Patent ID: 8334495

Claim:
A photometric device comprising: a constant current generation circuit configured to output a constant current; a first clock signal generation circuit configured to generate a first clock signal, the first clock signal oscillating at a frequency proportional to the constant current, the first clock signal generation circuit comprising: a first ramp signal generation circuit; a first hysteresis comparator circuit connected to the first ramp signal generation circuit; and a first buffer circuit connected to the first ramp signal generation circuit and the first hysteresis comparator circuit; a photoelectric conversion element configured to generate a photocurrent when receiving light; a second clock signal generation circuit configured to generate a second clock signal, the second clock signal oscillating at a frequency proportional to the photocurrent, the second clock signal generation circuit comprising: a second ramp signal generation circuit; a second hysteresis comparator circuit connected to the second ramp signal generation circuit; and a second buffer circuit connected to the second ramp signal generation circuit and the second hysteresis comparator circuit; and a digital signal generation circuit configured to count the number of pulses of the second clock signal, the digital signal generation circuit configured to output a digital signal including a count value of the number of pulses, the digital signal generation circuit configured to set a timing when counting of the number of pulses of the second clock signal starts and a timing when the counting finishes, based on the first clock signal.