Time-of-Flight Pixel Circuit Sharing Readout for Miniaturization
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Solution Overview
Problem
Conventional time-of-flight sensors face challenges with low photosensitivity and large size due to the need for multiple transistor devices to collect photoelectric phase signals, which occupies significant pixel area and hinders miniaturization.
Innovation Solution
A pixel circuit configuration that uses four charge storage and transfer circuits to modulate and generate integrated charge signals for different phases of a modulated light wave, with adjacent pixel cells sharing a charge readout circuit to reduce size and increase photosensitive area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple transistor devices are used to collect photoelectric phase signals, then measurement precision is improved, but device area increases
Solution Approach 1:
The pixel array is divided into multiple pixel cells, each responsible for collecting photoelectric phase signals at specific spatial positions. By segmenting the measurement function across multiple pixels, each pixel can use fewer transistor devices while the collective array maintains high measurement precision through spatial multiplexing of the four-phase signal collection.
Solution Approach 2:
The patent transitions from collecting all four phase signals within a single pixel to distributing phase signal collection across multiple pixels in the spatial dimension. Each pixel collects signals for specific phases, and the complete set of four-phase signals is reconstructed by combining outputs from multiple pixel cells, thereby reducing in-pixel transistor count while preserving measurement precision.
2Measurement precision
If multiple transistor devices are used to modulate and store photoelectric charge signals, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Each pixel cell is designed to perform multiple functions using a standardized set of transistor devices. The same transistor configuration in each pixel cell handles both modulation and storage of photoelectric charge signals for its assigned phases, eliminating the need for separate dedicated circuits and reducing overall device complexity while maintaining measurement precision.
Solution Approach 2:
The patent changes the operational parameters of the transistor devices, specifically using dual-gate transistor configurations where the first gate controls signal modulation and the second gate controls signal storage and transfer. This parameter-based control allows a single transistor device to perform multiple functions that would traditionally require separate devices, thereby reducing complexity while preserving precision.
3Measurement precision
If more pixel area is allocated to transistor devices, then measurement precision is improved, but photosensitive area decreases
Solution Approach 1:
The photoelectric signal processing function is segmented across multiple pixel cells in the array. Each pixel cell processes a subset of the four-phase signals, requiring fewer transistors per cell and thus leaving more area available for the photosensitive region in each cell, while the collective array maintains full measurement precision through distributed processing.
Solution Approach 2:
The patent moves signal processing functions from the intra-pixel dimension to the inter-pixel dimension. By distributing the four-phase signal collection across multiple pixels spatially, each pixel can be minimized in size with a larger photosensitive area, while the array as a whole maintains the capability for precise four-phase measurement through coordinated signal collection and processing.
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 photosensitivity and reduces the size of the pixel circuit, allowing for improved collection of time-of-flight data while maintaining or increasing the photosensitive area.
Implementation Method 1
a photoelectric conversion element configured to receive a modulated light wave to generate a charge
Data Source
AI summary
A pixel circuit of a time-of-flight sensor is disclosed, in the pixel cell in the Mth row and the Nth column, the photoelectric conversion element receives a modulated light wave to generate charges; the first charge storage and transfer circuit, the second charge storage and transfer circuit, the third charge storage and transfer circuit and the fourth charge storage and transfer circuit selectively modulates charges corresponding to four phases of the modulated light wave to generate four integrated charge signals according to four charge modulation signals, and outputs four integrated charge signals according to four control signals; the charge readout circuit outputs a third photoelectric signal and a second photoelectric signal according to the third integrated charge signal and the second integrated charge signal. Thus, the left and right pixel cells which are adjacent to each other share the charge readout circuit, the size of the pixel circuit is reduced.