Electronic Engineering Dictionary

Demodulation. The removal of intelligence from a transmission medium. The recovery, from a modulated carrier, of a signal having substantially the same characteristics as the original modulating signal.

Demodulator. A circuit used in servo-systems to convert an ac signal to a dc signal. The magnitude of the dc output is determined by the magnitude of the ac input signal, and its polarity is determined by whether the ac input signal is in or out of phase with the ac reference voltage.

DeMorgan's Theorem. A theorem which states that the inversion of a series of AND applications is equal to the same series of inverted OR applications, or the inversion of a series of OR applications is equal to the same series of inverted AND applications. Also refer to Timing Hazards for applications

Demultiplexing. The separation of two or more channels previously multiplexed; i.e., the reverse of multiplexing. A related topic; 1 to 4 Line Decoder IC.

Demux. Short for demultiplex or demultiplexer.

Density. The compactness of a substance. Mass per unit volume.

Depletion-Mode Operation. The operation of a FET such that changing the gate to source voltage from zero to a finite value decreases the magnitude of the drain current.

Depletion Region. The region in a semiconductor where essentially all free electrons and holes have been swept out by the electrostatic field which exists there. The region extending on both sides of a reverse biased semiconductor junction in which free carriers are removed from the vicinity of the junction.

Depletion-type FET. A FET having appreciable channel conductivity for zero gate to source voltage. The channel conductivity may be increased or decreased according to the polarity of the applied gate to source voltage.

Derate. The process of reducing the voltage, current or power rating to increase a components reliability. Using an item in such a way that applied stresses are below rated values.

Derating. The process of reducing a components power dissipation with increasing temperature to insure that the component remains at the same temperature. Derating applies to any device that allows current flow, Active, Passive or Mechanical. Guideline for Derating Electronic Components. The method of reducing stress and/or making quantitative allowances for a parts functional degradation. Consequently, derating is a means to reduce failures and extending part life. In addition, derating helps protect parts from unforeseen application anomalies and over-stresses.

De Sauty Bridge. A four element AC bridge use to measure capacitance. One half of the bridge contains a known capacitor and a variable resistor, and the other arm contains an unknown capacitance and a variable resistors. The resistors are adjusted until the current in the center is null between the two arms. The equation for the unknown capacitor equals R1C1 / R2.

Desiccant. A substance used as a drying agent. A desiccant is a substance that adsorbs water. Silica gel is a common desiccant, so is calcium chloride. Silica gel Synonyms: Hydrated silica; Silica gel; Precipitated silica; Silica, amorphous, precipitated and gel; Silica hydrate; Silicic acid.

Silica beads

Desiccant is sold as bulk or small unit bags. Desiccant is referenced in MIL-D-3463E Type I & II Specifications.

Design Margin. The additional performance capability above required standard basic system parameters that may be specified by a system designer to compensate for uncertainties. Also refer to Derating.