Time of Flight Pixel Oversampling for Depth Precision
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Solution Overview
Problem
Current 3D image acquisition systems face challenges in achieving real-time processing due to sensitivity to noise, jitter, and the need for quick response times, especially when detecting reflected light from objects, which can be affected by undetected photons and complex triangulation techniques.
Innovation Solution
A time of flight sensing system that oversamples multiple measurements and uses adjustable frequency light pulses to compensate for noise and undetected photons, allowing for increased resolution and accurate depth determination by accumulating and scaling voltage measurements on capacitors within time of flight pixel cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measurements are taken to improve measurement precision, then measurement precision is improved, but response time increases
Solution Approach 1:
The system performs preliminary actions by accumulating multiple voltage measurements on capacitors before final depth calculation. The pixel cells accumulate oversampled measurements during the integration period, preparing the data in advance so that the final depth determination can be made quickly with high precision without requiring post-acquisition processing time.
Solution Approach 2:
The system uses periodic light pulses emitted at adjustable frequencies to illuminate the scene. By synchronizing the measurement accumulation with these periodic pulses, the system can take multiple measurements at regular intervals and combine them, achieving high precision depth measurement while maintaining a controlled response time through the periodic measurement rhythm.
2Measurement precision
If higher resolution depth measurement is achieved through multiple measurements, then measurement precision is improved, but sensitivity to noise and jitter increases
Solution Approach 1:
The system merges multiple individual voltage measurements taken from the same pixel cell into a single accumulated voltage value on a capacitor. By combining these measurements through accumulation, the random noise and jitter present in individual measurements are averaged out, resulting in a more precise depth measurement with reduced sensitivity to these harmful factors.
Solution Approach 2:
The system uses feedback by continuously monitoring the accumulated voltage measurements and using this information to determine the final depth value. The accumulation process itself provides a form of feedback where each new measurement is integrated with previous measurements, allowing the system to correct for noise and jitter through the cumulative effect of multiple samples.
3Productivity
If real-time processing is implemented with quick response times, then productivity is improved, but measurement precision deteriorates due to noise and jitter
Solution Approach 1:
The system performs preliminary measurement accumulation during the integration period, gathering multiple voltage samples in advance before the final depth calculation is required. This preliminary action allows the system to prepare high-precision measurement data during the available time window, enabling quick response when the depth value is needed for real-time processing without sacrificing measurement precision.
Solution Approach 2:
The system maintains continuous useful action by constantly accumulating measurements on the capacitors throughout the integration period. This continuous accumulation ensures that measurement gathering is ongoing and uninterrupted, maximizing the use of available time for data collection while maintaining precision, and allowing the system to quickly output results as soon as the integration period ends.
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 the system to distinguish slight depth differences and compensate for inaccuracies caused by undetected photons, improving the accuracy and reliability of real-time 3D image acquisition.
Implementation Method 1
In typical time of flight sensors, photodiodes are often used because of the high transfer efficiency from the photo detection regions to the sensing nodes.
Implementation Method 2
accumulating and scaling voltage measurements on capacitors within time of flight pixel cells
Data Source
AI summary
A time of flight pixel cell includes a photosensor to sense photons reflected from an object. Pixel support circuitry including charging control logic is coupled to the photosensor to detect when the photosensor senses the photons reflected from the object, and coupled to receive timing signals representative of when light pulses are emitted from a light source. A controllable current source is coupled to receive a time of flight signal form the charging control logic to provide a charge current when a light pulse emitted from the light source until the photosensor senses a respective one of the photons reflected from the object. A capacitor is coupled to receive the charge current, and a voltage on the capacitor is representative of a round trip distance to the object. A reset circuit is coupled to reset the voltage on the capacitor after being charged a plurality number of times.