TOF Macro-Pixel CMOS Readout for Faster 3D Distance Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing CMOS image sensors for time-of-flight (TOF) distance sensors and 3D cameras face limitations due to large pixel size, leading to slower charge transfer and worse distance resolution, along with increased design complexity and power consumption when averaging multiple pixels.
Innovation Solution
An array of pinned photodiodes (PPDs) interconnected to form macro-pixels, sharing a common sense node, with integrated transistors and switched capacitor circuits for correlated double sampling, enabling simultaneous charge transfer and low-noise signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large pixel size is used to accumulate sufficient photo-electrons, then signal strength is improved, but charge transfer speed decreases and distance resolution worsens
Solution Approach 1:
The patent divides the pixel array into groups where multiple pixels share a common sense node. This segmentation allows charge to be accumulated across multiple photodiodes but transferred through a shared node, maintaining fast transfer speed while accumulating sufficient signal charge from multiple pixels simultaneously.
Solution Approach 2:
Multiple pixels are merged to share a common sense node and readout circuitry. This combining approach allows the system to accumulate photo-electrons from multiple pixels (improving signal strength) while using a single fast transfer path (maintaining charge transfer speed), thus resolving the contradiction between signal accumulation and transfer speed.
2Measurement precision
If multiple pixels are averaged to improve signal, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
Multiple pixels are merged to share common sense nodes, transfer gates, and readout circuitry. This merging provides signal averaging capability (improving measurement precision) while eliminating the need for separate processing chains for each pixel, thereby reducing overall device complexity and power consumption compared to independent pixel processing.
Solution Approach 2:
The common sense node and readout circuitry serve multiple pixels simultaneously, providing a universal processing path that improves measurement precision through signal integration while avoiding the complexity of dedicated processing for each pixel. The same circuitry handles signals from multiple pixels, reducing overall system complexity.
3Measurement precision
If multiple pixels are averaged to improve signal, then measurement precision is improved, but power consumption increases
Solution Approach 1:
Multiple pixels share common sense nodes, transfer gates, and readout amplifiers. This merging allows the system to achieve signal averaging (improving measurement precision) while using a single set of power-consuming components for multiple pixels, thereby reducing total power consumption compared to having separate processing chains for each pixel.
Solution Approach 2:
The shared sense nodes and readout circuitry provide universal signal processing capability for multiple pixels. This multi-functionality allows the same power-consuming components to serve multiple pixels simultaneously, reducing overall power consumption while maintaining the measurement precision benefits of signal integration from multiple pixels.
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
The solution enhances distance resolution and reduces power consumption by allowing simultaneous charge transfer across multiple pixels, improving performance in portable devices without increasing response time.
Implementation Method 1
an array of photosensitive pixels... in which at least a subset of the pixels are interconnected to form a macro-pixel
Data Source
AI summary
A Time-of-flight optical device and a 3D optical detector comprising a CMOS integrated circuit with an array of photosensitive pixels that are, at least in part, interconnected to form macro-pixels (180). Each macro-pixel (180) groups a plurality of individual pixels contributing their photocarriers to a common sense node SN through a plurality of transistors in parallel. Preferably the integrated circuit includes switched capacitor circuits arranged to combine the potential of the sense nodes SN of a plurality of macro-pixels, and/or to perform correlated double samplings in an energy efficient way. Each pixel has now an additional sink gate (194) between the pinned photodetector, PPD, potential well and a positive voltage source. By this additional sink gate (194), the storage well of the PPDs can be emptied without transferring the charge to the sense node. The value of the transfer gate voltage V_TG may be adapted such that the potential barrier is not lowered all the way down, but decreased to a value VB<VP. In this manner, the potential well of the PPDs is emptied only in part. This amounts to subtracting a constant value from VTRAN and can be used to zero a background illumination value. Importantly, the charge left in the potential well is discharged by the sink transistor (194) before the next integration and does not affect successive cycles.