AEDR-8400 Series
Reflective Surface Mount Optical Encoder
Data Sheet
Description Features
Reflective technology
The AEDR-8400 encoder is the smallest optical encod-
er employing reflective technology for motion control
Surface mount leadless package
purposes. The encoder houses an LED light source and a
Two channel quadrature digital outputs for direction
photo-detecting circuitry in a single package.
sensing
TTL compatible
The AEDR-8400 encoder offers two-channel quadrature
digital outputs. Being TTL compatible, the outputs of the
Single 2.8V supply
AEDR-8400 encoder can be interfaced directly with most
-20C to 85C absolute operating temperature
of the signal processing circuitries. Hence the encoder
Encoding resolution:
provides great design-in flexibility and easy integration
254 (lines/inch) or 10 (lines/mm)
into existing systems.
318 (lines/inch) or 12.5 (lines/mm)
Applications
Ideal for high volume applications:
Printers
Copiers
Card readers
Scanners
Digital Still Cameras
Camcorders
Camera Phones
Projectors
Consumer Product Applications
Note: Avago Technologies encoders are not recommended for use in safety critical applications such as. ABS braking
systems, power steering, life support systems and critical care medical equipment. Please contact our sales represen-
tative if clarification is needed.Theory of Operation
The AEDR-8400 encoder combines an emitter and a de- State Width Error (S): The deviation of state width, in elec-
tector in a single surface mount leadless package. When trical degree, from its ideal value of 90e.
used with a codewheel or linear codestrip, the encoder
Phase (): The number of electrical degrees between the
translates rotary or linear motion into digital outputs.
center of high state of Channel A and the center of high
As seen in the block diagram, the AEDR-8400 consists
state of Channel B. Nominally 90e.
of three major components: a light emitting diode (LED)
light source, a detector IC consisting photodiodes and
Phase Error ( ): The deviation of phase, in electrical de-
lens to focus light beam from the emitter as well as light
gree, from its ideal value of 90e.
falling on the detector.
Pulse Width (P): The duration of high state of the output,
in electrical degree, within one cycle. Nominally 180e
Block Diagram of AEDR-8400 Encoder
or half a cycle.
V
LED Pulse Width Error ( P): The deviation of pulse width, in elec-
trical degree, from its ideal value of 180e.
Gnd
Count (N): The number of window and bar pair per revolu-
V
CC
tion (CPR) of codewheel. For linear codestrip, defined as
the number of window and bar pair per unit length (lines
Signal
Ch A
per inch [LPI] or lines per mm [LPmm]).
Processing
Ch B
Circuitry
One Cycle (C): 360 electrical degrees (e). Equivalent to one
window and bar pair.
Codestrip or
Gnd
Codewheel
One Shaft Rotation: 360 mechanical degrees. Also equivalent
Note: Drawing not to scale.
to N counts (codewheel only).
The operation of the encoder is based on the principle
Line Density: The number of window and bar pair per unit
of optics where the detector photodiodes sense the
length, expressed in either lines per inch (LPI) or lines per
absence and presence of light. In this case, the rotary/
mm (LPmm).
linear motion of an object being monitored is converted
Optical radius (Rop): The distance between the codewheel
to equivalent light pattern via the use of codewheel/
center and the center of the encoder dome.
codestrip. As shown in the above diagram, the reflective
area (window) of the codewheel (or codestrip) reflects
Gap (G): The distance from surface of the encoder to the
light back to the photodetector IC, whereas no light is
surface of codewheel or codestrip.
reflected by the non-reflective area (bar). An alternating
Radial and Tangential Misalignment Error (E , E ): For rotary mo-
light and dark patterns corresponding to the window and R T
tion, mechanical displacement in the radial and tangen-
bar fall on the photodiodes as the codewheel rotates. The
tial directions relative to the nominal alignment.
moving light pattern is exploited by the detector circuitry
to produce digital outputs representing the rotation of
Angular Misalignment Error (E ): Angular displacement of the
A
the codewheel. When the codewheel is coupled to a mo-
encoder relative to the tangential line.
tor, the encoder outputs are then a direct representation
of the motor rotation. The same concept applies to the Specular Reflectance (R ): The amount of incident light
f
use of a codestrip to detect linear motion. reflected by a surface. Quantified in terms of the per -
centage of incident light. A spectrometer can be used to
measure specular reefl ctance of a surface (contact factory
Definitions
for more information).
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
90e.
Angular (E )
A
Radial (ER))
Tangential (E )
T
Codestrip or Codewheel
AEDR-8400
AEDR-8400
Gap
Shaft
Shaft
Codewheel
Codewheel
Note: Drawing not to scale
2