Patent ID: 7489390

Claim:
A pulse light receiving time measurement apparatus comprising: a light receiving element receiving reflected pulse light from an object to be measured; a pulse light receiving time measurement circuit measuring a time when pulse light is irradiated to the object to be measured and a time when the reflected pulse light from the object to be measured is received at the light receiving element; a resonance circuit converting an optical pulse signal of the reflected pulse light from the light receiving element into a damping signal; a multi-stage amplifier group amplifying the damping signal from the resonance circuit; a damping signal processing circuit composed of amplitude comparators and zero-cross comparators, and processing the damping signal from each stage of the multi-stage amplifier group which is connected with a pair of an amplitude comparator and a zero-cross comparator, the amplitude comparators comparing amplitude of the damping signal with a predetermined value, the zero-cross comparators detecting that the damping signal crosses a bias level; and an integrated logic circuit combining a plurality of signal lines from the zero-cross comparator into one for output to the pulse light receiving time measurement circuit, wherein operations of the respective zero-cross comparators are determined according to comparison results of the respective amplitude comparators for the amplifier group.