Adaptive Image Sensor Readout Circuit for CMS Noise-Speed Tradeoff
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Solution Overview
Problem
Conventional image sensors face challenges in reducing readout noise, particularly in dark conditions, and are inefficient in handling signal variations, leading to increased readout time and reduced frame rates due to the use of correlated multiple sampling (CMS) techniques.
Innovation Solution
An adaptive readout circuit that determines signal size using a comparator and performs either CMS or non-CMS calculations based on the signal strength, reducing readout periods by optimizing sampling methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correlated multiple sampling (CMS) is used to reduce readout noise, then signal-to-noise ratio is improved, but readout period increases and frame rate decreases
Solution Approach 1:
The patent implements adaptive CMS that dynamically adjusts the sampling method based on signal strength. When the signal is bright (above threshold), non-CMS is used for fast readout; when the signal is dark (below threshold), CMS is used to reduce noise. This dynamic adaptation resolves the contradiction by selecting the optimal method for each pixel's signal conditions.
Solution Approach 2:
The system changes the readout parameter (CMS enabled or disabled) based on the signal intensity parameter. By monitoring signal strength and adjusting the readout method parameter accordingly, the system achieves both high frame rate for bright signals and high signal-to-noise ratio for dark signals.
2Measurement precision
If correlated multiple sampling (CMS) is used to reduce readout noise, then readout noise is reduced, but readout time increases
Solution Approach 1:
The readout time is dynamically adjusted based on signal strength. For bright signals, the system uses non-CMS with shorter readout time; for dark signals, it uses CMS with longer readout time to reduce noise. This dynamic time adjustment resolves the contradiction between readout noise reduction and readout time.
Solution Approach 2:
The system changes the readout mode parameter based on signal intensity, switching between CMS (longer time, lower noise) and non-CMS (shorter time, higher noise) to optimize the time-noise tradeoff for each pixel.
3Productivity
If adaptive readout circuit is used to optimize sampling methods, then readout period is reduced, but device complexity increases
Solution Approach 1:
The patent applies different readout qualities locally to different pixels based on their signal strength. Each pixel receives the appropriate readout treatment (CMS or non-CMS) based on its local signal conditions, rather than applying a uniform readout method to the entire sensor array. This local adaptation reduces overall readout period while managing complexity.
Solution Approach 2:
The patent introduces a signal strength detection mechanism as an intermediary that determines whether CMS should be applied. This intermediary component automatically selects the appropriate readout method based on signal intensity, reducing the need for complex manual control while achieving optimized readout periods.
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 reduces readout periods by approximately 10% to 20% depending on the resolution, while preserving the benefits of CMS and improving signal-to-noise ratio, especially in bright conditions.
Implementation Method 1
A readout circuit includes a comparator having a first input coupled to receive an input signal and a second input coupled to receive a reference signal. The comparator is configured to generate a digital comparator output in response to a comparison of the input signal and the reference signal.
Data Source
AI summary
A readout circuit includes a comparator having a first input coupled to receive a ramp signal from a ramp generator and a second input coupled to receive an analog image data signal from one of a plurality of bitlines. The comparator is configured to generate a comparator output in response to a comparison of the ramp signal and the analog image data signal. A sampling circuit has a first input coupled to receive a sampling control signal and a second input coupled to receive the comparator output. The sampling circuit is configured to generate a sampling output. A counter has a first input coupled to receive a counter control signal and a second input coupled to receive one of the comparator output and a signal from the sampling circuit. The readout circuit is configured to perform correlated multiple sampling (CMS) calculations or non-CMS calculations in response to the sampling output.