Preamplifier for low voltage signals in the presence of high voltage noise

Claim 1

An improved illumination detecting image sensing device comprising: a source of clock pulses; a solid state line scanner having a plurality of photodiodes, a clock pulse input connected to said source of clock pulses for scanning said photodiodes to produce a series of switched signals representative of the illumination level of said photodiodes, a video recharge gate terminal at which said series of switched signals appear, and a dummy recharge gate terminal for producing a series of switched signals independent of said illumination; an input resistor; a single-ended preamplifier having an input and an output with said input connected to said video recharge gate terminal through said input resistor; sample and hold means having a signal input, a signal output, and a timing input with said signal input connected to said output of said preamplifier to hold at its signal output a signal level corresponding to the level of the signal applied to said signal input at the time that a pulse is applied to said timing input; and delay means connected between said source of said clock pulses and said timing input of said sample and hold means to delay the sampling time of said sample and hold means until the signal from said preamplifier output has reached a maximum value.