SPAD Gating Filter Circuit for Spurious Transient Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Single-photon detectors, particularly InGaAs/InP SPADs, face challenges in reducing dark counts and afterpulses due to spurious transients caused by gating signals, which obscure photon absorption signals and affect detection efficiency.
Innovation Solution
A photon detection system comprising an avalanche photodiode, a biasing circuit, and a non-reflective filter circuit that applies a periodic gating signal to reverse bias the photodiode and uses low-pass and high-pass filters to separate and attenuate spurious transients from photon-induced signals, improving signal-to-noise ratio and detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a periodic gating signal is applied to the SPAD to arm and quench the device, then the signal-to-noise ratio is improved, but spurious transients are generated that obscure photon detection signals
Solution Approach 1:
The patent applies a periodic gating signal to the SPAD that intentionally generates spurious transients at known frequencies. These harmful transients are then converted into beneficial information by using a notch filter to remove them, leaving the genuine photon detection signals intact. The gating signal's harmful effect is transformed into a useful filtering criterion.
Solution Approach 2:
The patent introduces a notch filter as an intermediary component between the SPAD output and the detection system. This filter mediates by selectively removing spurious transients at the gating frequency while allowing genuine photon signals to pass through, thus resolving the contradiction between noise reduction and signal preservation.
2Speed
If the gate frequency is increased to improve detection speed, then high-speed detection is achieved, but spurious transients become more prominent and harder to distinguish from genuine signals
Solution Approach 1:
The patent replaces mechanical or temporal discrimination methods with an electrical filtering approach. Instead of relying on time-based separation between gating transients and photon signals, the system uses a notch filter to electronically remove spurious frequencies, enabling high-speed detection without sacrificing accuracy.
Solution Approach 2:
The patent changes the frequency parameter of the gating signal to operate at high speeds while simultaneously using a notch filter tuned to that frequency to remove the resulting spurious transients. This parameter adjustment, combined with frequency-selective filtering, resolves the contradiction between speed and accuracy.
3Object-affected harmful factors
If a low-pass filter is applied to reduce noise, then noise attenuation is achieved, but the gate frequency components may be attenuated along with the noise
Solution Approach 1:
The patent segments the frequency spectrum into distinct components: low-frequency noise, mid-frequency gating signals, and high-frequency photon detection signals. By using a notch filter targeted at the specific gating frequency rather than a broad low-pass filter, the system selectively removes noise at the gating frequency without attenuating the gate signal itself or genuine photon signals.
Solution Approach 2:
The notch filter serves as an intermediary that selectively interacts with only the spurious gate frequency components, leaving other frequency components including the gate signal and photon detection signals unaffected. This selective mediation preserves gate signal integrity while achieving noise attenuation.
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 system effectively reduces spurious transient interference, enhancing detection efficiency and stability by filtering out unwanted frequencies while maintaining a high signal-to-noise ratio, even at high gate repetition frequencies, thus improving performance in applications like quantum communication.
Implementation Method 1
The non-reflective filter circuit is configured to receive, at an input port, the photodiode signal from the transmission line, and provide, at a first output port, a first filtered output signal by applying a low-pass filter with a first cut-off frequency to the received photodiode signal
Implementation Method 2
The non-reflective filter circuit may be further configured to provide, at a second output port, a second filtered output signal by applying a high-pass filter with a second cut-off frequency to the received photodiode signal
Implementation Method 3
The input port of the non-reflective filter circuit is configured to be impedance matched to the transmission line up to a frequency higher than a gate frequency of the gating signal
Implementation Method 4
The avalanche photodiode is configured to generate a photodiode signal in response to an incident photon
Implementation Method 5
Single-Photon Avalanche Diodes (SPADs) are a type of single-photon detectors that is commonly employed for high speed single-photon detection in the visible and near-infrared (NIR) optical range
Data Source
Figure 1~4
Figure 5~6
Figure 7
AI summary
A photon detection system comprising an avalanche photodiode configured to generate a photodiode signal in response to an incident photon. The photon detection system also comprises a biasing circuit configured to supply a gating signal to the avalanche photodiode. The gating signal is a periodic signal configured to reverse bias the avalanche photodiode above and below its breakdown voltage for photon detection during each period. The photon detection system further comprises a non-reflective filter circuit configured to receive, at an input port, the photodiode signal, and provide, at a first output port, a first filtered output signal by applying a low-pass filter with a first cut-off frequency to the received photodiode signal.