US 4,104,543 AGranted

Multichannel CCD signal subtraction system

AssigneeHughes Aircraft Company

InventorDale G. Maeding

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Abstract

Signal charges in two charge coupled device (CCD) registers are subtracted one from the other by alternately passing them under a common, periodically clamped, normally floating sensing electrode. During those periods when the electrode is clamped, charge is shifted from the subtrahend register to the substrate region underlying the sensing electrode and charge, which has been shifted there previously from the minuend register, is shifted out of that region. During the intervening time periods, when the sensing electrode floats, the process is reversed, with charge from the minuend register being shifted under the sensing electrode and charge previously shifted there from the subtrahend register being shifted out. The resulting voltage reached by the sensing electrode during its floating intervals represents the difference between the charges in the two registers.

Claims6

Dependent claims

A method of subtracting a first signal from a second signal comprising the steps of:

(a) providing, in a semiconducting substrate first and second individual charge flow channels, extending first and second sets of charge transfer electrodes over respective ones of said channels, and extending an equipotential electrode structure over both of said channels;
(b) generating first and second pulse trains corresponding to the amplitudes of said first and second signals and applying said first and second pulse trains respectively to said first and second charge transfer electrodes;
(c) alternately clamping said electrode structure by connecting said structure to a source of clamping potential and floating said electrode structure by disconnecting said structure from said source of clamping potential;
(d) alternately stepping first and second trains of charge packets corresponding to said first and second pulse trains along said first and second charge flow channels respectively, into and out of the substrate region under said equipotential electrode structure so that each time said electrode structure is clamped, charge is shifted under it from one of said channels and each time it floats, charge is shifted under it from the other of said channels;
and
(e) detecting the potential of said electrode structure when it floats.

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Dependencies are inferred from the claim text.