Browse Prior Art Database

Look-Across Sensor

IP.com Disclosure Number: IPCOM000103273D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Trudgen, GA: AUTHOR

Abstract

Disclosed is a look-across optoelectronic sensor system that operates in high ambient light environments. The heart of the system is the unique receiver circuit. Although simple and low-cost, it rejects the ambient signal while amplifying the transmitted signal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Look-Across Sensor

       Disclosed is a look-across optoelectronic sensor system
that operates in high ambient light environments.  The heart of the
system is the unique receiver circuit.  Although simple and low-cost,
it rejects the ambient signal while amplifying the transmitted
signal.

      The sensor system is shown in the figure.  The light-emitting
diode (LED) 1 emits a near-infrared light beam when the INPUT to
BUFFER 2 is high.  The duration of the beam is short, only long
enough to allow the darlington photo-transistor (PTX 3) time to
respond.  When an object enters the gap between the optoelectronic
pair, it blocks the LED emitted light beam from striking PTX 3.  When
this occurs, the OUTPUT from COMPARATOR 4 remains low, indicating
that the emitted LED light pulse was not received.

      The LED light pulse and incident ambient light generates a
composite signal current that flows in the collector of PTX 3.  The
ambient signal rate of change is very slow compared to the abrupt
signal from LED 1.  Thus, the PTX 3 signal current is a slow changing
current modulated by a pulse of current.  It is required that only
the modulated portion of the signal be detected.

      By using INDUCTOR 5 as the load element for PTX 3, a
transimpedance amplifier is configured which amplifies the two signal
components at different rates.  The gain is low for the ambient light
portion of the signal, and the gain is high for the abrupt change of
current f...