SPAD Histogram Memory Segmentation for Lidar Power Reduction
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Solution Overview
Problem
Solid-state Lidar systems face challenges in providing sufficient memory for calculating and storing histograms of time of flight data, leading to increased power consumption and thermal loading, which affects the signal-to-noise ratio and operational range in adverse weather conditions.
Innovation Solution
A circuit and method that reduce the size of RAM/SRAM by using a SPAD control circuit coupled with a timing generator circuit to create a sequence of timing pulses with varying phase offsets, allowing for efficient histogram memory management and improved signal-to-noise ratio by attenuating ambient photons more effectively than signal photons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sufficient memory is provided for calculating and storing histograms of time of flight data, then measurement precision is improved, but use of energy increases and temperature rises
Solution Approach 1:
The patent segments the histogram memory into multiple banks (first bank and second bank) that can be operated independently and concurrently. This allows the system to distribute the memory burden across multiple smaller units, reducing the power consumption and thermal load on any single memory unit while maintaining the total capacity needed for precise histogram calculations.
Solution Approach 2:
The patent implements periodic switching between multiple memory banks using enable signals. The system alternates between writing to one bank and reading from another, or distributes histogram accumulation across multiple banks in a periodic fashion. This periodic operation allows memory banks to be activated only when needed, reducing overall power consumption while maintaining measurement precision.
2Measurement precision
If sufficient memory is provided for calculating and storing histograms of time of flight data, then measurement precision is improved, but temperature increases
Solution Approach 1:
By dividing the histogram memory into multiple segmented banks, the patent reduces the thermal concentration that would occur in a single large memory unit. Each bank generates less heat individually, and the distributed architecture allows better thermal management across the device, maintaining measurement precision without excessive thermal loading.
3Use of energy by moving object
If memory size is reduced, then power consumption decreases, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent uses segmented memory banks that can be selectively activated. By distributing the histogram data across multiple banks and selectively enabling only the necessary banks for current operations, the system reduces power consumption while maintaining sufficient memory capacity to preserve signal-to-noise ratio for the active measurements.
Solution Approach 2:
The multiple memory banks serve universal functions - each bank can store histogram data for different time windows, spatial locations, or measurement conditions. This multi-functionality allows the system to reduce overall power consumption by deactivating unused banks while maintaining the signal-to-noise ratio through appropriate bank selection and configuration.
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 reduces the size and power consumption of the histogram memory, preserving the return impulse shape and enhancing the signal-to-noise ratio, thereby improving the operational range and accuracy of the Lidar system under adverse conditions.
Implementation Method 1
enabling a single-photon-avalanche diode (SPAD) in a pixel of a focal-plane array to detect a photon
Data Source
AI summary
A method includes actuating a laser diode to emit a first series of laser pulses in a first frequency, enabling ap single-photon-avalanche diode (SPAD) in a pixel of a focal-plane array to detect a photon during a first series of enable times defined by a first series of enable pulses in a second frequency greater than the first frequency, and updating a histogram memory based on a photon detected during the first series of enable times.