Variable RC Active Quenching Circuit for SPAD
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Solution Overview
Problem
Existing active quenching circuits for single photon avalanche diodes (SPADs) fail to achieve full quenching, leading to prolonged dead times and reduced photodetection rates due to inefficiencies in charge carrier removal from the depletion region.
Innovation Solution
An active quenching circuit with a variable RC constant, comprising n-channel transistors, inverters, and a logic gate, which alternates between low, high, and intermediate RC values during quenching, hold-off, and recharge periods to maintain the SPAD voltage above threshold and facilitate rapid recharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive quenching circuits with large quenching resistors are used to ensure full quenching of charge carriers, then quenching efficiency is improved, but recharge time increases significantly
Solution Approach 1:
The patent applies dynamics by making the quenching resistance variable rather than fixed. The circuit transitions between high resistance state during quenching and low resistance state during recharge, allowing optimal performance in both phases. This is achieved through active circuit elements that dynamically adjust the resistance based on the operational phase.
Solution Approach 2:
The patent implements periodic action through oscillating or switching behavior between quenching and recharge phases. The active quenching circuit periodically transitions between high and low resistance states, creating a rhythmic pattern of quenching followed by rapid recharge, which resolves the contradiction between thorough quenching and fast recovery.
2Productivity
If active quenching circuits are used to reduce dead time, then photodetection rate is improved, but full quenching of charge carriers is not achieved
Solution Approach 1:
The patent uses dynamic resistance adjustment where the quenching resistance is high during the quenching phase to ensure complete carrier removal, then switches to low resistance during recharge to enable fast recovery. This dynamic behavior allows the circuit to achieve both full quenching and short dead time.
Solution Approach 2:
The patent changes the resistance parameter over time and operational phase. By varying the resistance value between high (during quenching) and low (during recharge), the circuit achieves complete quenching when needed while enabling rapid recharge to maintain high photodetection rates.
3Device complexity
If fixed RC constant circuits are used, then circuit simplicity is maintained, but inability to achieve both full quenching and short dead time exists
Solution Approach 1:
The patent introduces dynamic elements that automatically adjust the RC constant based on operational phase. The circuit uses switching mechanisms or oscillating components to vary resistance and/or capacitance values, transforming a static RC circuit into a dynamic one that adapts to different operational requirements.
Solution Approach 2:
The patent creates a multi-functional circuit where the same RC circuit serves dual purposes: achieving full quenching during the quenching phase and enabling rapid recharge during the recovery phase. This is accomplished through time-varying parameters that allow the circuit to perform different functions at different times.
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 circuit achieves full quenching of the SPAD while maintaining a short dead time, enabling high photodetection rates by effectively managing the RC constant to ensure efficient charge removal and rapid recovery.
Implementation Method 1
When a photon-generated carrier (via the internal photoelectric effect) is injected into the depletion region of the PN junction, a self-sustaining avalanche is caused
Implementation Method 2
a photon-generated carrier (via the internal photoelectric effect) is injected into the depletion region
Implementation Method 3
the SPAD is quenched, which is to say that the carriers are flushed from the depletion region
Data Source
AI summary
A single photon avalanche diode (SPAD) has a cathode coupled to a high voltage supply and an anode coupled to a first node. A photodetection circuit includes: a first n-channel transistor having a drain coupled to the first node, a source coupled to ground, and a gate coupled to a third node; a second n-channel transistor having a drain coupled to the first node, a source coupled to ground, and a gate coupled to a second node; and an inverter having an input coupled to the first node and an output coupled to an intermediate node. A current starved inverter has an input coupled to the intermediate node and an output coupled to the second node, a logic gate has inputs coupled to the intermediate node and the second node, and an output coupled to the third node.