Shared Readout Circuit for Image Pickup Element Focus Detection
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Solution Overview
Problem
In image pickup elements with pixel-parallel analog-to-digital conversion, the simultaneous readout of signals from multiple photoelectric converters for focus detection is hindered by timing differences, leading to decreased focus detection performance, especially with moving objects, and the increased circuit area required for additional AD converters.
Innovation Solution
The implementation of a shared readout circuit configuration where adjacent photoelectric converters in an image pickup element share readout circuits, ensuring synchronized signal storage timings without a significant increase in circuit area, allowing for efficient focus detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two AD converters are provided for each unit pixel to enable simultaneous readout of signals from multiple photoelectric converters for focus detection, then focus detection performance is improved, but circuit area increases significantly
Solution Approach 1:
The patent merges the readout functions by having adjacent unit pixels share readout circuits. Specifically, the first readout circuit reads out signals from the second photoelectric converter of the first unit pixel and the first photoelectric converter of the second unit pixel, while the second readout circuit reads out signals from the third photoelectric converter of the second unit pixel. This sharing arrangement reduces the total number of readout circuits needed while maintaining the capability for simultaneous signal readout required for focus detection
Solution Approach 2:
The readout circuits are designed to serve multiple functions and multiple photoelectric converters. Each readout circuit can read out signals from different photoelectric converters in different unit pixels, making the readout circuit universal. This multi-functionality allows the system to achieve focus detection capability without requiring a dedicated AD converter for each photoelectric converter, thereby reducing circuit area
2Area of stationary object
If a shared readout circuit is used between adjacent unit pixels, then circuit area is reduced, but the number of transistors per unit pixel decreases
Solution Approach 1:
The patent merges readout circuit resources between adjacent unit pixels. The first readout circuit is shared between the second photoelectric converter of the first unit pixel and the first photoelectric converter of the second unit pixel. This merging reduces the total transistor count while maintaining readout functionality across all photoelectric converters
Solution Approach 2:
The patent transitions from a one-to-one mapping between photoelectric converters and readout circuits to a many-to-one relationship. By organizing unit pixels in a two-dimensional array and having adjacent pixels share readout circuits, the system exploits spatial dimensionality to reduce circuit complexity. The cross-unit-pixel sharing creates a more efficient resource allocation that reduces overall transistor count
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 maintains the simultaneity of signal storage timings across photoelectric converters, enhancing focus detection accuracy for moving objects while minimizing the circuit area required for AD conversion, thus improving focus detection performance without increasing the number of circuits.
Implementation Method 1
a first photoelectric converter of a first pixel portion and a second photoelectric converter of a second pixel portion adjacent to the first pixel portion share a first readout circuit
Data Source
AI summary
An image pickup element has a configuration in which a pixel region substrate and a readout circuit substrate are stacked. On a pixel region substrate, a plurality of unit pixels configured by a micro lens and a plurality of photoelectric converters are arranged in the horizontal direction and the vertical direction. On a readout circuit substrate, a plurality of readout circuits that read out a signal based on charges stored in the photoelectric converter is arranged in the horizontal and vertical directions. In the unit pixels that are adjacent to each other in the horizontal direction (or the vertical direction), a first photoelectric converter of a first unit pixel and a second photoelectric converter of a second unit pixel share one readout circuit.