Technical Glossary - D

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D-AMPS
Digital Advanced Mobile Phone System. An American standard for digital mobile telephony used primarily in North America, Latin America, Australia and parts of Russia and Asia, now commonly referred to as TDMA.

dB
(see "decibel")

dBm
An abbreviation for decibels referred to one milliwatt. A term used to denote power level; i.e. 0 dBm is equal to 1 milliwatt.

DC Bias
(See "bias")

DC
(See "direct current").

DCS 1800
A variant of GSM operating at or near 1.8 GHz.

DCS 1900
A variant of GSM operating at or near 1.9 GHz used in the United States.

deci
A prefix which indicates a factor 10-1 (one tenth). Abbreviated as "d."

Decibel
One tenth of a Bel (B). The abbreviation for decibel is "dB." If N = P1/P2 is the ratio of two powers, then this ratio, N, expressed in decibels, is N = 10 log10(P1/P2).

DECT
Digital European Cordless Telephone.

deka
A prefix that indicates a factor 10, abbreviated as "da."

Delay Line
A transmission line or circuit that imposes a desired amount of propagation delay on an incident signal. Delay lines may also be specified in terms of the phase shift they produce as a result of the propagation delay.

Delta
Arithmetic difference between two numbers, or the change in value of a parameter.

Demodulation
The process of recovering intelligence from a signal, some parameter of which was modified to carry the intelligence (see modulation).

Depletion Layer
The insulating region in a rectifying semiconductor junction immediately surrounding and including the junction, caused by the space charge that occurs at the junction, which acts to deplete the concentration charge carriers in the region.

Desensitization
The reduction in receiver sensitivity that is the result of the presence of large magnitude, off-channel signals.

Detector
A circuit that produces a low frequency output signal, typically DC or video, whose amplitude is dependent upon the RF incident power level. The semiconductor element in a detector is typically a Schottky diode, FET or a tunnel diode.

Dielectric
A dielectric material is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic fields. Placing a dielectric between two metal plates, across which a voltage is applied, results in a slight separation of the positive and negative charges in the dielectric. This charge separation helps support the electric field between the plates and can store energy. This property is useful in capacitors, especially at radio frequencies. Dielectric materials are also used in the construction of radio-frequency transmission lines.

Dielectric Constant
The property of a material that determines the amount of electrostatic energy that is stored per unit volume per unit voltage gradient. Relative dielectric constant relates this ability for a given material to that of a vacuum.

Dielectric Loss
The time rate at which electric energy is converted into heat energy in a dielectric that is subjected to a varying electric field.

Diffusion
The movement of electrical charge carriers or particles from regions of high concentration to regions of lower concentration. In semiconductor fabrication, the movement of impurity atoms during high temperature annealing.

Digital
Having or pertaining to the use of numbers expressed in digits to represent all of the variables of a system. Using, pertaining to, or consisting of that class of devices whose performance varies only in discrete steps.

Diode
A two-terminal device which has nonlinear and asymmetrical (about zero) voltage versus current characteristics.

Diplexer
A circuit or system that allows the ability to transmit and receive two distinct signals simultaneously.

Diplexing
The simultaneous transmission or reception of two signals though a common component, such as an antenna.

Direct Current
A flow of charge carriers within a medium in a single direction.

Directional Coupler
|A four port device that transmits the majority of signal power incident on its input port to the output port and the remainder of the signal power to a third, coupled port. Signals incident on the output port are coupled to the fourth, coupled port, which may be terminated with a resistor equal in value to the coupler's characteristic impedance. The ratio of the coupled power to the input power is the coupling factor.

Discrete
Complete in and of itself. In electronics, a discrete component consists of a single circuit element in a package, for example a diode or transistor. In practice, some components considered discrete may actually consist of a few simple circuit elements in a single package.

Discriminator
A tuned circuit that produces an output voltage, the amplitude and polarity of which are determined by the frequency of the input signal. A discriminator is used as the demodulator in an FM receiver.

