Charge coupled device provided with automatic bias-voltage setting means

Claim 1

A bias voltage setting circuit for a main charge coupled device, said main charge coupled device including a first input electrode, a plurality of gate electrodes and a first output electrode, all of said first input electrode, gate electrodes and first output electrode being formed on a single semiconductor substrate, said first input electrode being applied with an A.C. signal and a first D.C. bias voltage, each of said gate electrodes being applied with a pulse voltage, an electric charge not more than Q MAX being transferred from said first input electrode to said first output electrode through a channel formed under said gate electrodes, said first output electrode generating a signal voltage corresponding to the transferred electric charge, said bias voltage setting circuit comprising: (a) a first auxiliary charge coupled device including a second input electrode and a second output electrode each formed on said semiconductor substrate, said second input electrode being applied with a second D.C. bias voltage, an electric charge equal to Q MAX /n being detected by said second output electrode, where n is greater than one, said first auxiliary charge coupled device generating a first output voltage corresponding to said electric charge equal to Q MAX /n; (b) a first sample-hold circuit connected to said first auxiliary charge coupled device and applied with said first output voltage from said first auxiliary charge coupled device, for sampling and holding said first output voltage to generate a D.C. voltage V N ; (c) a second auxiliary charge coupled device including a third input electrode and a third output electrode each formed on said semiconductor substrate, said third input electrode being applied with a third D.C. bias voltage, said third output electrode generating a second output voltage in accordance with said third D.C. bias voltage; (d) a second sample-hold circuit connected to said second auxiliary charge coupled device and applied with said second output voltage from said second auxiliary charge coupled device, for sampling and holding said second output voltage to generate a D.C. voltage V X ; (e) a comparison circuit connected to said first and second sample-hold circuits and applied with said D.C. voltage V N from said first sample-hold circuit and said D.C. voltage V X from said second sample-hold circuit, for comparing said D.C. voltage V X with said D.C. voltage V N to generate a detection signal when said D.C. voltage V X is different from said D.C. voltage V N , said detection signal being supplied to said second auxiliary charge coupled device, to vary said third D.C. bias voltage so that said D.C. voltage V X becomes substantially equal to said D.C. voltage V N ; and (f) bias-voltage supply means connected between said third input electrode of said second auxiliary charge coupled device and said first input electrode of said main charge coupled device for supplying said third D.C. bias voltage of said third input electrode to said main charge couple device to use said third D.C. bias voltage as said first D.C. bias voltage of said first input electrode.