[align=left]source
Device that provides signal power or energy to a load.
source follower
FET amplifier in which signal is applied between gate and drain with output taken between source and drain. Also called "common drain."
source impedance
Impedance through which output current is taken from a source.
south pole
Pole of a magnet into which magnetic lines of force are assumed to enter.
spark
Momentary discharge of electrical energy due to ionization of air or other dielectric material separating two charges.
SPDT
Single pole double throw.
speaker
Also called "loudspeaker." Transducer that converts electrical energy into mechanical energy at audio frequencies.
spectrum
Arrangement or display of light or other forms of electromagnetic radiation separated according to wavelength, energy or some other property.
spectrum analyzer
Instrument used to display the frequency domain of a waveform plotting amplitude against frequency.
speed-up capacitor
Capacitor added to the base circuit of a BJT switching circuit to improve the switching time of the device.
SPST
Abbreviation for "single pole single throw."
square wave
Wave that alternates between two fixed values for an equal amount of time.
static electricity
Stationary electric charges.
static reverse current
Reverse current through a zener diode when the reverse voltage across the diode is less than the zener voltage rating of the device.
stator
Stationary part of some rotary device such as a variable capacitor.
step-down transformer
Transformer in which the output AC voltage is less than the input AC voltage.
step-up transformer
Transformer in which the output AC voltage is greater than the input AC voltage.
stereo sound
System in which reproduced sound is delivered through two or more channels to give a sense of direction to the source.
stop band
Range of frequencies outside the pass band of a tuned amplifier.
storage time
In a BJT switching circuit, it is the time required for collector current to drop from 100% to 90% of its maximum value.
stranded conductor
Conductor composed of a group of strands of wire twisted together.
stray capacitance
Undesirable capacitance that exists between two conductors such as two leads or one lead and a ****l chassis.
subassembly
Components contained in a unit for convenience in assembling or servicing equipment.
subatomic
Particles such as electrons, protons and neutrons that are smaller than atoms.
substrate
Mechanical insulating support upon which a device is fabricated.
summing amplifier
An op-amp circuit whose output is proportional to the sum of its instantaneous voltages.
superconductor
****l such as lead or niobium that, when cooled to within a few degrees of absolute zero, can conduct current with no resistance.
super heterodyne receiver
Radio receiver that converts all radio frequencies to a fixed intermediate frequency to maximize gain and bandwidth before demodulation.
super high frequency
(SHF) Frequency band between 3 GHz and 30 GHz. So designated by Federal Communications Commission (FCC).
superposition theorem
Theorem designed to simplify networks containing two or more sources. It states that in a network containing more than one source, the current at any one point is equal to the algebraic sum of the currents produced by each source acting separately.
supply voltage
Voltage provided by a power source.
surface leakage current
Diode reverse current that passes along the surface of the semiconductor materials.
surge current
High charging current that flows into a power supply filter capacitor as the power is first turned on.
sweep generator
Test instrument designed to produce a voltage that continuously varies in frequency over a band of frequencies. Used as a source to display frequency response of a circuit on an oscilloscope.
switch
Electrical device having two states, on (closed) or off (open). Ideally having zero impedance when closed and infinite impedance when open.
switching transistor
transistor designed to change rapidly between saturation and cut-off.
synchronization
Also called sync. Precise matching of two waves or functions.
synchronous
Two or more signals in step or in phase.
sync pulse
Pulse used as a reference for synchronization.
system
Combination of several pieces of equipment to perform in a particular manner.
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T
tank circuit
Parallel resonant circuit containing only a coil and a capacitor. Both the coil and capacitor store electrical energy for part of each cycle.
tantalum capacitor
Electrolytic capacitor having a tantalum foil anode. Able to have a large capacity in a small package.
tap
Electrical connection to some point other than at the ends of a resistor or inductor.
tapered
Nonunifrom distribution of resistance per unit length throughout the element of a potentiometer.
telegraphy
Communication between two points by sending and receiving a series of current pulses either through wire or by radio.
telemetry
Transmission of instrument readings to a remote ******** either by wire or by radio.
telephone
Apparatus designed to convert sound waves into electrical waves which are sent to and reproduced data distant point.
telephone line
Wires existing between subscribers and central stations in a telephone system.
telephony
Telecommunications system involving the transmission of speech information, allowing two or more persons to communicate verbally.
television
System that converts both audio and visual information into corresponding electrical signals which are then transmitted through wires or by radio waves to a receiver which reproduces the original information.
telex
Teletypewriter exchange service.
temperature coefficient of frequency
Rate at which frequency changes with temperature.
tera
(T) Metric prefix that represents 1012.
terminal
Point at which electrical connections are made.
tesla
(T) Unit of magnetic flux density. (1 tesla = 1 Wb/m2).
test
Sequence of operations intended to verify the correct operation or malfunctioning of a piece of equipment or system.
thermal relay
Relay activated by a heating element.
thermal runaway
Problem that can develop in an amplifier when an increase in temperature causes an increase in collector current. The increase in collector current causes a further increase in temperature and so on. Unless the circuit is designed to prevent this condition, the device can be driven into saturation.
thermal stability
The ability of a circuit to maintain stable characteristics in spite of increased temperature.
thermistor
Temperature sensitive semiconductor that has a negative temperature coefficient of resistance. As temperature increases, resistance decreases.
thermocouple
Temperature transducer consisting of two dissimilar ****ls welded together at one end to form a junction that when heated will generate a voltage.
thermometry
Relating to the measuring of temperature.
thermostat
Device that opens or closes a circuit in response to changes in temperature.
Thevenin’s theorem
Theorem that replaces any complex network with a single voltage source in series with a single resistance.
thick-film capacitor
Capacitor consisting of two thick-film layers of conductive film separated by a deposited thick-layer dielectric film.
thick film resistor
Fixed value resistor consisting of thick-film resistive element made from ****l particles and glass powder.
thin film capacitor
Capacitor in which both the electrodes and the dielectric are deposited in layers on a substrate.
thin film detector
(TFD) A temperature detector containing a thin layer of platinum and used for precise temperature readings.
three phase supply
AC supply that consists of three AC voltages 120° out of phase with each other.
threshold
Minimum point at which an effect is produced or detected.
threshold voltage
For an enhancement MOSFET, the minimum gate source voltage required for conduction of source drain current.
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