Pulse light-receiving circuit with means to minimize power source noise

A pulse light-receiving circuit comprising:

• a first light-receiving element photoelectrically converting a pulse light into an electrical current;
• a first preamplifier amplifying the electrical current from said first light-receiving element;
• a second light-receiving element shielded from light;
• a second preamplifier, connected to said second light-receiving element and made up of a circuit equivalent to that of said first preamplifier for amplifying an output from said second light-receiving element;
• a primary difference amplifier amplifying a light-receiving element difference between output signals from said first preamplifier and said second preamplifier;
• an auxiliary difference amplifier for outputting a reference voltage, made up of a circuit equivalent to that of said primary difference amplifier, with both input terminals thereof being commonly connected to an output terminal of said second preamplifier;
• a first peak value-detecting circuit for obtaining a first peak value of an output from a first difference output terminal of said primary difference amplifier, said first difference output terminal being connected to said first peak value-detecting circuit;
• a second peak value-detecting circuit for obtaining a second peak value of an output from a second difference output terminal of said primary difference amplifier, said second difference output terminal being connected to said second peak value-detecting circuit;
• a median value calculator for calculating a median value between maximum and minimum values of the output from said first difference output terminal based on the reference voltage, the first peak value, and the second peak value;
• and
• a comparator comparing the median value to the output from said first difference output terminal.