High-speed and high-accuracy CMOS LSI for document image signal processor

A signal processing circuit was created on a one-chip CMOS LSI in which the document image is read by a line sensor and is converted to digital signals. The present LSI, which corrects various distortions contained in the image signals accurately at a high speed, can handle a high-speed image signal processing (with 5M picture elements/s maximum) and hence can be applied to an ultra-high-speed G4 facsimile. A high-speed operational amplifier and a high-speed comparator needed for one-chip realization are used. Especially, for improvement of accuracy of the CMOS operational amplifier, the automatic offset cancelling system has been developed so that the process of the analog input signal of several hundred millivolts from the sensor can be accomplished. In the present LSI, the CMOS process of 2.5 μm rule is used and the chip size is 6.8 × 7.5 mm.