Photodetecting circuit with compensated integration signal

• US 5,036,187 A
• Filed: 05/02/1990
• Issued: 07/30/1991
• Est. Priority Date: 05/08/1989
• Status: Expired due to Term

• Current Assignee: Dowa Mining Company Limited
• Original Assignee: Dowa Mining Company Limited
• Inventors: Yoshida, Shigeo, Fujimoto, Isamu
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Messinger, Michael
• Application Number:
  US07/517,769
• Time in Patent Office: 454 Days
• Field of Search: 250/221, 250/222.1, 250/214 B, 250/214 C, 341/5, 341/24, 341/31, 340/712
• US Class Current: 250/214.00B
• CPC Class Codes: G01V 8/20 using multiple transmitters or receivers
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen

Abstract

The optical input detection apparatus is adapted to integrate the value of the light received corresponding to the sum of the value of the light received by the light receiving device during driving of the light emitting device and the external flood light, deduct from the integration value the value of the light received equivalent to the external flood light received by the photodetector during the non-driving period following the driving of the light emitting device, compensate the integration value to the signal corresponding to the light emitting output and output the compensated signal to the comparator for comparison. Consequently, the presence or absence of an interruption in the light beam may be detected without being affected by the external flood light.

Claims

1. A photodetecting circuit having at least one pair of a light emitting device and a photodetector spaced from each other for a specified distance and adapted to detect presence or absence of interruption of a light beam emitted from said light emitting device to said photodetector, comprising:

means for integrating a light reception signal representing a value of light received by said photodetector while said light emitting device is driven to provide an integrated signal;

means for acquiring a compensated integration signal by deducting from said integrated signal an external flood light signal representing a value of an external flood light received by said photodetector in a non-driving period of said light emitting device following the driving of said light emitting device; and

means for comparing said compensated integration signal with a reference signal, thereby detecting the presence or absence of an interruption in said light beam without being affected by the external flood light;

wherein durin one detection period, said light emitting device is successively driven and not driven for equal periods for a plurality of times, and said compensated integration signal has a value obtained by deducting the external flood light during the respective non-driving periods from the integration value of the light reception signal during the respective driving periods.

2. A photodetector circuit having at least one pair of a light emitting device and a photodetector spaced from each other for a specified distance and adapted to detect presence or absence of an interruption of a light beam emitted from said light emitting device to said photodetector, comprising:

means for driving the light emitting device in successive on and off periods of approximately equal duration, for a predetermined detection time;

means for integrating a light reception signal representing a value of light received by said photodetector during the on period of said light emitting device to provide a first integrated signal, and for integrating an external flood light signal representing a value of an external flood light received by said photodetector during the off period of said light emitting device to provide a second integrated signal;

means for producing a compensated integration signal by deducting said second integrated signal from said first integrated signal during each of the off periods of the detection time; and

means for comparing said compensated integration signal with a reference signal to detect the presence or absence of the interruption in said light beam during the detection time.