphics Array. A video resolution of 1600 x 1200 pixels. [PC Video Monitor Buses]
