Histogram Readout Circuit for Photon Time of Flight
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Solution Overview
Problem
Traditional histogram readout methods for determining the time of flight of photons are time-consuming due to the need for streaming large amounts of data and complex calculations, making them unsuitable for fast applications like LiDAR systems.
Innovation Solution
A histogramming readout circuit with a Time to Digital Converter (TDC), memory, and a programmable processor that implements a state machine to efficiently build and analyze histograms, allowing for real-time calculation of the time of flight using weighted averaging and reducing data transfer requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional histogram readout method is used to determine time of flight, then measurement accuracy is maintained, but processing time is excessively long and data transfer requirements are high
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the relationship between histogram peak positions and time of flight values in a lookup table during system initialization. When a measurement is taken, the system simply queries this pre-computed table rather than performing complex Gaussian fitting calculations in real-time, dramatically reducing processing time while maintaining measurement accuracy
Solution Approach 2:
The patent extracts only the essential information needed for time of flight determination by identifying and processing only the peak region of the histogram rather than analyzing the entire histogram dataset. This extraction approach reduces data transfer requirements and processing complexity while preserving measurement accuracy
2Loss of information
If traditional histogram readout method streams all data to computer, then complete data analysis is possible, but data transfer volume and computational complexity increase significantly
Solution Approach 1:
The patent extracts only the peak region data from the complete histogram, identifying the region of interest where the majority of photon arrivals occur. By processing only this extracted subset rather than the entire histogram, the system maintains measurement accuracy while reducing data transfer volume and computational complexity
Solution Approach 2:
The patent creates a simplified copy of the essential measurement information by generating a reduced dataset containing only peak region histogram values and their positions. This copied subset retains the critical information needed for time of flight determination while eliminating redundant data, thereby reducing computational complexity
3Measurement precision
If Gaussian fit calculation is performed to determine peak position, then measurement accuracy is achieved, but processing time and computational resources are excessively consumed
Solution Approach 1:
The patent applies preliminary action by pre-computing the relationship between histogram peak positions and corresponding time of flight values during system initialization and storing these relationships in a lookup table. During actual measurements, the system simply queries this pre-computed table based on the observed peak position, achieving measurement accuracy equivalent to Gaussian fitting but with minimal calculation time
Solution Approach 2:
The patent creates a simplified computational model by copying the essential relationship between peak position and time of flight into a lookup table structure. This copied relationship allows the system to achieve accurate time of flight determination through simple table lookup operations rather than performing complex Gaussian fitting calculations in real-time
Data Source
AI summary
A histogramming readout circuit is described. The readout circuit comprises a time to digital converter (TDC) configured to continually report time-stamps defining an arrival time of a laser clock and a signal output from a photosensor. Memory is provided for 10 storing TDC events. A programmable processor is configured to implement a state machine. The state machine being operable to save a time-stamp when a TDC event is detected; determine the time of flight of each of the photons detected by the photosensor; use each calculated time of flight to address a memory location; build up a histogram of the TDC data values using the memory locations as time-bins; and maintain a pointer to a maximum memory location where the highest number of TDC event resides. A calculator is operable to read the value of the maximum memory location and one or more adjacent time-bins either side for processing.