3D Imaging Sensor TDC Architecture for Photon Detection
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Solution Overview
Problem
3D imaging systems, particularly LIDARs, face challenges in detecting short inter-arrival time photons under strong background illumination and fast-changing environments, leading to signal saturation and noise accumulation, which degrades image resolution and signal-to-noise ratio (SNR).
Innovation Solution
A time-to-digital converter (TDC) architecture that continuously extracts the arrival time of multiple events within a single laser cycle without stopping conversion, using a time window to improve detection of closely timed photons, allowing for better sharing of TDC resources among pixels and increased conversion rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels in a LIDAR is increased to improve image resolution, then measurement precision is improved, but device complexity and power consumption increase linearly
Solution Approach 1:
Multiple detector elements share a single time-to-digital converter (TDC) resource. The TDC is time-multiplexed across multiple detector elements, allowing one TDC to service many detectors sequentially within each laser cycle, thereby reducing the total number of TDCs needed and lowering device complexity while maintaining high pixel counts for image resolution
Solution Approach 2:
A single TDC performs the time measurement function for multiple detector elements universally. The TDC is designed to accept input from any of the N detector elements and perform the same time-to-digital conversion function for each, making it a multi-functional resource that serves the entire detector array rather than requiring dedicated TDCs for each pixel
2Device complexity
If a single TDC is shared among multiple detector elements to reduce device complexity, then device complexity is reduced, but the maximum activity rate per pixel and signal-to-noise ratio degrade
Solution Approach 1:
The system performs preliminary time-stamping of detected photons by the TDC within each laser cycle. By pre-processing and time-stamping all detected events before the next laser pulse, the system prepares the data in advance, allowing for accurate later analysis and maintaining signal-to-noise ratio even with shared TDC resources
Solution Approach 2:
The TDC operates continuously throughout the entire laser cycle, constantly ready to time-stamp photons as they are detected by any detector element. This continuous operation ensures no detection events are missed and maintains high maximum activity rates, unlike systems that stop the TDC after the first detection
3Device complexity
If the TDC stops conversion after the first photon detection to simplify the architecture, then device complexity is reduced, but photons arriving later in the measurement cycle are missed causing signal loss
Solution Approach 1:
The TDC maintains continuous time-to-digital conversion operation throughout the entire laser cycle without stopping after the first detection. This continuous operation ensures that all photons arriving at any time during the measurement cycle are captured and time-stamped, preventing information loss while maintaining architectural simplicity through a single shared TDC
4Ease of operation
If synchronous TDC conversion is used with START signal at laser pulse emission to simplify timing, then ease of operation is improved, but the first detecting pixel monopolizes the TDC causing pile-up effect and noise accumulation
Solution Approach 1:
The system performs preliminary time-stamping of all detected photons by the continuous TDC before the laser cycle ends. By capturing all photon arrival times in advance and storing them with their detector element identifiers, the system prepares the data for later analysis, preventing pile-up effects during the measurement phase while maintaining simple synchronous START signal operation
Solution Approach 2:
The system dynamically associates each detected photon with its specific detector element and time stamp, creating a dynamic data structure that can be flexibly processed later. This dynamic approach allows the system to handle multiple photons from multiple detectors without conflict, as each photon's data is independently tagged and can be sorted and analyzed after the measurement cycle completes
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 enhances the scalability and SNR of 3D imaging systems, enabling operation with a high number of pixels under strong background illumination and fast-changing conditions, effectively reducing signal saturation and noise accumulation.
Implementation Method 1
a detector comprising a plurality of detector elements for detecting incident photons
Data Source
AI summary
A method of determining 3D information of a target includes emitting a light pulse and detecting a first incident photon by a detector element. The time of incidence of the detection of the first incident photon is determined and at the incidence time, a time window is opened with a predetermined duration. All the photons detected in the window are associated with the time of incidence detection of the first incident photon. The cycle is repeated and further first incident photons open another time window so that to each of the individual detector elements that detect further incident photons in the time windows, other incidence times are associated. The time difference between the received photons and the emitted pulse is determined and new cycles of detecting first incident photons and the opening of a new time window are repeated and 3D information of the target is provided.