2
Theory of Operation
The AEDT-9340 optical encoder is an emitter/detector
module. Coupled with a codewheel, these modules trans-
late the rotary motion of a shaft into a six-channel digital
output.
The modules contain a single Light Emitting Diode (LED)
as its light source. The light is collimated into a parallel
beam by means of a single polycarbonate lens located di-
rectly over the LED. Opposite the emitter is the integrated
detector circuit. This IC consists of multiple sets of photo
detectors and the signal processing circuitry necessary to
produce the digital waveforms.
The codewheel rotates between the emitter and detector,
causing the light beam to be interrupted by the pattern of
spaces and bars on the codewheel.
The photodiodes that detect these interruptions are ar-
ranged in a pattern that corresponds to the radius and
design of the code-wheel. These detectors are also de-
liberately spaced such that a light period on one pair of
detectors corresponds to a dark period on the adjacent
pair of detectors.
The photodiode outputs are then fed through the signal
processing circuitry resulting in A, /A, B, /B, I, and /I. Com-
parators receive these signals and produce the nal out-
puts for channels A and B. Due to this integrated phasing
technique, the digital output of channel A is in quadra-
ture with that of channel B (90 mechanical degrees out of
phase). The commutation feedback (U, V, W) signals are
generated based on the codewheel design.
Denitions
Count (N): The number of electrical cycles per revolution
(CPR). CPR refers to the raw signal from encoder that is
the cycles before 4x decode.
One Cycle: 360 electrical degrees (°e).
One Shaft Rotation: 360 mechanical degrees.
Cycle Error (∆C): An indication of cycle uniformity. The dier-
ence between an observed shaft angle which gives rise to
one electrical cycle, and the nominal angular increment of
1/N of a revolution.
Pulse Width (P): The number of electrical degrees that an
output is high during 1 cycle. This value is nominally 180°e
or 1/2 cycle.
Pulse Width Error (∆P): The deviation, in electrical degrees, of
the pulse width from its ideal value of 180°e.
State Width (S): The numbers of electrical degrees between
transitions in the output of channel A and the neighbor-
ing transition in the output of channel B. There are 4 states
per cycle, each nominally 90°e.
State Width Error (∆S): The deviation, in electrical degrees, of
each state width from its ideal value of 90°e.
Commutation Accuracy (∆I): The deviation, in mechanical de-
grees, after shaft rotates passes the reference point (Index
channel) to the rst U channel pulse. The measurement
from middle of channel I to channel U.
Phase (φ): The numbers of electrical degrees between the
center of the high state of channel A and the center of the
high state of channel B.
This value is nominally 90°e for quadrature output.
Phase Error (∆φ): The deviation of the phase from its ideal
value of 90°e.
Direction of Rotation: When the codewheel rotates in the
clockwise direction viewing from top of the module, chan-
nel A will lead channel B. If the codewheel rotates in the
opposite direction, channel B will lead channel A.
Optical Radius (Rop): The distance from the codewheel’s cen-
ter of rotation to the optical center (O.C) of the encoder
module.
Index Pulse Width (Po): The number of electrical degrees that
an index is high with reference to channel A or channel B
during one full shaft rotation
