Photoelectric sensor, control method therefor and semiconductor integrated circuit therefor

A photoelectric sensor comprising:

• light transmitting means for transmitting pulsed light repetitively by driving a light transmitting element at a specified light transmission timing;
• light receiving means for receiving light and outputting an electrical reception signal corresponding to said received light;
• first level judging means for comparing the level of said reception signal with a specified first threshold value, thereby judging the level of said reception signal at a level-judging timing which is slightly delayed from said light transmission timing;
• signal processor means for generating a sensor output based upon the result of a comparison by said first level judging means;
• second level judging means for comparing the level of said reception signal with a second threshold value proximal to an AC zero level, thereby judging the level of said reception signal;
• and
• transmission timing control means for controlling the timing of next light transmission from said light transmitting means based upon the result of a comparison by said second level judging means.

A semiconductor integrated circuit for a photoelectric sensor having a light transmitting element and a light receiving element, said integrated circuit comprising:

• a first external terminal for supplying power;
• a second external terminal for outputting a transmission controlling signal for a driver circuit for said light transmitting element;
• a third external terminal for outputting a sensor load controlling signal for a driver circuit for sensor load;
• a power source circuit for receiving power through said first external terminal and providing a stabilized power source for internal circuits of said semiconductor integrated circuit;
• a light receiving circuit for outputting a reception signal according to light received by said light receiving element;
• a light transmitting circuit for outputting said transmission controlling signal to said second external terminal;
• an output circuit for outputting said sensor load controlling signal to said third external terminal;
• and
• a signal processor circuit for controlling said output circuit and said light transmitting circuit by said reception signal received from said light receiving circuit;
• wherein said light receiving circuit, said light transmitting circuit, said output circuit and said signal processor circuit are integrated;
• wherein said signal processor circuit comprises:
• a first level judging means for comparing said reception signal with a specified threshold value at a timing slightly delayed from the timing of light transmission from said light transmitting element;
• a signal processing means for generating a sensor output according to a result of comparison by said first level judging means and supplying said sensor output to said output circuit;
• a second level judging means for comparing said reception signal with another threshold value near an AC zero level;
• and
• a light transmission timing controlling means for supplying to said light transmitting circuit a light transmission timing control signal for controlling the timing of next light transmission from said light transmitting element according to the comparison by said second level judging means.