2
Theory of Operation
The AEDx-8xxx optical encoder is a housed solution with
integrated encoder and codewheel. The encoder trans-
lates the rotary motion of a shaft into incremental digital
outputs.
The encoder contains a single Light Emitting Diode (LED)
as the light source. The light is collimated into a parallel
beam by means of polycarbonate lens located directly
over the LED. Opposite the emitter is a detector IC. This
IC consists of multiple sets of photo detectors and signal
processing circuitry necessary to produce the digital wave-
form output. The codewheel rotates between the emitter
and detector, causing the light beam to be interrupted by
pattern of spaces and bars on the codewheel. The Photo-
diodes that detect these interruptions are arranged in a
pattern that corresponds to the radius and design of the
codewheel. These detectors are also spaced in such way
that light period on one pair of detectors corresponds to
dark period on adjacent pair of detectors. The photodiode
outputs are then fed through the signal processing circuit-
ry that produce the nal outputs for channel A and B. Due
to this integrated phasing technique, the digital output of
channel A is in quadrature with that of channel B (90 elec-
trical degrees out of phase). As a standard, the outputs are
fed through a standard RS422 line driver to deliver the dif-
ferentials signals at the nal encoder output.
Denitions
Cycles (N): The number of electrical cycles per revolution
(CPR).
Note: 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 dif-
ference 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 be-
tween transitions in the output of channel A and the
neighboring 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.
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.
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.
Absolute Maximum Ratings
[1,2]
Parameter Symbol Min. Max. Units
1. Storage Temperature AEDS Series T
S
-20 85 ° C
Storage Temperature AEDT Series T
S
-40 100 ° C
2. Supply Voltage Vcc -0.5 7 V
3. Output Voltage Vout -0.5 Vcc V
4. Output Current per Channel Iout - ± 150 mA
5. Shaft Axial Play - ± 0.100 mm
6. Shaft Radial Play Plus Eccentricity - ± 0.080 mm
Note:
1. Absolute Maximum Ratings are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the
device should be operated at these limits.
2. Stresses greater than those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to absolute maximum
rating conditions for extended periods may aect reliability.
