- UHF
Abbreviation for "ultra high frequency.
- ultrasonic
- Signals that are just above the frequency range of human
hearing of approximately 20 kHz.
- uncharged
- Material having atoms with the same number of electrons in
orbit as the number of protons in the nucleus. Having no electrical
charge.
- unijunction transistor
- Three terminal device that acts as a diode with its own
internal voltage divider biasing circuit.
- unity gain frequency
- Frequency of operation for a device where the gain of the
component drops to unity.
V
- VA
- Abbreviation for "volt ampere"
- vacuum tube
- Electron tube evacuated to such a degree that its electrical
characteristics are essentially unaffected by the presence of residual
gas or vapor. Have been essentially replaced by transistors for
amplification and rectification. Cathode ray tubes are still used as
display devices.
- valence shell
- The outermost electron shell for a given atom. The number of
electrons in this shell determines the conductivity of the atom.
- varactor diode
- PN junction diode with a high junction capacitance when
revers biased. Most often used as a voltage controlled capacitor. The
varactor is also called: varicap, tuning diode and epicap.
- variable capacitor
- Capacitor whose capacitance can be change by varying the
effective area of the plates or the distance between the plates.
- variable resistor
- Resistor whose resistance can be changed by turning a shaft.
See also "potentiometer and rheostat."
- VCR
- Abbreviation for "video cassette recorder."
- vector
- Quantity having both magnitude and direction. Normally
represented by a line. Length of the line indicates magnitude and
orientation indicates direction.
- vector diagram
- Arrangement of vectors showing phase relationships between
two or more AC quantities of the same frequency.
- vertical MOS
- Enhancement type MOSFET designed to handle much greater
values of drain current than standard E-MOSFET.
- very high frequency
- (VHF) Electromagnetic frequency band from 30 MHz to 300 MHz.
- very low frequency
- (VLF) Frequency band from 3 kHz to 30 kHz.
- video
- Relating to any picture or visual information. From the latin
word meaning "I see."
- video amplifier
- Amplifier having one or mare stages designed to amplify video
signals.
- virtual ground
- Point in a circuit that is always at approximately ground
potential. Often a ground for voltage, but not for current.
- voice coil
- Coil attatched to the diaphram of a moving coil loudspeaker.
The coil is moved through an air gap between magnetic pole pieces.
- voice synthesizer
- Synthesizer that can simlate speech by stringing together
phenomes.
- volt
- Unit of potential difference or electromotive force. One volt
is the potential difference needed to produce one ampere of current
through a resistance of one ohm.
- voltage
- (V) Term used to designate electrical pressure or force that
causes current to flow.
- voltage amplifier
- Amplifier designed to build up signal voltage. By design
amplifiers can have a large voltage gain or a large current gain or a
large power gain. Voltage amplifiers are designed to maximize voltage
gain often at the expense of current gain or power gain.
- voltage controlled oscillator
- Oscillator whose output frequency depends on an input control
voltage.
- voltage divider
- Fixed or variable series resistor network connected across a
voltage to obtain a desired fraction of that voltage.
- voltage divider biasing
- Biasing method used with amplifiers in which two series
resistors connected across a source. The junction of the two biasing
resistors provides correct bias voltage for the amplifier.
- voltage drop
- Voltage or difference in potential developed across a
component due to current flow.
- voltage feedback
- Feedback configuration where a portion of the output voltage
is fed back to the input of an amplifier.
- voltage follower
- Operational amplifier circuit characterized by a high input
impedance, low output impedance and unity voltage gain. Used as a buffer
between a source and a low impedance load.
- voltage gain
- Also called voltage amplification. Ratio of amplifier output
voltage to input voltage usually expressed in decibels.
- voltage multiplier
- Rectifier circuit using diodes and capacitors to produce a DC
output voltage that is some multiple of the peak value of AC input
voltage. Cost effective way of producing higher DC voltages. Voltage
doublers and voltage triplers are examples.
- voltage rating
- Maximum voltage a component can withstand without breaking
down.
- voltage regulator
- Device or circuit that maintains constant output voltage
(within certain limits) in spite of changing line voltage and/or load
current.
- voltage source
- Circuit or device that supplies voltage to a load.
- voltaic cell
- Primary cell having two unlike electrodes immersed in a
solution that chemically interacts to produce a voltage.
- volt-ampere
- Unit of apparent power in an AC circuit containing capacitive
or inductive reactance. Apparent power is the product of source voltage
and current.
- voltmeter
- Instrument used to measure difference in potential between
two points.
- volume
- Magnitude or power level of audio frequency. Measured in
volume units (VU).
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