Image input system

Abstract

An image input system comprises a solid state image pickup device and a preprocessor (3) for performing correlated double sampling amplification on an output signal of the solid state image pickup device and outputting a video signal. The preprocessor comprises: a correlated double sampling amplifier (30) for outputting signal information corresponding to a difference voltage between the black level in a feedthrough period of the solid state image pickup device and a signal level in a charge signal output period; and offset cancelling means (38) for applying an offset cancelling voltage for cancelling an offset voltage corresponding to the difference voltage between the black level and the signal level in a state where the solid state image pickup device is optically interrupted to the input terminal of the correlated double sampling amplifier. The correlated double sampling amplifier cancels out the offset voltage and the offset cancelling voltage as signal components of polarities opposite to each other. Circuits at the post stage of the correlated double sampling amplifier are not influenced by the offset voltage. Even if capacitive noise characteristics of the solid state image pickup device are not preferable, a high-grade image can be inputted.

Description

[0001] This is a continuation application of U.S. Ser. No. 10 / 200,162, filed Jul. 23, 2002; which is a continuation application of U.S. Ser. No. 09 / 529,651, filed Apr. 18, 2000, now U.S. Pat. No. 6,499,663.TECHNICAL FIELD [0002] The present invention relates to an image input system for optically inputting an image by using a solid state image pickup device of an X-Y address system using MOS transistors, a solid state image pickup device of a charge transfer system using a CCD (Charge Coupled Device), or the like for photoelectric conversion and charging. More particularly, the invention relates to a technique of lessening an influence of noise components of a signal outputted from a solid state image pickup device, which is exerted on a process of a correlated double sampling method at a post stage or the like and relates to, for example, a technique which is effective when applied to a video camera, a digital still camera or the like. BACKGROUND ART [0003] A CCD can convert an opt...

AI Technical Summary

Benefits of technology

"The invention is an image input system that includes a solid state image pickup device and a preprocessor. The preprocessor includes a correlated double sampling amplifier and offset cancelling means for reducing noise in the image signal. The system also includes a data processor for processing the image signal. The offset cancelling means removes or reduces the offset voltage from the image signal obtained from the solid state image pickup device. The system can be used even when the quality of the image is not good. The offset cancelling means can be implemented using various modes and circuit configurations. The technical effect of the invention is to improve the quality of image input and reduce the control amount required for the image input system."

Problems solved by technology

Due to parasitic capacitance between the gate and source of the precharge MOS transistor and parasitic capacitance (output node parasitic capacitance) between the final transfer gate of the solid state image pickup device and the output node, when the outputting operation of the outputting unit shifts from the feedthrough period to the charge signal output period, a change in a pulse signal for controlling the charge transfer causes an undesirable change in the level of the output node via the output node parasite capacitance.

The inventors have found that since the capacitance of the floating capacitive element tends to be reduced in order to increase the detection sensitivity of the outputting unit, the output node parasite capacitance relatively increases and it causes an increase in the undesirable level change in the charge signal output period.

The undesirable level change due to the capacitive noise causes an undesirable offset voltage which is outputted from the source follower output circuit in the charge signal output period.

The inventors have found that when the offset voltage increases, the amount of the feedback control performed by the feedback clamping circuit increases and it is feared that the circuit operation cannot follow it.

When the feedback control cannot follow, the reference of the video signal changes at random on the horizontal scan unit basis and it causes unevenness in an input image.

When the conductance of transistors constructing the feedback clamping circuit is increased in order to deal with the problem, it brings about an increase in a chip occupying area and power consumption.

Especially, under the circumstances that the operation source voltage is decreased to realize low power consumption, the necessary feedback control amount cannot be satisfied.

When the preprocessor including the correlated double sampling amplifier and the feedback clamping circuit is provided as a preprocessing LSI formed as a semiconductor integrated circuit, the preprocessing LSI cannot be generally used for a solid state image pickup device having a relatively large capacitive noise component.

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