Image Sensor ADC Merging for TOF Area Reduction
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Solution Overview
Problem
Time-of-Flight (TOF) image sensors, particularly the indirect method, require separate analog-to-digital converters for each tap pixel signal, leading to increased space occupancy and complexity.
Innovation Solution
An image sensor design that analog-to-digital converts the voltage difference between pixel signals of two taps using an operational amplifier for auto-zeroing and comparison with a ramp voltage, and a counter circuit to generate a digital code, reducing the need for separate converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate analog-to-digital converters are used for each tap pixel signal in the indirect TOF method, then accurate distance measurement is achieved, but the space occupancy and device complexity increase significantly
Solution Approach 1:
The patent merges the analog-to-digital conversion functions for both tap A and tap B pixel signals into a single shared ADC. The operational amplifier sequentially processes signals from both taps through time-multiplexed auto-zeroing operations, allowing one ADC to perform conversions that would traditionally require two separate converters, thereby reducing the image sensor area while maintaining measurement accuracy
Solution Approach 2:
The operational amplifier is designed to perform multiple functions: it conducts auto-zeroing calibration for both tap A and tap B signals, performs analog-to-digital conversion for both taps, and manages sequential signal processing. This multi-functional design eliminates the need for dedicated converters for each tap, reducing overall device complexity and area occupancy
2Reliability
If separate analog-to-digital converters are used for each tap pixel signal, then independent signal processing is achieved, but the device complexity and space requirements increase
Solution Approach 1:
The patent combines multiple independent conversion functions into a unified ADC architecture. The operational amplifier sequentially handles auto-zeroing and conversion for both tap signals through time-multiplexed operation, reducing the number of independent converters from two to one while maintaining signal processing integrity through controlled sequential access
Solution Approach 2:
The operational amplifier performs periodic auto-zeroing calibration cycles for both tap A and tap B signals at predetermined intervals. This periodic calibration maintains signal processing independence and accuracy while using a single shared converter, thereby reducing device complexity compared to having continuously operating separate converters for each tap
Data Source
AI summary
An image sensor including a pixel of a first tap. a pixel of a second tap. an operational amplifier configured to perform an auto zeroing operation with a pixel signal of the pixel of the second tap applied, and perform an operation for comparison between a ramp voltage and a signal output from the pixel of the first tap, with a pixel signal of the pixel of the first tap applied, and a counter circuit configured to generate a digital code in response to an output of the operational amplifier.