SPAD Output Bias Circuit for High-Illumination Saturation Control
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Solution Overview
Problem
SPAD pixels face saturation issues in high illumination environments, leading to reduced photon detection efficiency and power consumption due to frequent avalanches and inadequate recharge times, which complicates the design of compact and low-power detection circuits.
Innovation Solution
A dynamic output bias signal is employed to adjust the output signal circuitry threshold and SPAD bias voltage based on saturation levels, allowing the photon detection circuit to switch between high and low sensitivity modes, and utilizing single gate transistors to manage voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the SPAD operates in high illumination environments, then the photon detection capability is maintained, but the SPAD becomes saturated leading to reduced detection efficiency
Solution Approach 1:
The patent implements dynamic adjustment of the output signal circuitry threshold voltage based on real-time saturation detection. The threshold voltage is continuously adapted to match the operating conditions, transitioning between high sensitivity mode (low threshold) and low sensitivity mode (high threshold) to prevent saturation while maintaining detection efficiency across varying illumination levels
Solution Approach 2:
The patent employs a feedback mechanism where the saturation level of the SPAD is monitored and fed back to dynamically adjust the output signal circuitry threshold. This closed-loop control allows the system to detect when the SPAD is approaching saturation and automatically raise the threshold to prevent further saturation, thereby maintaining reliable photon detection
2Measurement precision
If the SPAD bias voltage is increased to improve sensitivity, then photon detection capability enhances, but power consumption increases
Solution Approach 1:
The patent dynamically adjusts the SPAD bias voltage based on saturation conditions and photon event rate. During high illumination conditions, the bias voltage is reduced to lower power consumption while maintaining adequate detection capability through threshold adjustment. During low illumination, the bias voltage is increased to maximize sensitivity, optimizing the trade-off between power consumption and detection performance
Solution Approach 2:
The patent changes the operating parameters (SPAD bias voltage and output threshold voltage) adaptively based on environmental conditions. By modulating these parameters in response to photon event rate and saturation level, the system achieves high sensitivity when needed while reducing power consumption during high illumination periods
3Adaptability or versatility
If the output signal circuitry threshold is fixed, then the circuit design is simple, but the circuit cannot adapt to high illumination conditions
Solution Approach 1:
The patent implements a dynamic threshold adjustment mechanism that automatically adapts the output signal circuitry threshold based on saturation detection. This allows the circuit to transition between operational modes without manual intervention, providing adaptability to varying illumination conditions while keeping the overall circuit architecture relatively simple through automated control
Solution Approach 2:
The circuit employs self-service control where the saturation detection mechanism automatically triggers threshold adjustment without external control signals. The system monitors its own state and self-regulates the threshold voltage to maintain optimal operation across different illumination levels, reducing the need for complex external control systems
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 photon detection performance in high illumination conditions by maintaining sensitivity and reducing power consumption while adhering to area and power requirements, preventing circuit paralysis and improving detection accuracy.
Implementation Method 1
A SPAD is a solid state photodetector that uses a p-n junction to form a diode to enable the flow of current in an instance in which a particle of electromagnetic energy, such as a photon, encounters the p-n junction
Implementation Method 2
A SPAD pixel is configured to output a voltage pulse in an instance in which one or more photons encounter the SPAD of the SPAD pixel
Data Source
AI summary
An example photon detection circuit, a SPAD sensing device, and a direct time-of-flight detection system comprising a SPAD sensing device configured to operate in a high illumination environments, are provided. The example photon detection circuit includes SPAD circuitry configured to generate a photon detection signal based on a SPAD bias voltage and the number of photons encountering the SPAD. The photon detection circuitry further includes output bias circuitry configured to generate a dynamic output bias signal, wherein the dynamic output bias signal is updated based on the number of photons encountering the SPAD. The example photon detection circuitry further includes output signal circuitry configured to generate a photon detection output signal in an instance in which the photon detection signal exceeds an output signal circuitry threshold, wherein the output signal circuitry threshold is based on the dynamic output bias signal.