SPAD Excess Bias Measurement Using Output Voltage Transients
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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 analyze the output signal's voltage jump and linear increasing slope, allowing for the calculation of the excess bias voltage using a time-to-digital converter or digital counter, without requiring 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 used to adjust the bias voltage VHV. The circuit measures the actual Vex value and feeds this information back to the bias voltage generator, which then adapts VHV to compensate for temperature-induced changes, thereby maintaining stable timing performance.
Solution Approach 2:
The patent dynamically changes the bias voltage parameter VHV based on the measured excess bias voltage Vex and temperature conditions. Instead of keeping VHV constant, the system adjusts this parameter in real-time to compensate for environmental variations, transforming a static parameter into a dynamic one that adapts to changing conditions.
2Reliability
If the excess bias voltage Vex is compensated for temperature changes, then timing jitter is reduced, but the device complexity increases due to additional control circuits
Solution Approach 1:
The patent employs a self-service approach where the SPAD device itself provides the information needed for compensation. The excess bias voltage Vex, which is an inherent parameter of the SPAD, is measured directly from the device and used to control the bias voltage adjustment. This eliminates the need for external temperature sensors and complex temperature compensation circuits.
Solution Approach 2:
The patent makes the bias voltage VHV serve multiple functions: it not only operates the SPAD in breakdown mode but also dynamically compensates for temperature effects. The single bias voltage control mechanism handles both the operational biasing and the temperature compensation, reducing the need for separate control circuits.
3Measurement precision
If a dedicated reference circuit is used to determine excess bias voltage, then measurement precision is high, but the area consumption increases
Solution Approach 1:
The patent uses the excess bias voltage Vex itself as an intermediary quantity that carries information about both the SPAD's operational state and the temperature effects. By measuring Vex and using it as the control signal for bias voltage adjustment, the system eliminates the need for separate reference circuits while maintaining measurement precision.
Solution Approach 2:
The patent extracts the essential information needed for temperature compensation directly from the excess bias voltage Vex measurement. Instead of using a complex dedicated reference circuit to determine temperature effects, the system extracts the necessary compensation data from the inherently present Vex parameter, simplifying the overall circuit architecture.
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 area and power consumption, ensuring consistent physical parameters and reducing timing jitter in applications like distance measurement.
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. The evaluation circuit is configured to determine the level of the excess bias voltage in dependence on a signal course of the output signal.
Data Source
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AI summary
An electric circuit arrangement (1a, 1b) to determine a level of an excess bias voltage of a single photon avalanche diode comprises an evaluation circuit (300) being configured to determine a level of an excess bias voltage (Vex) of the single photon avalanche diode (100) in dependence on a signal course of an output signal (Van) of the single photon avalanche diode. In a first operational cycle of the circuit arrangement (1a, 1b) a voltage jump to the level of the excess bias voltage (Vex) is generated at an output terminal (40), when a photon hits a photosensitive area of the single photon avalanche diode (100). In a subsequent second operational cycle, the output terminal (40) of the single photon avalanche diode is coupled to a supply terminal (10).