SPAD Receiver Single-Channel TDC Noise Reduction
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Solution Overview
Problem
SPAD technology faces challenges in effectively detecting object positions over longer ranges and in high noise environments, such as sunlight interference, which limits its accuracy and applicability in various applications like autonomous driving and fluorescence microscopy.
Innovation Solution
Implementing a SPAD receiver system with a single-channel TDC for multiple photon detections, using asynchronous operation and a pre-defined OFF period to avoid noise-induced detections, and incorporating a SPAD gating circuit, TDC array, and digital signal processor for enhanced time-of-flight measurements and signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If SPAD is used for long-range detection in high noise environments, then detection range is extended, but noise-induced detections block the signal
Solution Approach 1:
The patent implements periodic gating of the SPAD detector, alternately switching between ON and OFF states. During the ON period, photons are detected; during the OFF period, the detector is quenched to avoid noise-induced detections. This periodic action allows the system to extend detection range while blocking noise interference by selectively enabling detection only during appropriate time windows.
Solution Approach 2:
The patent applies preliminary quenching action by setting the OFF period to be longer than the after-pulse period associated with photon detection. This preliminary suppression of the detector state before potential noise events prevents noise-induced detections from occurring, thereby blocking harmful noise factors before they can interfere with the signal.
2Device complexity
If a single-channel TDC is used for multiple photon detections, then device complexity is reduced, but detection accuracy may be compromised
Solution Approach 1:
The patent merges multiple detection functions into a single-channel TDC by sequentially processing photons from different spatial locations and time periods through one conversion channel. The single TDC handles multiple photon detections by resetting and reusing the same hardware resource, thereby reducing device complexity while maintaining measurement precision through proper timing management and asynchronous operation.
Solution Approach 2:
The patent implements dynamic operation of the single-channel TDC, allowing it to adaptively reset and process photons asynchronously as they arrive. The TDC dynamically adjusts its operation between measuring different photons from different SPAD pixels, enabling one hardware channel to serve multiple detection functions without compromising the precision of individual time-of-flight measurements.
3Reliability
If the OFF period is extended to avoid after-pulse noise, then noise-induced detections are reduced, but detection efficiency decreases
Solution Approach 1:
The patent optimizes the OFF period parameter by setting it to be longer than the after-pulse period but not excessively long. This parameter adjustment strikes a balance between two competing requirements: extending the OFF period sufficiently to avoid noise-induced detections (improving reliability) while keeping it short enough to maintain high detection efficiency (preserving productivity). The specific parameter value is tuned to match the characteristics of the SPAD device and operating conditions.
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
This approach enables accurate and efficient detection of object positions over longer ranges with improved signal-to-noise ratio, even in high noise environments, by quenching and recharging the SPAD circuitry to minimize noise interference and enhance photon detection sensitivity.
Implementation Method 1
single-photon avalanche photodiode (SPAD) technology as used for light detection and ranging (Lidar)
Data Source
AI summary
Example aspects are directed to operating a SPAD receiver such as may be used in a light detection and ranging (Lidar) system. In one example, the SPAD receiver has SPAD circuitry for multiple photon detections using a single-channel TDC (time-to-digital converter), and such photon detection is quenched after detection so as to establish an effective pre-defined OFF period. In response, the SPAD circuitry is recharged for a subsequent ON period during which the SPAD circuitry is unquenched (or armed) for further photon detection and processing.