Predictive Pre-Charging Circuitry for Image Sensor Readout
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Solution Overview
Problem
Conventional image sensors experience prolonged column readout operations due to the need for settling time when transitioning from reset voltage to signal voltage during correlated double sampling, which can be improved by reducing the voltage difference between the two.
Innovation Solution
The implementation of predictive pre-charge circuitry that pre-charges column output lines based on the voltages of previous image pixel rows, reducing the settling time required during readout operations by minimizing the difference between reset and signal voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional column readout operations are performed with correlated double sampling, then accurate image signal reading is achieved, but readout time is prolonged due to settling time requirements
Solution Approach 1:
The patent applies preliminary action by pre-charging the column output lines to a voltage level predicted from previous pixel row data before the actual readout operation begins. This predictive pre-charging reduces the voltage difference that would otherwise need to settle during correlated double sampling, thereby maintaining measurement precision while significantly reducing the readout time penalty associated with conventional settling procedures
2Measurement precision
If settling time is allowed to transition from reset voltage to signal voltage, then accurate voltage comparison is achieved, but overall readout speed is reduced
Solution Approach 1:
The patent changes the voltage parameter dynamically by using predictive pre-charging to set the output line voltage based on previous pixel data before the current row readout begins. This parameter change reduces the magnitude of voltage transition required during correlated double sampling, allowing faster settling while maintaining the accuracy needed for precise voltage comparison between reset and signal levels
Data Source
AI summary
An imaging device may have an array of image sensor pixels and image readout circuitry coupled to the array of image sensor pixels. Predictive pre-charge circuitry may be coupled to the array of image sensor pixels and the image readout circuitry. The predictive pre-charge circuitry and the image readout circuitry may perform correlated double sampling operations during charge readout, comparing the charge generated by the array of image pixels to a known reset value. The predictive pre-charge circuitry may pre-charge output lines from the array of image pixels, thereby reducing the time needed for the circuitry to read out the charge after being reset. The output lines may be pre-charged prior to reading out the charge of a row of image sensor pixels based on a voltage associated with the charge generated by at least one previous row of image sensor pixels of the array of image sensor pixels.