Saturday, January 30, 2021

Reference for Column-Parallel Sigma-Delta ADC

Ams and University of Madeira, Portugal, publish a MDPI paper "Reference Power Supply Connection Scheme for Low-Power CMOS Image Sensors Based on Incremental Sigma-Delta Converters" by Luis Miguel Carvalho Freitas and Fernando Morgado-Dias.

"Modern Complementary Metal-Oxide-Semiconductor (CMOS) image sensors, aimed to target low-noise and fast digital outputs, are fundamentally based on column-parallel structures, jointly designed with oversampling column converters. The typical choice for the employed column converters is the incremental sigma-delta structures, which intrinsically perform the correlated multiple sampling, creating an averaging effect over the system thermal noise when used in conjunction with 4T-pinned pixels. However, these types of column converters are known to be power-hungry, especially if the imaging device needs to target high frame rate levels as well. In this sense, the aim of this paper was to address the excess of power dissipation problem that arises from image sensors while employing oversampling high-order incremental converters, by means of using a different connection scheme to supply and to drive the required reference signals across the image sensor on-chip column converters. The proposed connection scheme revealed to be fully functional with no unwanted artifacts in the imager output response, allowing it to avoid 20% to 50% of the power dissipation, relative to the classical on-chip references generation and driving method. Furthermore, this solution allows for a much less complicated and less crowded printed circuit board (PCB) system."

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