Image Sensor Auto-Focusing Noise Reduction via Differential Signal Processing
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Solution Overview
Problem
Image sensors face saturation issues during auto-focusing, leading to inaccurate output due to noise amplification and potential errors in signal processing.
Innovation Solution
The image sensor design incorporates a pixel array with first and second photodiodes, transfer transistors, a ramp voltage generator, correlated double sampler, counter, and digital scaler, along with a gain controller to adjust gains for different operation modes, employing a reset-signal-signal (RSS) read-out scheme to reduce noise and prevent saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional auto-focusing signal processing is used, then processing speed is maintained, but saturation errors occur due to noise amplification
Solution Approach 1:
The patent applies preliminary action by performing signal differentiation and noise filtering before the auto-focusing calculation process. The signal processing unit differentiates the output signals from photodiodes and filters noise in advance, preventing noise amplification during subsequent gain application and correlation computation, thereby ensuring accurate auto-focusing without saturation errors.
2Measurement precision
If gain is increased to amplify weak signals, then signal-to-noise ratio improves, but saturation errors occur in auto-focusing
Solution Approach 1:
The patent extracts and processes only the differential component of the signal that contains auto-focusing information. By differentiating the output signals from multiple photodiodes and focusing computation on the difference signal, the system achieves accurate auto-focusing measurement without needing to amplify the entire signal, thereby avoiding saturation errors while maintaining measurement precision.
Solution Approach 2:
The patent applies different processing strategies to different signal components. Full gain amplification is applied to the sum signal for image brightness, while the differential signal for auto-focusing undergoes differentiation and noise filtering with reduced gain. This local quality approach ensures accurate auto-focusing measurement without saturation.
3Reliability
If signal processing complexity is increased to reduce noise, then auto-focusing accuracy improves, but power consumption increases
Solution Approach 1:
The patent performs noise-reducing differentiation and filtering operations in advance, before the main auto-focusing computation. By preparing cleaned differential signals upfront, the system reduces the computational burden and power consumption of subsequent processing stages while maintaining high auto-focusing accuracy.
Solution Approach 2:
The patent discards noise components through differentiation and filtering operations, keeping only the useful auto-focusing information in the differential signal. This selective retention of useful information while discarding noise reduces the amount of data requiring further processing, thereby lowering power consumption while maintaining accuracy.
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 configuration enhances image sensor performance by reducing noise amplification and preventing saturation errors, allowing for accurate auto-focusing and improved image quality without increasing power consumption or sensor area.
Implementation Method 1
Each of the pixels includes a photodiode (PD). The photodiode serves to convert incident light into an electrical signal.
Data Source
AI summary
Provided are image sensors. An image sensor includes a pixel array comprising pixels configured to output signal voltages, each of the pixels comprising first and second photodiodes, first and second transfer transistors connected to the first and second photodiodes, respectively, and a floating diffusion node to which the first and second transfer transistors are connected; a ramp voltage generator configured to generate a ramp voltage that decreases with a slope according to a ramp clock to have a first gain; a correlation double sampler (CDS) configured to compare the ramp voltage with the signal voltages to output a comparison signal; a counter configured to count the comparison signal according to a counter clock to output a digital signal; and a digital scaling unit configured to scale the digital signal to have a second gain.