SPAD Excess Bias Voltage Measurement for Temperature-Stable Timing
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Solution Overview
Problem
Single photon avalanche diodes (SPADs) experience systematic timing jitter due to temperature changes, affecting their physical parameters like Dark Count Rate and Photon Detection Probability, as the excess bias voltage varies with temperature, necessitating an adaptive bias voltage adjustment to minimize environmental influences.
Innovation Solution
An electric circuit arrangement that determines the excess bias voltage of a SPAD with high precision and speed, using a controllable switching circuit and evaluation circuit to measure the voltage jump and linear increasing slope of the output signal, allowing for the calculation of the excess bias voltage using a time-to-digital converter or digital counter, without the need for a dedicated reference circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the bias voltage VHV is kept constant, then the circuit operation is simple, but the excess bias voltage Vex changes with temperature causing systematic timing jitter
Solution Approach 1:
The patent implements a feedback mechanism where the excess bias voltage Vex is continuously monitored and measured. The measured value is fed back to control the bias voltage VHV, creating a closed-loop system that automatically compensates for temperature-induced variations, thereby maintaining stable timing performance without manual intervention.
Solution Approach 2:
The patent dynamically adjusts the bias voltage parameter VHV based on measured excess bias voltage Vex to compensate for temperature changes. By changing the operating parameters in response to environmental conditions, the system maintains consistent timing precision across varying temperatures.
2Measurement precision
If the excess bias voltage Vex is measured with high precision, then the timing jitter is reduced, but the measurement time increases
Solution Approach 1:
The patent performs preliminary measurement of the excess bias voltage Vex at the beginning of operation or during initialization. This preliminary action establishes a baseline value that can be used for subsequent timing operations, reducing the need for continuous high-precision measurements and thereby minimizing time loss while maintaining measurement accuracy when needed.
3Measurement precision
If a dedicated reference circuit is used to measure Vex, then the measurement precision is improved, but the device area and power consumption increase
Solution Approach 1:
The patent employs a multi-functional circuit design where the same circuit components serve both as the SPAD detection circuit and as the measurement circuit for excess bias voltage. By making the circuit universal, the patent eliminates the need for separate dedicated reference circuits, thereby reducing device area and power consumption while maintaining measurement precision through clever circuit reuse.
Solution Approach 2:
The patent merges the SPAD operation circuit and the excess bias voltage measurement circuit into a single integrated structure. By combining these functions, the patent reduces the overall device area and power consumption that would result from having separate dedicated circuits, while still achieving high-precision measurement of Vex through the unified circuit design.
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
Enables precise and rapid determination of the excess bias voltage, maintaining SPAD performance across temperature changes with minimal power consumption and area, ensuring consistent physical parameters.
Implementation Method 1
When the SPAD is reverse biased with a bias voltage VHV higher than a breakdown voltage VBD, an electron hole pair is generated, when a photon hits the SPAD. Due to the high electrical field, the SPAD generates a very short high peak current pulse.
Implementation Method 2
The controllable switching circuit is configured to couple the output terminal to the reference terminal in a first operational cycle of the circuit arrangement so that a voltage jump to the level of the excess bias voltage occurs at the output terminal
Implementation Method 3
The controllable switching circuit is further configured to couple the output terminal to the supply terminal in a subsequent second operational cycle. During the charging of the output terminal, the single photon avalanche diode stays quenched
Data Source
AI summary
An electric circuit arrangement to determine a level of an excess bias voltage of a single photon avalanche diode comprises an evaluation circuit being configured to determine a level of an excess bias voltage of the single photon avalanche diode in dependence on a signal course of an output signal of the single photon avalanche diode. In a first operational cycle of the circuit arrangement a voltage jump to the level of the excess bias voltage is generated at an output terminal, when a photon hits a photosensitive area of the single photon avalanche diode. In a subsequent second operational cycle, the output terminal of the single photon avalanche diode is coupled to a supply terminal.