Ping-Pong Image Sensor Readout With Dual Pixel Supplies
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern image sensors with high pixel counts face challenges in achieving high frame rates, low read noise, and high dynamic range while minimizing power consumption, leading to increased battery drain and thermal issues, as well as substantial die area and cost due to the large number of analog-to-digital converters (ADCs) required for readout.
Innovation Solution
The implementation of a ping-pong readout architecture with multiplexing circuitry and dual voltage supplies for pixel clusters, allowing ADCs to alternate between pixel columns and reduce power consumption and cross-talk, while maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large number of ADCs are used to read out high pixel count arrays, then readout speed and frame rate are improved, but die area and manufacturing cost increase substantially
Solution Approach 1:
Multiple ADCs are merged into a single ADC through time-multiplexed operation. The single ADC alternates between converting signals from different pixel clusters in successive frames, effectively combining the functionality of multiple ADCs into one physical device, thereby reducing die area while maintaining readout capability
Solution Approach 2:
The ADC operates in periodic alternating fashion between different pixel clusters. In even frames, it processes cluster A; in odd frames, it processes cluster B. This periodic time-division multiplexing allows a single ADC to handle multiple pixel clusters sequentially, reducing the total number of ADCs needed
2Measurement precision
If higher power is supplied to ADCs, then read noise decreases and dynamic range increases, but power consumption increases leading to shorter battery life and thermal heating
Solution Approach 1:
The patent merges the signal processing load of multiple pixel clusters into a single ADC, allowing the ADC to operate at lower power levels. By processing one cluster at a time with sufficient settling time, the ADC achieves low read noise without requiring the high simultaneous power that would be needed if multiple ADCs operated in parallel
Solution Approach 2:
The pixel clusters are pre-charged and settled during the transfer period before ADC conversion begins. This preliminary charging action ensures that the ADC receives fully prepared signals, allowing it to operate at lower power while still achieving low read noise performance
3Device complexity
If pixel clusters share common voltage supply, then device complexity is reduced, but cross-talk between adjacent pixels increases
Solution Approach 1:
The voltage supply system is segmented into separate supplies for different pixel clusters. Adjacent pixel clusters receive power from different voltage supplies, which prevents noise and cross-talk from propagating between clusters through the power distribution network, while maintaining manageable complexity through systematic segmentation
Data Source
AI summary
An image sensor includes a pixel array having a plurality pixels arranged in a plurality of pixel clusters coupled to a plurality of column busses, a plurality of voltage supplies coupled to the plurality of pixel clusters, and ping-pong readout circuitry. Pixel clusters in adjacent column busses are supplied with different voltage supplies. The ping-pong readout circuitry includes multiplexing circuitry coupled to the plurality of column busses, and a plurality of analog-to-digital converters coupled to the multiplexing circuitry. The image sensor also includes a controller configured to selectively couple a pixel signal of a pixel cluster to a column bus to an ADC for signal conversion.