Ramp Generator Buffer Layout for Uniform Pixel Column Conversion
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Solution Overview
Problem
In solid-state imaging devices, the use of a single ramp generator circuit results in varying voltage ramp signals at comparator inputs due to different RC parasitics across pixel columns, leading to inconsistent digital pixel values for the same light intensity.
Innovation Solution
The implementation of a ramp generator circuit with a resistor network and buffer circuits, where the output is divided into identical parts, ensures uniform voltage ramp signals across comparator inputs by minimizing the distance differences between buffer circuits and comparator circuits, thereby reducing RC parasitics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single ramp generator circuit is used for all pixel columns, then device complexity is reduced, but measurement precision deteriorates due to varying RC parasitics causing inconsistent voltage ramp signals
Solution Approach 1:
The ramp generator circuit is segmented into multiple independent ramp generator units, each serving a specific pixel column. This segmentation eliminates the common RC parasitic issue affecting all columns by providing dedicated voltage ramp generation for each column, thereby improving measurement precision without significantly increasing overall system complexity.
Solution Approach 2:
Each pixel column is provided with locally optimized ramp generator characteristics through dedicated circuitry. The local quality principle allows each column to have its own ramp signal generation with minimized local RC parasitics, ensuring consistent voltage ramp signals across all columns while maintaining manageable device complexity through modular design.
2Ease of manufacture
If buffer circuits are placed far from comparator circuits to simplify routing, then ease of manufacture improves, but measurement precision deteriorates due to increased RC parasitics
Solution Approach 1:
Buffer circuits are strategically positioned close to comparator circuits in the circuit layout design, performing the preliminary action of signal buffering before the signal reaches the comparator. This preliminary positioning minimizes the length of interconnect lines and reduces RC parasitics, ensuring voltage ramp signal uniformity while maintaining ease of manufacture through systematic layout planning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves more uniform radiation conversion across pixel columns, particularly in high dynamic range imaging devices, ensuring consistent digital pixel values for varying light intensities.
Implementation Method 1
The different distances result in different RC parasitics on the conductive paths, so that the voltage ramp signals at the inputs of the comparator signals may differ from each other
Data Source
AI summary
Pixel circuits of a solid-state imaging device are arranged in pixel columns, wherein, for each pixel column, signal outputs of the pixel circuits are connected to a data signal line. The solid-state imaging device further includes comparator circuits, wherein each comparator circuit generates an active comparator signal in response to a voltage difference between a first comparator input and a second comparator input. Each first comparator input is connected to one of the data signal lines. A ramp generator circuit includes at least one resistor network and buffer circuits. The ramp generator circuit generates a voltage ramp signal based on voltages at voltage tap nodes of the at least one resistor network. Each buffer circuit passes a buffered voltage ramp signal to the second comparator input of at least one of the comparator circuits.