Capacitor-Gated SPAD for Neural Activity Detection
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Solution Overview
Problem
Conventional SPAD architectures in photodetectors for neural activity detection suffer from noise introduction, high power consumption, supply voltage ripple, and increased dead time due to active voltage source gating, which affects the accuracy and efficiency of neural activity measurement.
Innovation Solution
The use of a capacitor to pre-charge and gate the SPAD, allowing for instantaneous arming and reduced power consumption, thereby minimizing noise and supply voltage ripple, and improving the signal-to-noise ratio and spatial and temporal resolution.
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 to detect photons, but noise is introduced into the photodetector output and power consumption increases
Solution Approach 1:
The patent extracts the harmful active voltage source from the gating mechanism and replaces it with a passive capacitor-based approach. The capacitor stores voltage and applies it to the SPAD without requiring continuous active voltage source operation, thereby eliminating the noise and power consumption issues while maintaining detection capability
Solution Approach 2:
The patent introduces a capacitor as an intermediary element between the voltage source and the SPAD. The capacitor acts as a buffer that delivers the necessary bias voltage to the SPAD during the integration period without requiring an active voltage source during operation, thus reducing noise and power consumption while maintaining reliable photon detection
2Reliability
If an active voltage source is used to gate the SPAD, then the SPAD can be selectively biased, but supply voltage ripple is introduced within neighboring SPAD architectures
Solution Approach 1:
The patent removes the active voltage source that generates supply voltage ripple and replaces it with a passive capacitor-based gating mechanism. The capacitor delivers the necessary bias voltage without creating ripple effects that would interfere with neighboring SPAD architectures
Solution Approach 2:
The capacitor serves as an intermediary that isolates the SPAD from voltage ripple effects. By storing the bias voltage and delivering it passively, the capacitor prevents supply voltage ripple from propagating through the circuit and affecting neighboring photodetectors
3Reliability
If conventional gating is used with active voltage source, then the SPAD can be armed and disarmed, but dead time increases affecting measurement efficiency
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor before the integration period begins. This allows the capacitor to be ready to immediately apply the bias voltage to the SPAD when needed, eliminating the delay associated with active voltage source response time and reducing dead time between measurements
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 real-time, high-resolution neural activity detection with reduced noise and power consumption, enhancing the comfort and effectiveness of non-invasive wearable brain interface systems.
Implementation Method 1
A capacitor is configured to be charged, while the SPAD is in a disarmed state, with a bias voltage having a magnitude that is equal to or less than a breakdown voltage of the SPAD
Implementation Method 2
When photons are absorbed by a SPAD, their energy frees bound charge carriers (electrons and holes) that then become free-carrier pairs. In the presence of an electric field created by a reverse bias voltage applied to the diode, these free-carriers are accelerated through a region of the SPAD referred to as the multiplication region. 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
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AI summary
An exemplary non-invasive wearable brain interface system includes a headgear configured to be worn on a head of the user and a plurality of self-contained photodetector units configured to removably attach to the headgear. The photodetector units each include a plurality of photodetectors configured to detect photons of light after the photons reflect from a target within a brain of the user. The brain interface system further includes a master control unit communicatively coupled to each of the photodetector units by way of a plurality of wires and configured to control the photodetector units, the master control unit comprising an input power port configured to connect to a power cable that provides power from a power source for the master control unit and the photodetector units.