Signal processing device having a function of converting an analog signal into a digital signal

Claim 1

A signal processing device comprising: a charge transfer device including a charge transfer section composed of a plurality of transfer electrodes formed through a gate insulating film on a surface of a semiconductor substrate and arranged in file form of a column, a final transfer gate located adjacent to an output end of said charge transfer section, an output gate located adjacent to said final transfer gate, and an electric charge detection means located adjacent to said output gate; and a driving circuit including a reference signal generating circuit for generating a reference signal, a transfer clock generating circuit receiving said reference signal for generating a transfer clock to said charge transfer section, a digital counter of N bits receiving and counting said reference signal, a voltage generating means for generating a voltage starting to change only in a voltage decreasing direction in synchronism with the start of a counting operation of said counter, said voltage being applied to one of said final transfer gate and said output gate, and a latch for latching an output of said counter when an output of said electric charge detection means reaches a predetermined level, whereby said latch outputs a digital signal of N bits corresponding to a signal electric charge outputted from said charge transfer section.