Pipelined Histogram Pixel With SRAM Buffering for ToF LIDAR
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Solution Overview
Problem
Time-of-flight (ToF) lidar systems face inefficiencies in memory resource utilization due to sparse occupancy of histogram bins, leading to increased memory depth and power consumption, particularly in SPAD arrays, which are challenging to incorporate in smaller pixels with conventional SRAM configurations.
Innovation Solution
Implement pipelined memory storage operations, where initial data storage occurs in a temporary SRAM buffer during a strobe window and subsequent integration into a main SRAM array during the remainder of the emitter pulse cycle, decoupling sampling and integration processes to optimize memory operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional SRAM configurations are used in SPAD pixels for histogramming, then memory storage capability is provided, but device complexity and layout difficulty increase significantly
Solution Approach 1:
The patent divides the pixel into distinct functional segments: a photodetector region for photon detection, a separate memory region for histogram storage, and control circuitry. This segmentation allows each component to be optimized independently, reducing overall layout complexity while maintaining storage capability.
Solution Approach 2:
The patent utilizes three-dimensional integration by placing the memory array in a different physical layer or spatial arrangement than the photodetector elements. This dimensional separation allows dense memory storage without increasing the two-dimensional pixel footprint, thereby reducing layout difficulty.
2Measurement precision
If memory depth is increased to cover full time range with adequate TDC resolution, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent implements periodic memory refresh and readout cycles synchronized with the laser pulse repetition rate. Instead of continuously powering all memory cells at full depth, the system activates memory regions periodically based on the measurement cycle, reducing average power consumption while maintaining the required time resolution through coordinated sampling.
3Measurement precision
If thousands of time bins are used to form histogram with adequate TDC resolution, then measurement precision is improved, but memory resource utilization efficiency decreases
Solution Approach 1:
The patent implements histogram binning with selective precision: using the full number of time bins only when measurement precision requirements demand it, and reducing active bins for less critical measurements. This partial action approach maintains adequate time resolution for scientific applications while improving memory resource utilization by avoiding unnecessary storage of excessive bin data that would not contribute meaningfully to the measurement.
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 power consumption and memory storage time, allowing for higher bit depth photon counting and improved temporal resolution while addressing layout and power distribution issues in ToF lidar systems.
Implementation Method 1
The initiating charge carrier can be photo-electrically generated by a single incident photon striking the high field region
Implementation Method 2
The high reverse bias voltage generates a sufficient magnitude of electric field such that a single charge carrier introduced into the depletion layer of the device can cause a self-sustaining avalanche via impact ionization
Data Source
AI summary
A Light Detection and Ranging (LIDAR) detector circuit includes a memory device comprising a first memory and a second memory, and at least one control circuit. The at least one control circuit is configured to execute first memory storage operations to store data indicated by detection signals received from one or more photodetector elements in the first memory during a first portion of a time between pulses of an emitter signal output from a LIDAR emitter element, and to execute second memory storage operations to include the data, which was stored in the first memory, in the second memory during a second portion of the time between the pulses of the emitter signal. Related devices and methods of operation are also discussed.