SPAD Gating with Pre-charged Capacitor for Neural Detection
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Solution Overview
Problem
Conventional semiconductor-based single-photon avalanche diode (SPAD) architectures for detecting neural activity in the brain face issues with noise introduction, high power consumption, supply voltage ripple, and increased dead time due to the use of active voltage sources for gating.
Innovation Solution
The proposed solution involves gating the SPAD with a pre-charged capacitor instead of an active voltage source, allowing for instantaneous arming, reduced power consumption, and isolation from supply voltage ripple, thereby minimizing noise and improving detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an active voltage source is used to gate the SPAD, then the SPAD can be selectively biased, but noise is introduced into the photodetector output
Solution Approach 1:
The patent extracts the harmful active voltage source from the gating circuit and replaces it with a passive capacitor-based gating mechanism. The capacitor is pre-charged to the breakdown voltage and then disconnected, allowing the SPAD to be gated without introducing noise from active voltage sources during operation.
Solution Approach 2:
The patent applies preliminary action by pre-charging the capacitor to the required breakdown voltage before the gating operation. This pre-preparation allows the capacitor to immediately provide the necessary bias voltage when connected to the SPAD, eliminating the need for active voltage sources during the actual gating process.
2Ease of operation
If an active voltage source is used to gate the SPAD, then the SPAD can be controlled, but power consumption increases
Solution Approach 1:
The patent removes the active voltage source from the gating circuit, thereby eliminating its continuous power consumption. The passive capacitor-based gating mechanism consumes power only during the brief charging phase, not during the actual gating operation.
Solution Approach 2:
The patent implements periodic action by charging the capacitor only when needed for gating operations, rather than maintaining continuous power supply. The capacitor holds the voltage without power consumption during the gating interval, creating a periodic rather than continuous power consumption pattern.
3Reliability
If an active voltage source is used to gate the SPAD, then the SPAD can be biased, but supply voltage ripple is introduced
Solution Approach 1:
The patent extracts the active voltage source that causes supply voltage ripple and replaces it with a passive capacitor. The capacitor provides a stable voltage reference without introducing ripple, as it simply discharges its stored energy rather than actively regulating voltage.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element between the power source and the SPAD gating circuit. This capacitor acts as a voltage buffer that isolates the SPAD from supply voltage variations and ripple, providing a clean voltage reference for gating operations.
4Reliability
If conventional gating methods are used, then the SPAD can be armed, but dead time increases
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor to the breakdown voltage before the gating operation. This preparation allows for instantaneous arming of the SPAD when the capacitor is connected, eliminating the delay associated with voltage source activation in conventional methods.
Solution Approach 2:
The patent replaces the active voltage source control mechanism with a passive capacitor discharge mechanism. This substitution eliminates the need for complex voltage regulation and switching control, enabling faster arming and reducing dead time through simpler, faster capacitor-based gating.
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 enhances the signal-to-noise ratio, increases spatial and temporal resolution, and extends the longevity of the photodetector components by reducing power stress and eliminating supply voltage ripple, making it suitable for real-time neural activity detection.
Implementation Method 1
the capacitor is configured to supply, when the SPAD is put in an armed state, a bias voltage to an output node of the SPAD such that a voltage across the SPAD is greater than a breakdown voltage of the SPAD
Implementation Method 2
a voltage across the SPAD is greater than a breakdown voltage of the SPAD
Implementation Method 3
When photons are absorbed by a SPAD, their energy frees bound charge carriers (electrons and holes) that then become free-carrier pairs
Implementation Method 4
As the free carriers travel through the multiplication region, they collide with other carriers bound in the atomic lattice of the semiconductor, thereby generating more free carriers through a process called impact ionization
Data Source
AI summary
An illustrative wearable brain interface system includes a headgear configured to be worn on a head of a user and a plurality of photodetector units configured to attach to the headgear, the photodetector units each housing a photodetector included in a plurality of photodetectors configured to be controlled by a master control unit to detect photons of light.