CMOS Image Sensor Data Readout with Dual Precharge
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Solution Overview
Problem
High-speed data readout in image sensors often conflicts with low power consumption, and existing column-parallel architectures face challenges in integrating analog-to-digital converters due to high resolution and parasitic RC loads, limiting the voltage swing margin of sense amplifiers.
Innovation Solution
A dual precharge scheme is implemented in a data readout apparatus, using a counter array with address decoders and sense amplifiers, where precharge circuits are placed on both sides of the counter array to increase the voltage swing margin and reduce parasitic RC loads, thereby enhancing data readout speed and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a column-parallel architecture with single-slope ADC is used, then high-speed readout is achieved, but the voltage swing margin of sense amplifiers is limited due to parasitic RC loads
Solution Approach 1:
The patent divides the counter array into multiple segments and places precharge circuits at different locations (both sides of the counter array) rather than using a single centralized precharge circuit. This segmentation reduces the parasitic RC load on each sense amplifier by distributing the precharge function across multiple locations, thereby increasing the voltage swing margin while maintaining high-speed readout capability
2Productivity
If high-resolution ADCs are integrated in column-parallel architecture, then data readout speed is improved, but parasitic RC loads increase, limiting sense amplifier performance
Solution Approach 1:
The patent introduces precharge circuits as intermediary elements between the counter array and the sense amplifiers. These precharge circuits actively compensate for the parasitic RC loads generated by high-resolution ADC integration, maintaining signal integrity and voltage swing margin without sacrificing data readout speed
3Object-affected harmful factors
If more channels are used for data readout, then voltage swing margin is improved, but device area and power consumption increase
Solution Approach 1:
Instead of increasing the number of channels (one-dimensional approach) to improve voltage swing margin, the patent transitions to a two-dimensional approach by placing precharge circuits at both sides of the counter array. This spatial distribution in multiple dimensions achieves improved voltage swing margin without proportionally increasing device area or power consumption
Data Source
AI summary
A data readout apparatus may include a counter array including an address decoder and a counter circuit, the address decoder being configured to receive an address, the counter circuit being coupled to the address decoder and perform a counting operation based on a column address, a sense amplifier array coupled to the counter array to read out the data from the counter array, a clock driver arranged adjacent to the center of the counter array to distribute clock pulses, a first precharge circuit arranged at one side of the counter array and structured to receive the clock pulses from the clock driver and perform a precharge operation, and a second precharge circuit arranged at the other side of the counter array and structured to receive the clock pulses from the clock driver and perform the precharge operation.