EPC111 Datasheet, PDF (5/14 Pages) Espros Photonics corp – Fully integrated standalone light barrier driver & receiver

epc111/112
Functional Description
Evaluation of single light pulse
For each single light pulse, received and detected by the LED, the threshold levels are processed according to the following principle to
propagate the output signals OUTN and OUTH resp. OUTNINT and OUTHINT. As far the received light pulse signal exceeds the corresponding
threshold level, the pulse will be recognized as a valid pulse and the detection circuit sets the appropriate output signal OUTN INT or OUTHINT.
I_PD
Threshold levels:
Light reserve OUTH
Signal output OUTN
Light pulse detection
I_PD
Light reserve detection
t
t
OUTN_INT
t
t
OUTH_INT
t
t
Figure 3: Pulse evaluation
Pulse Modulated Operation (e.g. OUTNint to OUTN)
The epc111/112 chip operates the LED and the receiver path on a pulse modulated concept. Thus, the LED is operated with short pulses
whereas the receiver channel does synchronous demodulation of the received light pulses by reading the current pulses of the photodiode.
This concept allows a very high sensitivity, high speed operation, and a high suppression of input ambient or foreign light (DC currents)
generated by sunlight or other DC light sources like light bulbs.
In order to eliminate interference caused by modulated light, e.g. a flashing light or by other light barriers, the input signal from the photodiode
is amplified, filtered, and processed by an integrated signal processor. If the photodiode signal meets the required frequency, pattern and
amplitude, the output(s) are triggered. The following timing diagram shows the basic concept.
on
Emitter LED
off
t
Pulse
t
Cycle
yes
Beam interrupted no
Photo diode current I
PD
OUTN or OUTH
INT
INT
OUTN or OUTH ^[V]
1
2
n
M
t
F
Release time
missing pulses
1
2
n
V
t
R
Response time
valid (non-missing) pulses
Figure 4: Pulse modulation concept
It is in fact a digital filter which counts missing and non-missing pulses to change the ou tput state of OUTN or OUTH.
© 2011 ESPROS Photonics Corporation
5
Characteristics subject to change without notice
Datasheet epc111_112 - V2.2
www.espros.ch