ET 8001
6-Channel precision amplifier with automatic hysteresis tracking function for encoders
OPTOLAB Microsystems GmbH, Haarbergstr. 61, 99097 Erfurt / Germany, Tel.: ++49-361-422 906-0, Fax ++49-361-422 906 50
We reserve the right to make technical changes at any time without prior notice.
More detailed technical information can be supplied upon request.
Features
Designed for optical encoders and
light barriers
Automatic Hysteresis monitoring and
tracking function generates precise
digital outputs
Phase stable outputs over a wide
range of conditions
No thermal drift or LED optical power
degradation problems from 40 to
+85 C.
Applications
Optical Encoders absolute, multiturn,
incremental.
Light barriers
Absolute Maximum Ratings
Ambient Temperature
-40 C to +85 C *
Supply Voltage
4.0 V to 5.5 V
Output Drive Capability
4 mA
* extended temperature range up to 125C
available
Functional Description
The ET8001 solves one of the most common problems in the encoder world the phase angle stability of the
digital outputs of an optical or magnetic al encoder under changing operating conditions.
During the lifetime of an encoder, the LED as a lightsource is degrading continuously.
At higher ambient temperatures the optical power output of an LED is up to 40% lower than it is at room
temperature.
All these variations are unwanted, because they change the phase angle of the digital outputs. Thus, if the
encoder has i.e. 12 bit, the gray or binary ,,word" can be siginificantly distorted ( please see table 1 ).
This problem has led to the "differential reading" of the tracks of the code disc. This method is unaffected by
light level changes but very expensive to manufacture and difficult to maintain in absolute encoders.
To overcome these problems, OPTOLAB as a specialist in optical sensors for encoders for more than 12 years
has developed the ET8001. This integrated circuit does :
Light tracking
Automatic hysteresis control and setting
Error signal
For high performance optical or magnetical encoders
Package: SO16 small outline
ET 8001
6-Channel precision amplifier with automatic hysteresis tracking function for encoders
OPTOLAB Microsystems GmbH, Haarbergstr. 61, 99097 Erfurt / Germany, Tel.: ++49-361-422 906-0, Fax ++49-361-422 906 50
We reserve the right to make technical changes at any time without prior notice.
More detailed technical information can be supplied upon request.
Electrical Characteristics
(Values are at 25 C and VCC = 5.5 V, unless otherwise noted)
VCC = 4.0 - 5.5V ; Ta = -40C to +85C
Parameter
Pin
Condition
Min
Max
Unit
Trigger level
HIGH(Offset)
IN
HYSH =550mV
HYSL = 450mV
540
560
mV
Trigger level
LOW(Offset)
IN
HYSH =550mV
HYSL = 450mV
440
460
mV
Input voltage
range
IN,HYSH, HYSL
VCC = -4.0 to
5.5V
0
VCC-2V
V
Input current
IN,HYSH
HYSL
Vin = 0V to VCC
- 2V
+/-1
A
Supply current
VCC
2.5
mA
Output voltage
LOW
O
HYSH =550mV
HYSL=450mV
Vin =0V
Ioutl = 4mA
0.4
V
Output voltage
HIGH
O
HYSH =550mV
HYSL=450mV
Vin =1V
Iouth = 4mA
VCC-0.8V
V
Risetime / falltime
IN,O
See test circuit
0,2
s
Test circuit
With an conventional encoder design the analog
output signal of the data track sensor varies due to
LED conditions. The hysteresis is fixed at the
designed level. If the signal weakens and the hyst-
eresis stays the same a ,,shrinking" output signal is
the result.
With the ET 8001 the hysteresis is not fixed. Track
is kept about the actual LED power and the
hysteresis is tied to this level, thus always following.
As seen in the lower image, the margin of
Hysteresis High and Low is much smaller, due to
smaller optical power. As a result you get a perfect
digital output !
ET 8001
6-Channel precision amplifier with automatic hysteresis tracking function for encoders
OPTOLAB Microsystems GmbH, Haarbergstr. 61, 99097 Erfurt / Germany, Tel.: ++49-361-422 906-0, Fax ++49-361-422 906 50
We reserve the right to make technical changes at any time without prior notice.
More detailed technical information can be supplied upon request.
Application Note
This application note describes an "easy to build" high performance 12 bit optical encoder. As sensor there is a
12bit high speed photo transistor array ( with or without premounted reticle/grating) available from OPTOLAB.
For "bullett proof " output linedrivers we recommend our ET7272. Short circuit proof up to 30V, 4in8out
channels and an operating voltage from 3.3 to 30 V makes a big difference !
Description
We can see 12 data tracks and one "monitor" track . The monitor photo transistor (PT) should be constantly
illuminated by the LED ( which is also illuminating the data tracks ).
The resistors R1 and R2 are used to set the HYSH ( High level ) and HYSL ( Low level ) of the hysteresis. There
are no trimpots needed in manufacturing.
To set the system and find the right values for the resistors following lab procedure is recommended :
1. Switch on LED, measure one DATA track, which is fully lit. Adjust the load resistor ( R
L
) until you see 1V at
the emitter of the PT. ( we have found values of 4 8 Kohm, depending on LED power ). This voltage we
call herein "signal". Use the same load resistor value for all data tracks.
2. 50% of our signal is the hysteresis center, in our example 500mV. Now we want to set the ET8001 to switch
precisely ON at 550mV and OFF at 450mV, no matter what. This is done by the resistors R1 and R2 ( a
total of 10K might do it ).
3. By varying R1 the hysteresis window width ( high and low trip points ) can be adjusted ( set 550mV to
appear at HYSH and set 450mV to appear at HYSL )
4. By varying R2 the center of the hysteresis window ( all more up or down the sine wave ) can be adjusted.
5. All
set
!
When finished, turn on your encoder, let the disc spin and watch the digital outputs. Vary the LED current to simulate
degradation or high temperature. You will find no change of the phase of the digital outputs at all !
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