Gray-to-Binary Converter Circuit for Low-Noise CMOS Image Sensors

The patent divides the ADC system into multiple column ADCs, each handling a specific column of pixel signals. This segmentation allows parallel processing of multiple columns simultaneously, achieving high conversion speed without requiring a single high-speed ADC that would consume excessive power. Each column ADC operates at a moderate speed, reducing individual power consumption while maintaining overall high throughput through parallel operation.

The patent replaces electromechanical switches with transistor-based switching circuits in the code conversion process. This substitution eliminates the mechanical contact noise inherent in traditional electromechanical switches while maintaining the switching functionality required for gray code to binary code conversion. The transistor-based implementation provides noise-free signal switching essential for high-quality image sensor operation.

The patent implements preliminary correlated double sampling (CDS) before the gray code to binary code conversion. This preliminary action captures and stores the pixel signals in a first memory, allowing subsequent subtraction of reference signals to remove noise components. By performing noise reduction before the code conversion, the system achieves both efficient parallel conversion and effective noise reduction, as the conversion operates on already-conditioned signals.