Depth Pixel Switching Circuit for Polarization Stability
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Solution Overview
Problem
Existing image acquisition systems using non-pinched photodiodes, particularly those based on III-V materials like InGaAs, face challenges in maintaining polarization for high performance and signal-to-noise ratio, especially at high operating frequencies, and require complex readout circuits that compromise between consumption and detection accuracy.
Innovation Solution
A reading circuit for depth image acquisition devices employs a switching circuit with multiple storage elements and amplification stages, allowing capacity reversal and exchange between amplification branches to improve signal-to-noise ratio and simplify digital processing, suitable for non-pinched photodiodes including InGaAs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If non-pinched photodiodes are used for depth detection, then the device can operate at high frequencies and is suitable for III-V materials like InGaAs, but maintaining polarization becomes difficult and signal-to-noise ratio deteriorates
Solution Approach 1:
An intermediate capacitor is introduced between the photodiode and the readout circuit. This capacitor acts as a mediator that stores the photo-generated charges and maintains the polarization state of the photodiode, allowing the system to operate at high frequencies without compromising polarization stability. The capacitor decouples the high-speed operation from the polarization maintenance requirement.
2Adaptability or versatility
If non-pinched photodiodes are used, then III-V materials like InGaAs can be utilized for infrared detection, but detection accuracy and signal-to-noise ratio are compromised
Solution Approach 1:
The capacitor serves as an intermediary that enables the use of non-pinched photodiodes made from III-V materials while maintaining detection accuracy. By storing charges and maintaining polarization, the capacitor compensates for the lack of inherent polarization maintenance in non-pinched structures, allowing InGaAs and similar materials to achieve high detection accuracy in the infrared range.
Solution Approach 2:
The capacitor performs preliminary charge storage and polarization maintenance before the readout operation. This preliminary action ensures that when the readout occurs, the photodiode is already in the correct polarized state, enabling accurate detection even with non-pinched structures that cannot maintain polarization inherently.
3Measurement precision
If complex readout circuits are used to maintain polarization in non-pinched photodiodes, then detection accuracy can be maintained, but device complexity increases and consumes more power
Solution Approach 1:
The polarization maintenance function is extracted from the complex readout circuit and assigned to a simple capacitor. This extraction simplifies the readout circuit by removing the need for complex active polarization control mechanisms, while the capacitor handles the polarization maintenance passively, reducing both complexity and power consumption.
Solution Approach 2:
The capacitor provides self-service by automatically maintaining photodiode polarization through passive charge storage. This eliminates the need for active control circuits that would increase complexity and power consumption, as the capacitor naturally maintains the electrical state required for accurate detection without external intervention.
4Measurement precision
If integration over a large number of periods is performed to improve phase shift estimation, then measurement precision improves, but acquisition time increases
Solution Approach 1:
The capacitor performs preliminary charge accumulation during the integration period, storing photo-generated charges in advance. This preliminary action allows for faster readout and reduces the total acquisition time, as the charges are already prepared and stored, enabling quicker measurement cycles while maintaining the benefits of integrated signal accumulation.
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 signal-to-noise ratio and simplifies digital processing, maintaining polarization and improving detection accuracy while operating at high frequencies, making it suitable for non-pinched photodiodes like InGaAs.
Implementation Method 1
each depth pixel of the set comprising a reading circuit associated with a photo-detector
Implementation Method 2
a storage element comprising an integration capacity configured to acquire charge samples from the photo-detector during sampling phases
Data Source
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AI summary
An image acquisition device having a set of depth pixels, each depth pixel comprising a reading circuit associated with a photodetector (PD), the reading circuit being provided with a switching circuit (120) configured to: - adopt a first configuration so as to couple a first electrode (101a) of an integration capacitor (Ca) to a first reading node (NL1) and a second electrode (102a) of the integration capacitor (Ca) to a detection node (ND), then, - adopt a second configuration so as to couple the first electrode (101a) of the integration capacitor (Ca) to the detection node (ND) and the second electrode (102a) of the integration capacitor (CINT1) to the reading node (NL).