SPAD Detection Circuit with Adjustable Threshold for Pulse Width Control
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Solution Overview
Problem
Current single-photon avalanche diode (SPAD) units in laser radar systems face issues with pulse width constancy, leading to saturation under strong ambient light, reduced signal-to-noise ratio, and loss of valid information due to unadjustable pulse widths and dead time in both passive- and active-quenching types.
Innovation Solution
A detection circuit that includes a single-photon avalanche diode and a comparator with an adjustable threshold, allowing the pulse width to be adjusted based on incident light intensity, enabling dynamic range expansion and improved signal processing by matching the output pulse width with the transmission pulse width of the laser radar.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a passive-quenching SPAD unit is used with a constant flipping threshold buffer, then the circuit structure is simple, but the output pulse width is constant and cannot be adjusted to match transmission pulse width, leading to reduced signal-to-noise ratio and ranging performance
Solution Approach 1:
The patent transforms the constant threshold buffer into a dynamic threshold circuit that can adjust its flipping threshold based on feedback signals. This allows the output pulse width to be variable and match the transmission pulse width, thereby optimizing the signal-to-noise ratio and ranging performance while maintaining reasonable circuit complexity through controlled dynamics.
Solution Approach 2:
The patent changes the parameter of the flipping threshold from constant to adjustable. By modifying the threshold parameter dynamically, the circuit can adapt the output pulse width to match the transmission pulse width, improving signal processing performance without significantly increasing overall circuit complexity.
2Device complexity
If a passive-quenching SPAD unit is used, then the circuit structure is simpler, but the device saturates under strong ambient light causing failure of distance measurement
Solution Approach 1:
The patent introduces a feedback mechanism where the output signal is fed back to control the threshold of the buffer circuit. This feedback loop allows the system to automatically adjust its sensitivity in response to ambient light conditions, preventing saturation under strong ambient light while maintaining simple circuit architecture through feedback-based control.
3Adaptability or versatility
If an active-quenching SPAD unit is used, then the pulse width can be expanded with photon sequence, but the circuit has a dead time during which the NMOS transistor is continuously conductive, causing signal distortion and loss of valid information
Solution Approach 1:
The patent extracts the dead time problem from the active-quenching mechanism by using a passive-quenching approach with adjustable threshold. This removes the continuous conduction state that causes dead time, allowing the circuit to maintain adaptability in pulse width expansion while eliminating information loss during what would otherwise be dead time periods.
4Ease of operation
If the output pulse width is kept constant in passive-quenching SPAD, then the circuit is easier to implement, but the pulse width cannot be adjusted adaptively to transmission pulse width, causing optimized signal-to-noise ratio to be unobtainable
Solution Approach 1:
The patent introduces dynamic adjustability to the threshold circuit while maintaining ease of implementation. The dynamic threshold mechanism allows the pulse width to be adapted to match the transmission pulse width, optimizing signal-to-noise ratio without requiring complex external control systems, thus balancing ease of operation with measurement precision.
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 enhances the dynamic range of the SPAD device, reduces saturation, and optimizes the signal-to-noise ratio by allowing pulse width adjustment, enabling accurate distance measurement and reflectivity determination even under strong ambient light conditions.
Implementation Method 1
a single-photon avalanche diode, configured to generate a photocurrent in response to an incident photon
Implementation Method 2
a comparator, having a first input terminal to be inputted with a signal indicating an adjustable threshold, and a second input terminal coupled to the single-photon avalanche diode to be inputted with an electrical signal representing the photocurrent; the comparator is configured to output a waveform based on a comparison result between the electrical signal and the signal indicating the adjustable threshold
Data Source
AI summary
A detection circuit for adjusting a width of output pulses is provided, including: a single-photon avalanche diode configured to generate a photocurrent according to an incident photon; and a comparator, having a first input terminal to receive a signal indicating an adjustable threshold, and a second input terminal coupled to the single-photon avalanche diode to receive an electrical signal representing the photocurrent. The comparator outputs a waveform based on a comparison result between the electrical signal and the signal indicating the adjustable threshold. When a plurality of photons are received by the single-photon avalanche diode within a short time period, a pulse width of an output signal of the circuit is increased. A number of photons can be obtained according to the pulse width of the signal, and a dynamic range of the single-photon avalanche diode device is improved. A pulse width of a single-photon signal can be adjusted.