Pixel Output Level Control Circuit for Image Sensor Offset Correction
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Solution Overview
Problem
Existing image sensors face challenges in improving noise characteristics and dynamic range of correlated double sampling circuits, particularly in correcting offsets in column signal lines and managing decision delays.
Innovation Solution
An apparatus with a level adjusting circuit that adjusts the voltage level of pixel signals in image sensors, using a current source and switching unit to correct offsets and improve dynamic range by generating a current based on a correction target value and applying it during correlated double sampling operations, and determining this value from digital pixel data from test patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a correlated double sampling circuit is used to improve noise characteristics, then noise performance is improved, but offset errors in column signal lines deteriorate measurement precision
Solution Approach 1:
The patent applies preliminary action by performing offset correction before the main signal measurement. A level adjusting circuit pre-adjusts the voltage level of pixel signals to correct offsets in column signal lines before the correlated double sampling operation. This preliminary correction ensures that subsequent measurements are not affected by offset errors, thereby improving both noise characteristics and measurement precision.
Solution Approach 2:
The patent introduces an intermediary element - a level adjusting circuit - that mediates between the pixel sensor output and the correlated double sampling circuit. This intermediary circuit adjusts the voltage level of incoming signals to compensate for offsets in the column signal lines, thereby improving measurement precision without compromising the noise rejection capability of the correlated double sampling circuit.
2Adaptability or versatility
If the dynamic range of correlated double sampling circuit is improved, then signal processing capability is enhanced, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the signal processing function into distinct segments: a level adjusting circuit for offset correction and a correlated double sampling circuit for noise rejection. This segmentation allows each circuit to be optimized for its specific function, improving dynamic range without requiring the entire system to become more complex. The level adjusting circuit handles offset correction independently, while the CDS circuit focuses on noise characteristics.
Solution Approach 2:
The patent utilizes parameter changes by adjusting the voltage level parameter of pixel signals through the level adjusting circuit. By changing the voltage level parameter to compensate for offsets, the circuit achieves improved dynamic range. The correction target value, determined from test pattern data, dynamically adjusts the voltage level parameter to optimize performance across different operating conditions without increasing fundamental circuit complexity.
3Measurement precision
If offset correction is performed in column signal lines, then measurement precision is improved, but additional circuit components increase device complexity
Solution Approach 1:
The patent applies merging by integrating the level adjusting circuit functionality into the existing pixel sensor readout path. The level adjusting circuit is combined with the column signal line structure, sharing common components such as signal lines and control logic. This merging approach enables offset correction without adding completely separate circuit components, thereby improving measurement precision while minimizing the increase in device complexity.
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
The solution effectively corrects offsets in column signal lines and enhances the dynamic range of correlated double sampling circuits, improving the accuracy and efficiency of image sensor operations.
Implementation Method 1
a current source configured to generate a current corresponding to a bias voltage based on the correction target value
Implementation Method 2
a switching unit configured to provide the generated current to the column signal line based on a switching control signal. The switching unit includes a transistor... The transistor is turned on in an interval associated with a correlated double sampling operation based on the switching control signal
Implementation Method 3
the pixel array is configured to convert an optical signal into a pixel signal and output the pixel signal to a column signal line; the at least one pixel sensor includes a photodetector
Data Source
AI summary
An apparatus for controlling a pixel output level includes a column signal line connected to an output node of at least one pixel sensor. The apparatus includes a load circuit is connected between the column signal line and a ground terminal. The apparatus also includes a level adjusting circuit configured to adjust a voltage level of a pixel signal output from the at least one pixel sensor to the column signal line based on a correction target value.