Image Sensor Analog Binned Readout Phase Detection Autofocus
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Solution Overview
Problem
Current image sensors face challenges in enhancing their autofocus capabilities and power efficiency while maintaining high resolution and dynamic range, particularly in integrating phase detection autofocus pixels effectively within their architecture.
Innovation Solution
The integration of phase detection autofocus pixel circuits among image sensing pixel circuits in a color pixel array, utilizing buffer amplifiers with low threshold voltages and floating diffusion boost signals to dominate the output signals and enhance autofocus functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If phase detection autofocus pixels are integrated into the image sensor array, then autofocus capability is improved, but device complexity increases
Solution Approach 1:
The patent combines phase detection photodiodes and image sensing photodiodes into a shared pixel circuit architecture. Multiple photodiodes (including both PDAF and image sensing types) share common readout circuitry such as transfer transistors, floating diffusions, and source followers, allowing autofocus functionality to be integrated without proportionally increasing overall device complexity
Solution Approach 2:
The pixel circuit is designed to perform multiple functions: it can detect phase information from PDAF photodiodes for autofocus, capture image light from image sensing photodiodes for imaging, and route signals through shared readout paths. This multi-functional design allows a single circuit structure to serve both autofocus and imaging purposes
2Measurement precision
If analog binning is implemented to improve signal-to-noise ratio, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements analog binning by combining signals from multiple photodiodes (both PDAF and image sensing) through shared readout circuitry before digital conversion. Multiple photodiode outputs are summed in the analog domain through common floating diffusion nodes, improving signal-to-noise ratio while avoiding the need for separate processing circuits for each photodiode
Solution Approach 2:
The shared readout circuitry serves dual purposes: it performs analog binning to improve signal-to-noise ratio while simultaneously enabling phase detection functionality. The same transfer transistors, floating diffusions, and source followers that enable multifunctional operation also facilitate analog signal combining, achieving measurement precision improvement without proportional complexity increase
3Adaptability or versatility
If buffer amplifiers with low threshold voltages are used to dominate output signals, then autofocus functionality is improved, but use of energy increases
Solution Approach 1:
The patent employs buffer amplifiers with specifically engineered low threshold voltages to enhance the output signal from phase detection photodiodes. By adjusting the threshold voltage parameter of the buffer amplifier, the circuit prioritizes PDAF signal dominance over image sensing signals, improving autofocus functionality through electrical parameter optimization rather than additional circuitry
Solution Approach 2:
The low threshold voltage buffer amplifiers are strategically positioned only where needed to amplify phase detection signals, specifically in the signal path of PDAF photodiodes. This localized application of the low threshold voltage characteristic ensures autofocus signal dominance without requiring all buffer amplifiers in the array to consume additional energy, thus limiting the energy increase to specific regions
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 enables improved autofocus operations and efficient power management, allowing for enhanced image acquisition and processing capabilities while maintaining high resolution and dynamic range.
Implementation Method 1
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
An imaging device includes a first pixel circuit having a first plurality of photodiodes that includes a phase detection autofocus photodiode with image sensing photodiodes. A first buffer transistor having a first threshold voltage is coupled to the first plurality of photodiodes to generate a first output signal. A second pixel circuit is included having a second plurality of photodiodes that are all image sensing photodiodes. A second buffer transistor having a second threshold voltage is coupled to the second plurality of photodiodes to generate a second output signal. The first threshold voltage is less than the second threshold voltage. A driver is coupled to receive a combination of the first and second output signals to generate a total output signal. An influence of the first output signal dominates the second output signal in the total output signal because the first threshold voltage is less than the second threshold voltage.