I-TOF Pixel Circuit With Adaptive Sigma-Delta Background Suppression
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Solution Overview
Problem
Indirect time-of-flight (I-TOF) cameras face challenges in suppressing background light, leading to pixel saturation and reduced depth image quality due to the influence of external light sources like sunlight or indoor lighting.
Innovation Solution
A 2-tap pixel circuit with in-pixel sigma delta and adaptive sigma delta controllers, along with a chopping controller, is employed to selectively switch and differentiate charge storage, effectively removing background light components by alternating signal phases and storage operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If background light suppression is enhanced by increasing sensor sensitivity, then depth image quality improves, but pixel saturation from background light increases
Solution Approach 1:
The patent applies periodic modulation to the light source at a specific frequency, causing the subject-reflected light to be modulated at the same frequency. The sensor then detects this modulated signal while filtering out unmodulated background light, achieving background suppression without pixel saturation
Solution Approach 2:
The patent introduces a modulation frequency as an intermediary characteristic that distinguishes the desired signal from background light. By modulating the light source and detecting at the same frequency, the system separates the subject signal from background interference, improving depth image quality without saturation
2Measurement precision
If background light subtraction is performed to remove background influence, then depth measurement accuracy improves, but measurement precision deteriorates due to saturation
Solution Approach 1:
The patent uses periodic modulation of the light source and synchronous detection at the modulation frequency. This allows the sensor to selectively amplify the modulated subject signal while rejecting unmodulated background light, maintaining signal reliability and distance accuracy simultaneously
3Measurement precision
If photodiode light amount is increased to improve signal reception, then depth image quality improves, but background light saturation increases
Solution Approach 1:
The patent modulates the light source periodically and uses synchronous detection to extract only the modulated signal component. This allows the system to increase effective signal reception while the background light, being unmodulated, is automatically rejected and cannot cause saturation
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 solution prevents pixel saturation and enhances depth image quality by accurately subtracting background light, improving signal-to-noise ratio and distance accuracy, thereby securing reliable depth images even in high background light conditions.
Implementation Method 1
a 2-tap pixel circuit including pixel capacitors, storage switches, and transfer switches formed by being branched into two taps from the photodiode
Data Source
AI summary
A pixel circuit for background light suppression includes: a 2-tap pixel circuit including first and second pixel capacitors, first and second storage switches, and first and second transfer switches; an in-pixel sigma delta circuit including a plurality of switching switches and a storage capacitor for storing charge transferred from the first and second pixel capacitors; an adaptive sigma delta controller configured to determine switching states of the plurality of switching switches according to a first state of the first pixel capacitor, or a second state of the second pixel capacitor, or both; and a chopping controller configured to instruct the storage switches and the transfer switches of the 2-tap pixel circuit to be selectively switched according to an output of the adaptive sigma delta controller.