CMOS Image Sensor Readout Speed via Preliminary Reset
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Solution Overview
Problem
The Correlative Double Sampling (CDS) method for image sensors halves the frame rate due to the need to read out all pixels twice, limiting high-speed detection of particles or photons, which is inadequate for applications requiring fast read-out speeds.
Innovation Solution
A method that involves reading the pixel voltage three times, with no reset occurring between the second and third readings, allowing for pair-wise subtraction of read-out values to determine signals, reducing the number of required read-out cycles and increasing frame rate without performance loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Correlative Double Sampling (CDS) method is used to reduce noise, then measurement precision is improved, but productivity deteriorates due to halved frame rate
Solution Approach 1:
The patent applies preliminary action by performing the first read-out (reset level measurement) only once at the beginning of a sequence of M read-outs, rather than before every read-out. This preliminary reset level acquisition allows subsequent signal calculations to use this pre-acquired baseline, eliminating the need for repeated reset operations and thereby maintaining noise reduction performance while increasing frame rate by a factor of approximately M/2.
2Measurement precision
If all pixels are read out twice for CDS, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent performs the reset level measurement as a preliminary action that serves multiple subsequent read-outs. By acquiring the reset level once and reusing it for M different signal measurements, the method eliminates the need to spend read-out time performing reset operations before each measurement, thus reducing total read-out time while maintaining the ability to calculate accurate signals with noise reduction.
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 method enhances read-out speed by reducing the number of read-out cycles from 2M to M+1, enabling higher frame rates suitable for particle detection and maintaining performance equivalent to CDS, particularly valuable for detecting low-flux particles like neutrons, positrons, and X-rays.
Implementation Method 1
Each of these pixels can be selectively connected to an Analogue-to-Digital Convertor (ADC), and the voltage over the pixel is digitized. The voltage over the pixels is a result of impinging radiation, such as light.
Data Source
AI summary
To avoid reset noise in a CMOS chip for direct particle counting, it is known to use Correlative Double Sampling: for each signal value, the pixel is sampled twice: once directly after reset and once after an integration time. The signal is then determined by subtracting the reset value from the later acquired value, and the pixel is reset again. In some embodiments of the invention, the pixel is reset only after a large number of read-outs. Applicants realized that typically a large number of events, typically approximately 10, are needed to cause a full pixel. By either resetting after a large number of images, or when one pixel of the image shows a signal above a predetermined value (for example 0.8× the full-well capacity), the image speed can be almost doubled compared to the prior art method, using a reset after acquiring a signal.