DQE
See
detective quantum efficiency
.
DRA
See
dielectric resonator antenna
.
drain
terminal of an FET (usually identi-
cal in structure to the source) to which elec-
trons flow. Electrons in the FET channel flow
down the drain, and current flow is defined as
the negative direction of electron movement,
since electrons are negative. In p-channel
FETs, current flows from source to drain. In
n-channel FETs, current flows from drain to
source. The drain is usually considered to be
the metal contact at the surface of the die.
drain conductance
the increase in drain
current when the magnitude of the applied
FET drain-to-source voltage is increased.
Mathematically, the derivative of drain cur-
rent with respect to drain voltage.
drain saturation current
the drain-to-
source current flow through the JFET under
the conditions that
V
GS
= 0 and | V
DS
|>|
V
P
| such that the JFET is operating in the
active or saturated region.
drain-source leakage
the current flowing
in the channel of a MOSFET when its gate
and source are shorted together. The mag-
nitude of the leakage current is strongly in-
fluenced by the applied drain-source voltage,
the gate length and substrate doping concen-
tration.
drain-to-source voltage (VDS)
poten-
tial difference between the FET drain and
source terminals, this voltage determines the
device operational region and limits the out-
put power. For an n-channel device this volt-
age is normally positive, and negative for a
p-channel device. Magnitudes usually range
up to as high as 10 V for a low noise device
and much higher for power devices.
DRAM
See
dynamic random access
memory
.
drift
(1) movement of free carriers in a
semiconductor due to the electric field.
(2) the relatively uninpaired fluctuation
of adaptive filter coefficients in the direc-
tion of least sensitivity along the eigenvector
corresponding to the minimum eigenvalue is
known as coefficient drift.
Coefficient drift can be a problem if this
eigenvalue gets very small, as coefficients
can drift out of the allowed region. Also
important as random, often temperature-
induced, fluctuations in the output levels of
DC amplifiers.
drift chamber
a series of chambers used
to detect particle trajectories. They are simi-
lar to multi-wire proportional chambers, ex-
cept the wire spacing is increased. The cor-
relation between the position of an ionized
track produced by a charged particle and the
time of appearance of an electric pulse at the
wire is used to measure the distance of the
trajectory from the wires.
drift space
space where electrons move
due only to their inertia.
drip-proof machine
a machine with ven-
tilating openings constructed in such a way
that drops of liquid or solid particles falling
on it, at an angle less than 15 degrees from
the vertical, can enter the machine neither
directly nor by striking on it, run along a hor-
izontal or inwardly inclined surface.
drive circuit
a circuit that produces gate
trigger pulses, of desired level and timing, to
turn on and off active switches (just turn on
for natural-commutated switches) in switch-
ing circuits.
driving-point admittance
the admittance
measured at the antenna terminals when the
antenna is in free space (not loaded).
DRO
See
dielectric resonator (stabled)
oscillator
.
c
2000 by CRC Press LLC