Contact image sensor utilizing differential voltage pickoff

Claim 1

A contact image sensor circuit comprising: a plurality of active sensing elements, a plurality of dummy sensing elements, each said dummy sensing element is placed in close proximity to a corresponding active sensing element, a shielding means to ensure that said dummy sensing elements receive no light exposure so that each dummy sensing element generates a reference output signal, control and drive clocks to control the timing and scan advance of the circuit, a digital scanning shift register, a first buffer amplifier and a second buffer amplifier; wherein said active sensing elements are activated in sequence by said shift register, each said active sensing element thereby generating an output signal that is received in said first buffer amplifier, as said shift register activates each succeeding active sensing element in sequence, said shift register resets each preceding active sensing element in sequence to a dark level, said dummy sensing elements are sequentially activated in the same manner as are said active sensing elements, said reference output signals of said dummy sensing elements are received in said second buffer amplifier, said output signals from said active sensing elements are compared to said reference output signals of said dummy Sensing elements to scrub said output signals from said active sensing elements of dark fixed pattern noise and DC offset voltage, thereby generating a resultant video output signal.