Patent ID: 7948483

Claim:
A photo detection circuit comprising: a photodiode whose cathode is connected to a high-potential-side power supply and whose anode is connected to a connection point; a capacitor element provided between the connection point and a low-potential-side power supply; and a switching element, provided between the connection point and the low-potential-side power supply, that switches on and off based on a repeating reset pulse signal, the repeating reset pulse signal repeating with a first predetermined frequency, and an output circuit converting a voltage signal of the connection point into a plurality of pulse signals having a second predetermined frequency and outputting the plurality of pulse signals only while the voltage signal of the connection point is substantially equal to a voltage of the high-potential-side power supply and until the switching element is turned on, the switching on and off of the switching element corresponding with the repeating reset pulse signal supplied to the photo detection circuit, the repeating reset pulse signal having a pulse width equal to one full cycle of one pulse signal of the plurality of pulse signals that includes a high pulse and an adjacent low pulse.