saturation - Condition in which a further increase in one variable produces no further increase in the resultant effect. In a bipolar junction transistor, the condition when the emitter to collector voltage is less than the emitter to base voltage. This condition puts forward bias on the base to collector junction.
sawtooth wave - Repeating waveform that rises from zero to maximum value linearly drops back to zero and repeats. A ramp waveform.
scale - Set of markings used for measurement.
schematic diagram - Illustration of an electrical or electronic circuit with the components represented by their symbols.
Schmitt trigger - Circuit to convert a given waveform to a square wave output.
Schottky diode - High speed diode that has very little junction capacitance. Also known as a "hot-carrier diode" or a "surface-barrier diode."
scientific notation - Numbers entered as a number from one to ten multiplied by a power of ten. Example: 8765 = 8.765 × 103.
secondary - Output winding of a transformer. Winding that is connected to a load.
secondary cell - Electrolytic cell used to store electricity. Once discharged may be restored by recharging by putting current through the cell in the direction opposite to that of discharge current.
selectivity - Characteristic of a circuit to discriminate between wanted and unwanted signals.
self biasing - Gate bias for a field effect transistor in which source current through a resistor produces the voltage for gate to source bias.
self inductance - Property that causes a counter electromotive force to be produced in a conductor when the magnetic field expands or collapses with a change of current.
semiconductor - An element which is neither a good conductor or a good insulator, but rather lies somewhere between the two. Characterized by a valence shell containing four electrons. Silicon, germanium and carbon are the semiconductors most frequently used in electronics.
series circuit - Circuit in which the components are connected end to end so that current has only one path to follow through the circuit.
series parallel network - Network that contains components connected in both series and parallel.
series resonance - Condition that occurs in a series LC circuit at the frequency where inductive reactance equals capacitive reactance. Impedance is minimum, current is maximum limited only by resistance in the circuit.
seven segment display - Device made of several light emitting diodes arranged in a numeric or alphanumeric pattern. By lighting selected segments numeric or alphabet characters can be displayed.
shells or bands - Orbital path containing a group of electrons having a common energy level.
shield - Metal grounded cover used to protect a wire, component or piece of equipment from stray magnetic and/or electric fields.
short circuit - Also called a short. Low resistance connection between two points in a circuit typically causing excessive current.
shunt resistor - Resistor connected in parallel or in shunt with another component or circuit.
signal - Electrical quantity that conveys information.
signal to noise ratio - Ratio of the magnitude of the signal to the magnitude of noise usually expressed in decibels.
silicon - (Si) Non metallic element (atomic number 14) used in pure form as a semiconductor.
silicon-controlled rectifier - (SCR) Three terminal active device that acts as a gated diode. The gate terminal is used to turn the device on allowing current to pass from cathode to anode.
silicon controlled switch - An SCR with an added terminal called an anode gate. A positive pulse either at the anode gate or the cathode gate will turn the device on.
silicon dioxide - Glass like material used as the gate insulating material in a MOSFET.
silicon transistor - A bipolar junction transistor using silicon as the semi conducting material.
silver - (Ag) Precious metal that does not easily corrode and is more conductive than copper.
silver mica capacitor - Mica capacitor with silver deposited directly onto the mica sheets instead of using conductive metal foil.
silver solder - Solder composed of silver, copper and zinc. Has a melting point lower than pure silver, but higher than lead-tin solder.
simplex - Communication in only one direction at a time. Example: FAX.
simulcast - Broadcasting a program simultaneously in two different forms, for example a program broadcast in both AM and FM.
sine - Sine of an angle of a right angle triangle is equal to the opposite side divided by the hypotenuse.
sine wave - Wave whose amplitude is the sine of a linear function of time. It is plotted on a graph that plots amplitude against time or radial degrees relative to the angular rotation of an alternator.
single in-line package - Package containing several electronic components (generally resistors) with a single row of connecting pins.
single pole double throw - (SPDT) Three terminal switch in which one terminal can be connected to either one of the other terminals.
single pole single throw - (SPST) Two terminal switch or relay that can open or close one circuit.
single sideband - (SSB) AM radio communication technique in which the transmitter suppresses one sideband and therefore transmits only a single sideband.
single throw switch - Switch containing only one set of contacts which can be either opened or closed.
sink - Device such as a load that consumes power or conducts away heat.
sintering - Process of bonding either a metal or powder by cold pressing it into a desired shape and then heating to form a strong cohesive body.
sinusoidal - Varying in proportion to the sine of an angle or time function. AC voltage in which the instantaneous value is equal to the sine of the phase angle times the peak value.
SIP - Abbreviation for "single in-line package."
skin effect - Tendency of high-frequency (rf) currents to flow near the surface layer of a conductor.
slew rate - The maximum rate at which the output voltage of an op-amp can change.
slide switch - Switch having a sliding button, bar or knob.
slow acting relay - Slow operating relay that when energized may not pull up the armature for several seconds.
slow-blow fuse - Fust that can withstand a heavy current (up to ten times its rated value) for a small period of time before it opens.
snap switch - Switch containing a spring under tension or compression that causes the contacts to come together suddenly when activated.
SNR - Abbreviation for "signal to noise ratio."
soft magnetic material - Ferromagnetic material that is easily demagnetized.
software - Program of instructions that directs the operation of a computer.
solar cell - Photovoltaic cell that converts light into electric energy. Especially useful as a power source for space vehicles.
solder - Metallic alloy used to join two metal surfaces.
soldering - Process of joining two metallic surfaces to make an electrical contact by melting solder (usually tin and lead) across them.
soldering iron - Tool with an internal heating element used to heat surfaces being soldered to the point where the solder becomes molten.
solenoid - An air core coil. Equipped with a movable iron core the solenoid will produce motion. As a result of current through the coil the iron core is pulled into the center of the winding. When the coil is deenergized, a spring pulls the movable core away from the center of the winding. Mechanical devices connected to the movable core are made to move as a result of current through the coil. Example: Electric door locks on some automobiles.
solid conductor - Conductor having a single solid wire instead of strands of fine wire twisted together.
solid state - Pertaining to circuits where signals pass through solid semiconductor material such as transistors and diodes as opposed to vacuum tubes where signals pass through a vacuum.
sonar - Acronym for "sound navigation and ranging." A system using reflected sound waves to determine the position of some target.
sonic - Pertaining to sound.
sound wave - Pressure waves propagated through air or other plastic media. Sound waves are generally audible to the human ear if the frequency is between approximately 20 and 20,000 vibrations per second. (hertz)
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 - Crackling noise heard on AM radio receivers. Caused by electric storms or electric devices.
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 metal 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 - Metal 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-barrier diode - (Schottky diode) High speed diode that has very little junction capacitance. Also known as a "hot-carrier diode."
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.