Pixel Circuit Double Sampling for Signal Integrity
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Solution Overview
Problem
Current solid-state image sensing devices face challenges in efficiently converting light into electrical signals and transmitting these signals without interference, particularly in applications requiring minimal chip size and robust electromagnetic interference characteristics.
Innovation Solution
The proposed imaging system incorporates an array of pixel image sensors with a control circuit that generates reset, transfer, and initiation signals to activate photoelectron sensing devices, enabling double sampling and serial video output, and includes a pixel reference voltage generator to condition and amplify signals for external processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard CMOS processes are used to integrate signal processing functions with pixel arrays, then manufacturing complexity is reduced and ease of manufacture is improved, but chip size increases due to additional circuitry
Solution Approach 1:
The patent combines multiple functions (photoelectron sensing, signal amplification, double sampling, and serial output control) into a single integrated pixel circuit using standard CMOS processes. The source follower transistor serves both as a buffer and as part of the double sampling mechanism, while the gated power supply integrates timing control directly into the pixel, eliminating the need for separate external circuits and reducing overall chip size.
Solution Approach 2:
The pixel circuit is designed with multi-functionality: the source follower transistor acts as both a signal buffer and a sampling hold element, the floating diffusion node serves as both charge storage and signal amplification, and the gated power supply provides both power control and timing synchronization. This multi-functionality reduces the number of dedicated components needed, thereby reducing chip size while maintaining ease of manufacture using standard CMOS processes.
2Measurement precision
If double sampling is implemented to improve signal precision, then measurement precision is improved, but device complexity increases due to additional sampling circuits
Solution Approach 1:
The patent implements double sampling by merging the first sampling (reset level capture) and second sampling (signal level capture) operations within the same pixel circuit using the floating diffusion node and source follower transistor. The same hardware components perform both sampling functions at different time points, eliminating the need for separate sampling circuits and reducing device complexity while maintaining high signal precision through correlated double sampling.
Solution Approach 2:
The double sampling process uses periodic action with two distinct sampling phases: the first sampling occurs at the reset level, and the second sampling occurs at the signal level. These periodic sampling operations are controlled by timing signals from the gated power supply, allowing precise measurement of photoelectron signals while using the same hardware components repeatedly, thereby reducing device complexity.
3Area of stationary object
If serial video output is used to reduce the number of output lines, then chip size is reduced, but transmission speed decreases compared to parallel output
Solution Approach 1:
The patent implements continuous serial video output where pixels are read out sequentially row by row without interruption. The gated power supply ensures continuous timing control, and the column switches continuously transfer signals from each pixel to the single output line. This continuous operation maintains efficient data flow and compensates for the sequential nature of serial output, reducing chip size while maintaining acceptable transmission speed for the application.
4Area of stationary object
If minimal chip size is achieved by integrating all functions in-pixel, then area is reduced, but signal interference increases due to crowded circuit layout
Solution Approach 1:
The patent applies local quality by optimizing the spatial arrangement and electrical characteristics of components within each pixel. The source follower transistor is positioned to provide high impedance buffering that isolates the floating diffusion node from subsequent circuit stages. The gated power supply is locally controlled within each pixel to minimize cross-talk. This localized optimization of component placement and electrical properties reduces signal interference despite the compact in-pixel integration.
Solution Approach 2:
The source follower transistor acts as an intermediary element between the floating diffusion node (charge-to-voltage conversion) and the output circuitry. It provides high impedance buffering that isolates the sensitive charge storage node from loading effects and signal interference from subsequent stages. This intermediary function protects the photoelectron signal integrity while allowing compact integration of all circuit elements within the pixel.
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 solution allows for efficient light-to-electrical signal conversion and transmission of high-quality video signals with minimal chip size, maintaining signal integrity even in interference-prone environments, suitable for applications like medical endoscopy.
Implementation Method 1
Each photo sensor includes one picture element (pixel) of the image. Light energy emitted or reflected from an object impinges upon the array of photo sensors. The light energy is converted by the photo sensors to an electrical signal.
Data Source
AI summary
An imaging system provides a serial video signal that is indicative of the intensity of the light. The imaging system has an array of pixel image sensors arranged in rows and columns. A control circuit is in communication with the rows of the array and the plurality of column switches. The control circuit generates reset control signals, transfer gating signals, pixel image sensor initiation signals for each selected row for controlling resetting, integration of photoelectrons generated from the light impinging upon the array of pixel image sensors, charge transfer of the photoelectrons from the photosensing devices to the charge storage device, and to activate the photoelectron sensing devices on each row to generate output signals from each of the pixel image sensors on a selected row. The control circuit generates the column selection signals for transfer of the output signals from selected rows to form a serial video output signal.