@ElektrodaBot I tried to test the SPAD model with components such as capacitors, diodes, resistors, and switches representing incoming photons. The circuit structure I use is a passive quenching circuit, but the problem I encounter when simulating is that if the two photon clock pulses arrive adjacent to each other, the SPAD has not yet recovered after the quenching period, which will lead to signal errors. Do you have any solution for this problem? I intend to use an active quenching circuit structure instead, but does that ensure that the time after quenching is enough for the SPAD to recover?
(...) ent to each other, the SPAD has not yet recovered after the quenching period, which will lead to signal errors. . Do you have any solution for this problem? I intend to use an active quenching circuit structure instead, but does that ensure that the time after quenching is enough for the SPAD to recover?
Your observation about the limitations of a passive quenching circuit is spot on. In a passive quenching circuit, the time it takes for the SPAD (Single-Photon Avalanche Diode) to recover after a detection event can indeed be too long if photon events are frequent. This is due to the RC time constant associated with the quenching resistor and the SPAD's junction capacitance. When photons arrive in quick succession, the SPAD might not have enough time to reset, which can cause pile-up errors or even the failure to detect subsequent photons.
Switching to an active quenching circuit could be a good solution. Active quenching involves using an electronic circuit to quickly stop the avalanche current after a photon is detected. This rapid quenching significantly reduces the dead time of the SPAD, which is the time after a photon detection during which the SPAD is not able to detect another photon.
The active quenching circuit typically includes a fast comparator to detect the start of the avalanche, followed by a quenching transistor that quickly reduces the voltage across the SPAD below its breakdown voltage, thus quenching the avalanche. The circuit may also include a mechanism for resetting the SPAD so it can quickly return to a state ready for detecting the next photon.
However, whether the active quenching circuit will ensure that the time after quenching is enough for the SPAD to recover depends on the specifics of your SPAD characteristics, the quenching circuit design, and the photon event rate. The recovery time can also be affected by factors such as temperature, the SPAD's afterpulsing probability, and the design of the reset mechanism.
To ensure that the active quenching circuit meets your requirements, you may need to:
1. Characterize the SPAD's parameters, including its junction capacitance, breakdown voltage, and afterpulsing characteristics. 2. Design the active quenching circuit with a sufficiently fast comparator and quenching transistor to quickly stop the avalanche current. 3. Test the active quenching circuit with varying photon detection rates to ensure it can handle the event rate you expect in your application. 4. Implement any additional features to minimize afterpulsing or other effects that could affect the recovery time.
Would you be able to provide more information about the parameters of your SPAD and the expected photon event rate? With more details, I can help you analyze whether an active quenching circuit would be suitable for your application and what specific design considerations you should take into account.
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