Solid-state image pickup device and clamp control method therefor

A solid-state image pickup device comprising:

• an image sensor having a black reference signal during at least one of a vertical blanking period and a horizontal blanking period;
• a correlated double sampling circuit for removing noises from the output signal from the image sensor;
• again control amplifier for amplifying the output signal of the correlated double sampling circuit;
• and
• a clamp circuit for making the output value of the gain control amplifier corresponding to the period of the blank reference signal coincident with a predetermined reference value, wherein said clamp circuit comprises:
• a feedback loop for performing feedback control on said gain control amplifier on the basis of the output signal;
• operating means for comparing the output signal output to said feedback loop with a reference value and outputting a clamp signal;
• a switch for opening/closing said feedback loop in accordance with the period of the black reference signal, and has at least one node connected to a first capacitance element to suppress voltage variation during a period other than a feedback clamp period so that the node concerned is prevented from being kept under a floating state out of the clamp period.

A clamp control method for a solid-state image pickup device comprising:

• an image sensor having a black reference signal during at least one of a vertical blanking period and a horizontal blanking period,
• a correlated double sampling circuit for removing noises from the output signal from the image sensor,
• a gain control amplifier for amplifying the output signal of the correlated double sampling circuit, and
• a clamp circuit for making the output value of the gain control amplifier corresponding to the period of the blank reference signal coincident with a predetermined reference value, the clamp circuit having a feedback loop for performing feedback control on the gain control amplifier on the basis of the output signal, operating means for comparing the output signal output to the feedback loop with the reference value and outputting a clamp signal, a switch for opening/closing the feedback loop in accordance with the period of the black reference signal, and gain control means for controlling the gain of the clamp signal supplied to the gain control amplifier, wherein the gain of the clamp signal supplied to the gain control amplifier is controlled by another gain control means different from the operating means.