2
Theory of Operation
The AEDR-8300-1Wx combines an emitter and a detector
in a single surface mount leadless package. When used
with a codewheel or linear codestrip, the encoder trans-
lates rotary or linear motion into digital outputs. As seen
in the block diagram, the AEDR-8300-1Wx consists of
three major components: a light emitting diode (LED)
light source, a detector IC consisting photodiodes and
lens to focus light beam from the emitter as well as light
falling on the detector.
Block Diagram of AEDR-8300-1Wx
SIGNAL
PROCESSING
CIRCUITRY
V
CC
CH A
V
LED
GND
CH B
GND
R
CODEWHEEL
or
CODESTRIP
Denitions
State Width (S): The number of electrical degrees between
a transition in Channel A and the neighboring transition
in Channel B. There are 4 states per cycle, each nominally
90°e.
State Width Error (∆S): The deviation of state width, in elec-
trical degree, from its ideal value of 90°e.
Phase (φ): The number of electrical degrees between the
center of high state of Channel A and the center of high
state of Channel B. Nominally 90°e.
Phase Error (∆φ): The deviation of phase, in electrical
degree, from its ideal value of 90°e.
Pulse Width (P): The duration of high state of the output,
in electrical degree, within one cycle. Nominally 180°e or
half a cycle.
Pulse Width Error (∆P): The deviation of pulse width, in elec-
trical degree, from its ideal value of 180°e.
Count (N): The number of window and bar pair per revolu-
tion (CPR) of codewheel. For linear codestrip, dened as
the number of window and bar pair per unit length (lines
per inch [LPI] or lines per mm [LPmm]).
One Cycle (C): 360 electrical degrees (°e). Equivalent to one
window and bar pair.
One Shaft Rotation: 360 mechanical degrees. Also equiva-
lent to N counts (codewheel only).
Line Density: The number of window and bar pair per unit
length, expressed in either lines per inch (LPI) or lines per
mm (LPmm).
Optical radius (Rop): The distance between the codewheel
center and the centerline between the two domes of the
encoder.
Gap (G): The distance from surface of the encoder to the
surface of codewheel or codestrip.
Radial and Tangential Misalignment Error (E
R
, E
T
): For rotary
motion, mechanical displacement in the radial and tan-
gential directions relative to the nominal alignment.
Angular Misalignment Error (E
A
): Angular displacement of
the encoder relative to the tangential line.
Specular Reectance (R
f
): The amount of incident light
reected by a surface. Quantied in terms of the per-
centage of incident light. A spectrometer can be used to
measure specular reectance of a surface (contact factory
for more information).
The operation of the encoder is based on the principle of
optics where the detector photodiodes sense the absence
and presence of light. In this case, the rotary/linear motion
of an object being monitored is converted to equiva-
lent light pattern via the use of codewheel/codestrip. As
shown in the above diagram, the reective area (window)
of the codewheel (or codestrip) reects light back to the
photodetector IC, whereas no light is reected by the
non-reective area (bar). An alternating light and dark
patterns corresponding to the window and bar fall on
the photodiodes as the codewheel rotates. The moving
light pattern is exploited by the detector circuitry to
produce digital outputs representing the rotation of the
codewheel. When the codewheel is coupled to a motor,
the encoder outputs are then a direct representation of
the motor rotation. The same concept applies to the use
of a codestrip to detect linear motion.
