Solid-state image pickup device and clamp control method therefor

Abstract

In an analog front end (FE) IC chip having a CDS (Correlated Double Sampling) function and an AGC (Automatic Gain Control) function, a clamp circuit for clamping an output signal during a black reference signal period is equipped with a mechanism for suppressing the effect of noises contaminated from a power source, external circuits, etc.

1 . A solid-state image pickup device comprising:
 a pixel unit outputting 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 an output signal of the pixel unit and outputting a correlated output signal;   a gain control amplifier for amplifying the output signal of the correlated double sampling circuit; and   a clamp circuit comprises:   a feedback loop for performing feedback control on said gain control amplifier on the basis of the output signal;   operating unit for comparing the gain adjusted output signal 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   gain control unit for controlling the gain of the clamp signal supplied to said gain control amplifier.   
     
     
         2 . The solid-state image pickup device as claimed in  claim 1 , wherein said correlated double sampling circuit, said gain control amplifier and at least said feedback loop, said switch and said gain control means of said clamp circuit are equipped in the same IC. 
     
     
         3 . The solid-state image pickup device as claimed in  claim 1 , wherein said gain control means comprises any one of a current-voltage converting circuit, a voltage-current converting circuit, a current-current converting circuit and a voltage-voltage converting circuit. 
     
     
         4 . The solid-state image pickup device as claimed in  claim 1 , wherein said gain control means supplies said gain control amplifier with a voltage value ΔVfb (ΔVfb<ΔVout) smaller than the voltage variation value ΔVout of the clamp signal based on said feedback loop. 
     
     
         5 .- 11 . (canceled)