Negative Voltage Monitoring Circuit for Accurate SPAD Bias Sensing
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Solution Overview
Problem
Existing negative voltage monitoring systems for SPADs in ToF sensors face accuracy issues due to variations in voltage values and resistance, leading to increased costs when high-precision resistors are used to compensate for these variations.
Innovation Solution
A negative voltage monitoring circuit comprising a first voltage-dividing circuit, first and second amplifier circuits, and an error determination circuit, which includes a voltage-division-ratio control circuit to adjust the voltage division ratio and ensure accurate monitoring of negative voltages applied to the SPAD, without the need for high-precision resistors within the chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external resistor with very high precision is mounted to solve voltage division accuracy, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the voltage division function from the external resistor mounting and integrates it into the chip-based monitoring circuit. The first voltage-dividing circuit is implemented within the chip using standard precision resistors, eliminating the need for high-precision external resistors and simplifying the overall system while maintaining monitoring accuracy.
Solution Approach 2:
The patent creates a virtual copy of the voltage division function through the amplifier-based measurement system. Instead of relying on physical precision resistors, the system uses amplifier circuits with controlled gain to replicate the voltage division effect, achieving equivalent functionality with standard components.
2Ease of manufacture
If standard precision resistors are used in voltage division, then ease of manufacture is improved, but measurement precision deteriorates due to resistance variations
Solution Approach 1:
The patent introduces feedback mechanisms through the amplifier circuits to compensate for resistor variations. The second amplifier circuit processes the voltage after division, and the error determination circuit compares results to detect and correct deviations caused by standard precision resistor variations, maintaining measurement accuracy without requiring high-precision components.
Solution Approach 2:
The patent changes the operational parameters of the measurement system by using amplifier-based voltage processing instead of direct voltage division measurement. The system transforms the voltage signal through controlled amplification stages, changing the parameter domain from raw voltage division ratios to amplified voltage levels that can be more accurately measured and compared.
3Measurement precision
If voltage is directly read in the sensor, then measurement precision is improved, but device complexity increases due to withstand voltage requirements
Solution Approach 1:
The patent introduces an intermediary voltage division circuit as a mediator between the high-voltage sensor terminal and the monitoring circuit. The first voltage-dividing circuit safely steps down the high negative voltage to a level that can be handled by standard precision resistors and amplifier circuits, enabling accurate measurement without direct exposure to high voltages.
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 provides high-accuracy monitoring of negative voltages applied to SPADs, ensuring functional safety and reducing costs by eliminating the need for high-precision resistors, while maintaining precise voltage control and error detection.
Implementation Method 1
a first voltage-dividing circuit that divides a power supply voltage and outputs a first voltage
Implementation Method 2
The first amplifier circuit is configured such that the first voltage is inputted to a noninverting input terminal and an output voltage is subjected to negative feedback
Implementation Method 3
In order to generate avalanche amplification with high sensitivity, a SPAD (Single Photon Avalanche Diode) used for a ToF (Time of Flight) sensor requires the application of a large negative voltage
Data Source
AI summary
[Problem] To implement a negative voltage monitoring circuit with high accuracy.[Solution] A negative voltage monitoring circuit includes a first voltage-dividing circuit, a first amplifier circuit, a second amplifier circuit, and an error determination circuit. The first voltage-dividing circuit divides a power supply voltage and outputs a first voltage. The first amplifier circuit is configured such that the first voltage is inputted to a noninverting input terminal and an output voltage is subjected to negative feedback. The second amplifier circuit is configured such that a second voltage is inputted to the noninverting input terminal, the second voltage being obtained by dividing a potential difference between the power supply voltage and a voltage to be monitored, the voltage being applied to an anode of a light receiving element, and an output voltage is subjected to negative feedback. The error determination circuit outputs an error signal on the basis of a difference between the output of the first amplifier circuit and the output of the second amplifier circuit.