2
Theory of Operation
The AEDR-8300 series combines an emitter and a detec-
tor in a single surface mount leadless package. When
used with a codewheel or linear codestrip, the encoder
translates rotary or linear motion into digital outputs.
As seen in the block diagram, the AEDR-8300 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.
The operation of the encoder is based on the principle
of optics where the detector photodiodes sense the ab-
sence and presence of light. In this case, the rotary/lin-
ear motion of an object being monitored is converted
to equivalent light pattern via the use of codewheel/
codestrip. As shown in the diagram below, 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 ro-
tates. The moving light pattern is exploited by the de-
tector circuitry to produce digital outputs representing
the rotation of the codewheel. When the codewheel is
coupled to a motor, the encoder outputs is then a direct
representation of the motor rotation. The same concept
applies to the use of a codestrip to detect linear motion.
Figure 1. Block Diagram of AEDR-8300.
AEDR-8300 block diag
V
LED
GND
V
CC
CH A
CH B
GND
SIGNAL
PROCESSING
CIRCUITRY
R
CODEWHEE
Denitions
State Width (S): The number of electrical degrees be-
tween a transition in Channel A and the neighboring
transition in Channel B. There are 4 states per cycle,
each nominally 90
o
e.
State Width Error (∆S): The deviation of state width, in
electrical degree, from its ideal value of 90
o
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
o
e.
Phase Error (∆φ): The deviation of phase, in electrical
degree, from its ideal value of 90
o
e.
Pulse Width (P): The duration of high state of the out-
put, in electrical degree, within one cycle. Nominally
180
o
e or half a cycle.
Pulse Width Error (∆P): The deviation of pulse width, in
electrical degree, from its ideal value of 180
o
e.
Count (N): The number of window and bar pair per rev-
olution (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 (
o
e). Equivalent to
one window and bar pair.
