Programmable Current Source for Time of Flight 3D Image Sensor
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Solution Overview
Problem
Time of flight 3D image sensors face accuracy and reliability issues due to pixel-by-pixel variations in current mirror outputs, which complicate real-time 3D image acquisition and are challenging for small device applications.
Innovation Solution
Implementing programmable current sources with a single reference current source across time of flight pixel cells, ensuring each pixel cell receives a substantially equal current, thereby minimizing variations and enhancing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If separate circuitry is coupled to photodiodes in each pixel cell to detect and measure reflected light, then real-time 3D image acquisition is enabled, but pixel-by-pixel variations in current mirror outputs occur, reducing accuracy and reliability
Solution Approach 1:
The patent merges the current reference source functionality into a single shared circuit that serves all pixel cells, rather than having separate circuitry in each pixel. This consolidation eliminates pixel-by-pixel variations in current mirror outputs while maintaining the real-time 3D image acquisition capability through the unified current reference distribution to all photodiodes
Solution Approach 2:
The single current reference source performs the universal function of providing reference current to all pixel cells simultaneously. This multi-functional component replaces multiple individual current sources, ensuring consistent current distribution across the entire sensor array while enabling real-time depth measurement for all pixels
Data Source
AI summary
A programmable current source for use with a time of flight pixel cell includes a first transistor. A current through the first transistor is responsive to a gate-source voltage of the first transistor. A current control circuit is coupled to the first transistor and coupled to a reference current source to selectively couple a reference current of the reference current source through the first transistor during a sample operation. A sample and hold circuit is coupled to the first transistor to sample a gate-source voltage of the first transistor during the sample operation. The sample and hold circuit is coupled to hold the gate-source voltage during a hold operation after the sample operation substantially equal to the gate-source voltage during the sample operation. A hold current through the first transistor during the hold operation is substantially equal to the reference current.