SPAD Array Pixel-Level Bias Control for Sensitivity Uniformity
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Solution Overview
Problem
Single-photon avalanche diode (SPAD) arrays face variations in sensitivity and noise due to differences in breakdown voltage among elements, leading to inconsistent performance across the array.
Innovation Solution
A bias control circuit sets different bias voltages for each sensing element in the array, allowing for equalized sensitivity and noise reduction by applying a global bias voltage and an excess bias, enabling dynamic adjustment of sensitivity across the array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a global bias voltage is applied to all sensing elements, then the device complexity is reduced, but the sensitivity uniformity across the array deteriorates
Solution Approach 1:
The bias control system is segmented into a global bias generator that provides a common baseline voltage to all sensing elements, and local bias circuits in each sensing element that add element-specific excess bias voltages. This segmentation allows the majority of the bias control to be centralized (reducing overall complexity) while permitting local adjustments to compensate for element-to-element variations in breakdown voltage, thereby achieving uniform sensitivity across the array.
2Measurement precision
If the bias voltage is increased to improve photon detection sensitivity, then the sensitivity increases, but the noise level increases
Solution Approach 1:
The invention changes the bias voltage parameter dynamically and individually for each sensing element. By measuring the breakdown voltage of each element and setting its operating bias voltage to a fixed margin above its specific breakdown voltage, the system optimizes the balance between sensitivity and noise for each element. This parameter adjustment ensures that elements with lower breakdown voltages receive less excess bias (reducing their noise) while elements with higher breakdown voltages receive more excess bias (maintaining their sensitivity), thereby achieving uniform sensitivity across the array with optimized noise performance.
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 uniformity of photon detection sensitivity and reduces noise levels, allowing for tailored sensitivity regions within the array to optimize detection capabilities.
Implementation Method 1
In a SPAD, a p-n junction is reverse-biased at a level well above the breakdown voltage of the junction. At this bias, the electric field is so high that a single charge carrier injected into the depletion layer, due to an incident photon, can trigger a self-sustaining avalanche.
Implementation Method 2
a single charge carrier injected into the depletion layer, due to an incident photon, can trigger a self-sustaining avalanche
Data Source
AI summary
A sensing device includes an array of sensing elements. Each sensing element includes a photodiode, including a p-n junction, and a local biasing circuit, coupled to reverse-bias the p-n junction at a bias voltage greater than a breakdown voltage of the p-n junction by a margin sufficient so that a single photon incident on the p-n junction triggers an avalanche pulse output from the sensing element. A bias control circuit is coupled to set the bias voltage in different ones of the sensing elements to different, respective values that are greater than the breakdown voltage.