Photodetector Reset Circuit with Variable Current for Lower Dead Time
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Solution Overview
Problem
Conventional active quenching circuits for avalanche photodiodes (APDs) cause excessive heat and potential destruction due to uncontrolled current flow, leading to slow operation and crosstalk, while passive quenching circuits are inefficient in resetting the APD.
Innovation Solution
A photodetector with a reset circuit and control circuit that uses a variable current source to stepwise or continuously increase current to the cathode of the APD after detection, minimizing parasitic capacitance and reducing dead time by quickly returning the cathode voltage to an initialization state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional active quenching circuit is used to reset the APD at high speed, then the reset speed is improved, but excessive heat is generated and the APD may be destroyed
Solution Approach 1:
The patent employs a variable current source that dynamically adjusts the reset current based on the APD's operating state. The current is not fixed but varies in response to feedback signals from the APD, allowing the system to optimize reset speed while preventing excessive current that would generate harmful heat.
Solution Approach 2:
The patent incorporates a feedback mechanism where the APD's state is monitored and used to control the reset current. The feedback signal from the APD modulates the variable current source, ensuring that the reset current is appropriately adjusted to achieve fast resetting without causing excessive heat generation or damaging the APD.
2Speed
If a conventional active quenching circuit is used, then the reset speed is improved, but crosstalk occurs between adjacent APDs
Solution Approach 1:
The variable current source dynamically adjusts the reset current magnitude based on the APD's state and the detected light intensity. This dynamic adjustment allows the system to use lower current levels when possible, reducing the likelihood of crosstalk to adjacent APDs while still achieving adequate reset speed.
Solution Approach 2:
The patent changes the current parameter adaptively based on operating conditions. By modulating the reset current magnitude according to the APD state and detected signal strength, the system optimizes the balance between reset speed and crosstalk prevention, using minimal necessary current to avoid interfering with neighboring photodetectors.
3Device complexity
If a passive quenching circuit is used, then the circuit configuration is simplified, but the reset operation becomes slow
Solution Approach 1:
The patent combines the simplicity of passive quenching circuits with the speed of active quenching by using a variable current source that can be rapidly adjusted. The current source is controlled by the APD's state feedback, enabling fast reset operation without requiring complex active circuitry, thus achieving both simplicity and speed.
Solution Approach 2:
The patent uses parameter changes in the current source control to achieve fast resetting. By dynamically adjusting the current magnitude based on feedback from the APD state, the system achieves rapid reset operation while maintaining a relatively simple circuit configuration, bridging the gap between passive and active quenching approaches.
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 effectively prevents re-ignition of the APD and reduces dead time, allowing for faster subsequent light detection and integration of multiple photodetectors on a semiconductor substrate.
Implementation Method 1
a photodetection element that convert received light into an electrical signal
Implementation Method 2
an avalanche photodiode (referred to below as APD). In particular, when an APD is operated in a Geiger mode, the APD has an ability to detect weak light of one photon
Data Source
AI summary
Provided is a photodetector including: a photodetection element; a reset circuit that sets one end of the photodetection element to an initialization voltage after the photodetection element detects light, and that includes a variable current source capable of varying a current to be supplied to the one end of the photodetection element; and a control circuit that stepwise or continuously increases a current to be supplied to the one end of the photodetection element by using the variable current source until the one end of the photodetection element is set to the initialization voltage after the photodetection element detects light.