Dissipation
The conversion of electrical energy to heat energy in a component.

Distortion
Undesired changes in a waveform that result in spurious content of the signal.

Distributed Capacitance
Capacitance that is not concentrated within a lumped capacitor, but spread over a circuit or group of components.

Distributed Inductance
Inductance that is not concentrated within a lumped inductor, but spread over a circuit or group of components.

Donor
A material that is intentionally added to a pure semiconductor material in order to increase the population of free electrons in that semiconductor, resulting in a net negative charge. A semiconductor that has had donor material added to it is called "n-type."

Dopant
An impurity added to a pure substance to alter the behavior or properties of the pure substance. Dopants in semiconductors are either charge carrier donors or acceptors, and make the semiconductor either n-type (surplus electrons), or p-type (shortage of electrons).

Doping
The intentional addition of a foreign substance to a pure substance in order to alter the behavior or properties of the pure substance.

Doppler Effect
The apparent shift in frequency of an incident wave that is the result of relative velocity between the emitter of the wave and the receiver of the wave. The Doppler shift frequency (fd) is given by:
fd = 2 V (f0 / c) cosF, where:
f0 is transmitter frequency in Hz,
c is velocity of light (3 x 108 meters per second),
V is the magnitude of the relative velocity (meters per second),
æ is the angle between the incident wave and target's path.
Note: cos æ is 1 for motion directly toward or away from the receiver. Velocity (V) is a vector that determines the sign of doppler shift frequency.

Doppler Radar
A radar system that uses the Doppler effect to measure presence and velocity of a target. The commercial Doppler systems, such as police radars and intrusion alarms, usually operate with a "zero IF" because the transmitter source (Gunn oscillator) is also used as the local oscillator for the mixer. Using this technique, the frequency of the IF signal is the Doppler shift frequency. For example, if the transmitter frequency is 10.525 GHz, a vehicle traveling at 50 mph will cause a Doppler shift of 1568 Hz.

Doppler Shift
(See "Doppler Effect").

Double Balanced Mixer
A frequency translation circuit, which consists of four components with nonlinear impedance, typically Schottky diodes or FET's, connected in a ring quad configuration, with balun transformers at the RF and LO inputs to connect unbalanced transmission lines to the balanced quad. The IF output is via an unbalanced transmission line. The term balanced mixer is used to imply that neither of the input terms will appear at the mixer output. In practice, suppression of these input components is never perfect in an analog mixer circuit. Both types of mixer produce signals at odd harmonics of the carrier frequency, particularly the diode ring mixer. In most cases, these can be easily filtered out.

Downconverter (Mixer)
A mixer whose desired output signal called the IF signal is the difference of the incident RF and LO signals.

DQPSK
Differential quadrature phase shift key modulation.

Drain
The terminal at one end of the channel of a field effect transistor (FET) from which electron or hole current leaves the channel. This terminal corresponds to the collector in a bipolar transistor.

Driver
A circuit that supplies an input to another circuit, and (usually) provides a level boost, impedance matching, or isolation.

DSSS
Direct Sequence Spread Spectrum. A transmission technique that uses a pseudo-random, noise-like modulation code to widen the spectrum of the transmitted signal.

Duplex
The ability in a communications systems to simultaneously transmit and receive signals through a common component such as an antenna.

Duplexer
A circuit or component that allows a communications system to simultaneously transmit and receive signals through a common component, such as an antenna. Such systems typically use different frequencies for the transmit and receive signals, so the duplexer is often a pair of filters, each tuned to pass the desired signal frequency and reject the other signal frequency.

Duroid
A commercially available product used to make microwave printed circuit boards, especially those employing microstrip, strip line and coplanar waveguide transmission line structures. The dielectric layer of Duroid" is tightly controlled and is available with a number of different relative dielectric constants and physical thicknesses.

Duty Cycle
The ratio of operating to non-operating time for a device.

Dynamic Range
The power range over which a component or system functions properly.