Active Pixel Sensor Noise Reduction via Overlapping Sampling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Active pixel sensor (APS) imagers face significant noise interference from circuitry, which existing noise reduction techniques do not fully address, particularly in CMOS detectors, leading to suboptimal signal-to-noise ratios and image quality, especially in low light conditions.
Innovation Solution
The method involves placing an active pixel sensor in electrical contact with a column readout line and a sample-and-hold capacitor, which is also connected to an input capacitor on an amplifier, allowing simultaneous charging and reducing noise by overlapping the activation period, thus enhancing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional noise reduction techniques are used in CMOS APS imagers, then some noise is reduced, but signal-to-noise ratio remains suboptimal and image quality deteriorates in low light conditions
Solution Approach 1:
The patent applies preliminary action by performing correlated double sampling before the main signal readout. The circuit captures and stores the reset noise signal in a sample-and-hold capacitor during the reset phase, then subtracts this stored noise signal from the subsequent image signal, effectively removing the fixed pattern noise and kTC noise before the signal is amplified and processed further.
Solution Approach 2:
The patent introduces an intermediary sample-and-hold capacitor that temporarily stores the reset noise signal. This capacitor acts as a mediator between the reset phase and the readout phase, allowing the noise characteristics to be captured and later subtracted from the image signal, thereby isolating and removing the harmful noise components.
2Measurement precision
If multiple sampling circuits and reference voltages are used to reduce noise, then noise compensation is achieved, but device complexity increases
Solution Approach 1:
The patent merges the sample-and-hold functionality with the correlated double sampling circuitry. The same capacitor and switching network are used to perform both the sampling of the reset signal and the subsequent subtraction from the image signal, eliminating the need for separate dedicated circuits for each function and reducing overall device complexity.
Solution Approach 2:
The patent implements multi-functionality by designing the sampling circuit to serve multiple purposes: it captures the reset noise signal, stores it temporarily, and then enables its subtraction from the image signal. The same hardware components are reused across different operational phases, reducing the need for additional specialized circuits.
3Measurement precision
If sequential sampling of reset and image signals is performed, then noise from capacitance effects is compensated, but processing time increases
Solution Approach 1:
The patent employs periodic action by implementing a repeating cycle of reset sampling followed by image signal sampling. The circuit alternates between capturing the reset noise signal and capturing the image signal in a systematic periodic sequence, allowing efficient time-multiplexed operation that minimizes total processing time while achieving complete noise compensation.
Solution Approach 2:
The patent maintains continuity of useful action by overlapping the reset sampling and image signal sampling operations. The sample-and-hold capacitor continuously operates, capturing the reset signal in one phase and immediately transitioning to capture the image signal in the next phase, eliminating idle time and ensuring continuous productive operation of the circuit.
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 improves the signal-to-noise ratio, resulting in better image quality under various ambient conditions, including low light, by minimizing noise attenuation and parasitic capacitance effects.
Implementation Method 1
placing a sample-and-hold capacitor into electrical contact with the column readout line, and placing the sample-and-hold capacitor in electrical contact with an input capacitor on an amplifier
Data Source
AI summary
In accordance with an exemplary embodiment of the present invention, a method is provided to form an image using an active pixel sensor imager (108). The method includes placing an active pixel sensor (202) in electrical contact with a column readout line (204), lacing a sample-and-hold capacitor into electrical contact with the column readout line, and placing the sample-and-hold capacitor (314 or 320) in electrical contact with an input capacitor (324 or 334) on an amplifier (222). All of the input capacitor (324 or 334), the sample-and-hold capacitor (314 or 320), and the active pixel sensor (202) are in electrical contact for an overlapping period of time. A differential output (228) from the amplifier (222) is digitized, and used to form an image.