US 6,982,408 B2
Photo-detecting method and photo-detecting device with varying modulation frequency
Yasuhiro Maruyama, Kitakatsuragi-gun (Japan)
Assigned to Sharp Kabushiki Kaisha, Osaka (Japan)
Filed on Dec. 12, 2002, as Appl. No. 10/317,187.
Claims priority of application No. 2001-382083 (JP), filed on Dec. 14, 2001; and application No. 2002-358438 (JP), filed on Dec. 10, 2002.
Prior Publication US 2003/0127586 A1, Jul. 10, 2003
Int. Cl. G06M 7/00 (2006.01); H01J 40/14 (2006.01)
U.S. Cl. 250—221 9 Claims
OG exemplary drawing
 
1. A photo-detecting device, comprising:
an oscillation circuit provided with a plurality of constant current sources for outputting a plurality of signals having different oscillation frequencies;
light-emitting means for projecting toward an object a light that is pulse-modulated in response to a signal from said oscillation circuit;
light-receiving means for receiving either light reflected from the object or light transmitted through the object, and for converting the received light into a light-receiving signal;
counting means for counting the light-receiving signal a plurality of times in synchronism with a modulation frequency of the projected light;
detecting means for detecting the object in response to said counting means; and
frequency changing means for, in accordance with a count of the counting means, controlling the plurality of constant current sources to vary an oscillation frequency of said oscillation circuit in a determinable manner, while said counting means counts the light-receiving signal a plurality of times.