Image Sensor Frequency Controller Synchronizes Switching Regulator
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Solution Overview
Problem
Conventional image capturing apparatuses face challenges in reducing image noise caused by switching regulators, leading to S/N deterioration and horizontal stripes due to varying switching frequencies and readout cycles, which are not effectively addressed by existing methods.
Innovation Solution
An image capturing apparatus with a frequency controller that synchronizes the switching frequency of the switching regulator with the readout timings of the image sensor, ensuring a predetermined phase relationship between noise signal readout and signal readout operations to minimize noise differences across rows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching regulator operates at a fixed frequency, then the power supply is stable and simple to control, but switching noise interferes with image sensor readout causing horizontal stripes and S/N deterioration
Solution Approach 1:
The switching regulator transitions from fixed-frequency operation to variable-frequency operation, dynamically adjusting its switching frequency based on the image sensor's readout cycle to minimize noise interference while maintaining power supply functionality
Solution Approach 2:
The switching frequency parameter is changed and optimized to align with the readout cycle of the image sensor, specifically setting the switching frequency to 1/2 or 1/3 of the readout cycle frequency to reduce noise during critical readout periods
2Measurement precision
If the readout cycle is extended to reduce noise, then S/N ratio improves, but the readout speed decreases and productivity is reduced
Solution Approach 1:
The readout cycle parameter is optimized to balance noise reduction and readout speed, adjusting the cycle duration to achieve the best S/N ratio without excessively slowing down the readout process
Solution Approach 2:
The readout operation is structured as periodic action with optimized timing, performing readout at intervals that coincide with low-noise periods of the switching regulator, thereby achieving high S/N ratio while maintaining efficient data acquisition
3Object-affected harmful factors
If the switching frequency is changed to reduce noise, then horizontal stripes are reduced, but the control complexity increases
Solution Approach 1:
The switching frequency is adjusted to specific values (1/2 or 1/3 of readout cycle frequency) to eliminate horizontal stripe noise, with the control system managing the frequency transitions to minimize operational 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
This approach effectively reduces image noise and improves the accuracy of readout signals by uniformizing the potential levels during readout operations, thereby enhancing the signal-to-noise ratio and reducing horizontal-striped noise.
Implementation Method 1
an optical carrier generated in a photodiode (hereinafter, a PD) 401 accumulates in a gate electrode (a floating diffusion portion: a FD 411) of a MOS transistor. The potential change of the optical carrier is then amplified according to a drive timing signal from a scanning circuit, and the amplified potential change is output as a pixel signal.
Data Source
AI summary
An image capturing apparatus has an image sensor in which unit pixels each having a plurality of photoelectric conversion portions are arranged in matrix, a readout unit for performing a first readout operation of reading out signals of a portion of the plurality of photoelectric conversion portions and a second readout operation of reading out signals of a greater number of the plurality of photoelectric conversion portions, a switching regulator, and a frequency controller for controlling a switching frequency of the switching regulator. The frequency controller controls the switching frequency such that the phase of the switching frequency satisfies predetermined relationship, with respect to a timing for reading out noise signals, a timing for reading out signals by the first readout operation, and a timing for reading out signals by the second readout operation.