Active Quenching Circuit for SPAD Using One-Shot Control
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Solution Overview
Problem
Conventional quenching circuits for Single-Photon Avalanche Diodes (SPADs) face limitations in achieving rapid reset rates and consistent dead-time periods, particularly for single-ended SPADs used in LIDAR systems, leading to issues with after-pulse events and reduced sensitivity to red and NIR wavelengths.
Innovation Solution
An active quenching-recovery circuit utilizing a quenching transistor and a one-shot quench control circuit that actively quenches the SPAD during a delay period following photon detection and then resets it, ensuring a well-controlled dead-time period and preventing after-pulse events, while being compatible with single-ended SPADs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional quenching circuits are used for SPADs, then the circuit structure is simple, but the reset rate is slow and dead-time period is inconsistent
Solution Approach 1:
The patent implements dynamic control of the quenching transistor through a one-shot circuit that automatically adjusts the quenching duration based on the avalanche detection event. This dynamic approach enables rapid reset rates while maintaining circuit simplicity through automated timing control rather than complex manual timing circuits.
Solution Approach 2:
The quenching circuit incorporates feedback mechanisms where the avalanche detection signal triggers the one-shot circuit, which in turn controls the quenching transistor. This feedback loop ensures consistent dead-time periods by automatically adjusting the quenching duration based on actual avalanche events, resolving the contradiction between speed and consistency.
2Reliability
If the dead-time period is extended to prevent after-pulse events, then false detection signals are reduced, but the time resolution is degraded
Solution Approach 1:
The patent optimizes the dead-time period parameter through the one-shot circuit to achieve the minimum necessary duration for preventing after-pulse events. By precisely controlling this parameter rather than using fixed extended periods, the circuit maintains high detection accuracy while minimizing time loss and preserving time resolution for LIDAR applications.
3Speed
If active quenching is implemented for rapid reset, then the reset speed is improved, but the circuit complexity increases
Solution Approach 1:
The patent introduces a one-shot circuit as an intermediary component that mediates between the avalanche detection signal and the quenching transistor control. This intermediary enables active quenching for rapid reset while keeping the overall circuit complexity manageable by using a standardized timing circuit rather than complex custom control logic.
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 enables faster and more reliable reset of SPADs, improving time resolution and preventing false detection signals, thus enhancing the accuracy and safety of LIDAR systems by providing consistent and rapid reset functionality.
Implementation Method 1
When an incident photon with sufficient energy to liberate an electron enters a SPAD while the SPAD is in this reverse-biased state, the released photo-generated electron are accelerated by the high energy field in the depletion region of the p-n junction, thereby causing an avalanche breakdown (avalanche multiplication of electrons) event
Implementation Method 2
the quench control circuit turns off (de-actuates) the quenching transistor to isolate the SPAD's cathode from the bias voltage source to facilitate the quenching process
Implementation Method 3
the quench control circuit generates a shaped digital pulse that, by way of controlling the quenching transistor, functions to convert the voltage pulse generated by the SPAD into a digital (rectangle shaped) signal suitable for detection by downstream digital sensor circuitry
Data Source
AI summary
A sensor circuit having a Single Photon Avalanche Diode (SPAD) and an active quenching circuit including a quenching transistor controlled by a one-shot (or similar) circuit is disclosed. The quenching transistor applies a reverse-bias voltage level on the cathode of the SPAD. During photon detection events, pulses generated by the SPAD's avalanche breakdown trigger the one-shot circuit to de-actuate the quenching transistor, allowing the cathode potential to drop below the SPAD's breakdown voltage. After a delay period, which is defined by the one-shot's configuration, allows reliable completion of the avalanche breakdown process, the one-shot circuit re-actuates the quenching transistor such that the SPAD's cathode is refreshed to the reverse-bias voltage level. The one-shot circuit is optionally coupled by way of capacitors to the SPAD and the quenching transistor to facilitate implementation using standard CMOS elements. The sensor is suitable for use in a LIDAR system.