Electronic Engineering Dictionary

Selectivity. The ability of a receiver to select the desired signal and reject unwanted signals. The ability of a receiver to discriminate against signals using a different carrier frequency than the one that has been tuned to.

Selenium. [Se] A chemical element with light-sensitive properties that makes it useful as a semiconductor material in metallic rectifiers and photocells.

Self-Bias. In a transistor circuit, the voltage developed across a resistor connected between the collector and base [Rb in the schematic]. In a vacuum tube circuit, the voltage developed by the flow of current through a resistor in the grid or cathode leads. A bias developed by a dropping resistor rather than from a separate voltage supply. Refer to the transistor bias circuit in the side-bar.

Self-Delineating Block. A block in which a bit pattern or a flag identifies the beginning or end of a block.

Self-Excited. An oscillator that produces a build-up in output oscillations upon power up with out the need for an external input signal.

Self-Excited Generators. DC generators in which the generator output is fed to the field to produce field excitation.

Self-Excited Meter. A term used to describe meters that operate from their own power sources.

Self-Induction. The production of a counter-electromotive force in a conductor when its own magnetic field collapses or expands with a change in current in the conductor. The phenomenon caused by the expanding and collapsing fields of an electron that encircle other electrons and retard the movement of the encircled electrons.

Self-Synchronizing Code. A code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a valid code word.

Slew Rate. The rate of change a signal takes over time. How fast a signal moves from one voltage level to another voltage level over time. Read more on IC Slew Rate. In regards to ICs the voltage levels are defined so a comparison can be made between devices.

Semiconductor Die. The silicon substrate the device is etched into.

Semiconductor Junction. A region of transition between semiconductor regions of different electrical properties (n-n+, p-n, p-p+ semiconductors) or between a metal and a semiconductor.

Semiconductor Switch. A switch made using semiconductor material, normally FETs. Also called an Analog Switch.

Semiduplex Operation. Operation of a communications network in which a base station operates in a duplex mode with one or more remote stations operating in a half-duplex mode.

Semirigid Cable. A cable produced with a heavy copper outer shield. Semirigid coaxial cables are constructed of a single inner conductor covered by a flexible low-loss RF dielectric core material, which is then surrounded by a solid, continuous, metallic outer conductor. Semirigid cables may have more than one conductor. See the graphic in the lower right side-bar. Also refer to the list of Semirigid Coaxial Cable Manufacturers.

Sense Lines. One or more lines running from a power supply to the load. The Sense Lines differ from the normal power supply output lines in that they supply no current. Sense Lines are used to read the voltage level at the load and adjust the output of the supply as required to maintain the correct voltage level. Sense Lines provide an accurate voltage reading because the lines do no incur a voltage drop due to the low current drain. Generally it is recommended to interconnect sense lines directly at the connector to their respective power output terminals since sense lines in general may cause trouble. Some data sheets recommend to tie the sense line to the supply output at the unit and not run the sense lines to the load at all. If the sense lines are used twist the sense line with the ground line and run them to the load.

Sensitivity. For an ammeter, the amount of current that will cause full-scale deflection of the meter. For a voltmeter, the ratio of the voltmeter resistance divided by the full-scale reading of the meter; expressed in ohms per volt. The ability of a receiver to reproduce very weak signals. The greater the receiver sensitivity, the weaker the signal that can be reproduced. Efficiency of a microphone. Describes microphone power delivered to a matched-impedance load as compared to the sound level being converted. Usually expressed in terms of the electrical power level.

Sensor. A transducer that produces an electrical output based some input [electrical, mechanical and so on]. A device, usually electronic, that extends man's natural senses by means of emitted or reflected energy. The energy may be nuclear, electromagnetic including the visible and invisible portions of the spectrum, chemical, biological, thermal, or mechanical. Related page; Sensor Manufacturers.

Sequential Access. The reading or writing of data in a sequential order as opposed to random access.

Sequential Logic Element. A device that has at least one output channel and one or more input channels, all characterized by discrete states, such that the state of each output channel is determined by the previous states of the input channels. A State Machine.

SERDES. An electronic component that converts parallel data to serial and serial data to parallel.

Serial Access. Pertaining to the sequential or consecutive transmission of data into or out of a device, such as a computer, transmission line, or storage device.

Serialize. The process of converting parallel data into serial data.

Serial Port. A port through which data are passed serially, i.e., one bit at a time, and that requires only one input channel to handle a set of bits, e.g., all the bits of a byte. The RS232 Serial Port was the common interface found on personal computers.

Serial-to-Parallel Conversion. Conversion of a stream of data elements received in time sequence, i.e., one at a time, into a data stream consisting of multiple data elements transmitted simultaneously. A Shift Register with a serial input and parallel output could act as a Serial-to-Parallel converter.

Serial Transfer. The transfer of information over a single path in which data bits are sent one at a time.

Series Circuit. An arrangement where electrical devices are connected so that the total current must flow through all the devices; electrons have one path to travel from the negative terminal to the positive terminal.

Series-Connected Duplexer. A configuration in which the tr spark gap is connected in series in one leg of the transmission line one-half wavelength away from the T-junction.

Series-Diode Detector. The semiconductor diode in series with the input voltage and the load impedance. Sometimes called a Voltage-Diode Detector.

Series-Fed Oscillator. An oscillator in which dc power is supplied to the amplifier through the tank circuit or a portion of the tank circuit. Also refer to an example Series-Fed Armstrong Oscillator circuit.

Series Feedback. Current Feedback.

Series Limiter. A diode connected in series with the output, in which the output is taken across the resistor. Either the positive or negative alternation of the input wave is eliminated.

Series Motor. A motor that has the armature and field coils in series and which carry the same current.

Series-Negative Limiter. A diode connected in series with the output, in which the output is taken across the resistor. It eliminates the negative alternation of the input wave.

Series-Parallel Circuit. A circuit that consists of both series and parallel networks.