SPAD Control Circuit With Dual-Voltage Sensitivity Protection
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Solution Overview
Problem
The sensitivity characteristic of single photon avalanche diode (SPAD) elements used in distance measurement systems is difficult to improve due to limitations in applying higher voltages without exceeding the withstand voltages of the transistors in the application circuit.
Innovation Solution
A control circuit is designed with a first and second power supply voltage system, where the first power supply voltage is higher than the withstand voltages of the transistors, and a current supply unit, withstand voltage units, and transistors are configured to manage voltage levels and transistor operation to prevent damage, allowing the application of higher voltages to the SPAD element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a higher voltage is applied to the SPAD element to improve sensitivity characteristic, then the sensitivity characteristic is improved, but the transistors in the application circuit may be damaged due to exceeding their withstand voltages
Solution Approach 1:
The power supply system is segmented into two distinct voltage levels: a first power supply voltage (Vdd1) higher than the withstand voltages of transistors applied to the SPAD element, and a second power supply voltage (Vdd2) lower than the withstand voltages applied to the control circuit. This segmentation allows the SPAD element to operate at high voltage for improved sensitivity while the control circuit operates at safe low voltage levels.
Solution Approach 2:
The patent introduces intermediary components including a first withstand voltage unit (40) that holds the lower voltage side of the current supply unit at a voltage equal to or above the second power supply voltage, and a second withstand voltage unit (50) that holds the inverter at a voltage equal to or below the second power supply voltage. These intermediary voltage control units act as mediators between the high voltage SPAD element and the low voltage control circuit, preventing direct voltage conflict and protecting transistors from damage.
2Reliability
If a higher voltage is applied to the SPAD element, then the sensitivity characteristic is improved, but the device complexity increases due to the need for multiple power supply voltage systems and voltage control units
Solution Approach 1:
The first power supply voltage Vdd1 serves multiple functions: it provides the high voltage necessary for SPAD element operation to achieve improved sensitivity, and it is also used by the current supply unit to source current to the SPAD element. The second power supply voltage Vdd2 similarly serves multiple functions by powering the control circuit and providing reference voltages for the withstand voltage units. This multi-functionality reduces the need for additional dedicated components.
Solution Approach 2:
The patent changes the voltage parameter of the power supply system from a single voltage level to a dual voltage level system. By adjusting and controlling different voltage parameters (Vdd1 for SPAD, Vdd2 for control circuit), the system achieves both high sensitivity and transistor protection. The withstand voltage units dynamically adjust voltage levels based on operational requirements, enabling flexible parameter control.
Data Source
AI summary
Provided is a control circuit and a distance measurement system. The control circuit includes first wiring to which a first power supply voltage is applied, second wiring to which a second power supply voltage is applied. The control circuit further includes a current supply unit, a first withstand voltage unit, an inverter connected to a cathode of the SPAD element, and a second withstand voltage unit. Furthermore, the control circuit includes an N-type first transistor that is provided between the cathode of the SPAD element and an input terminal of the inverter, and has a gate connected to the second wiring, and a P-type second transistor that is provided between the second wiring and a source of the first transistor, and has a gate connected to an output terminal of the inverter.