SPAD Pixel Bit Optimization for ToF Distance Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing distance measuring devices using Time of Flight (ToF) sensors with multiple SPAD elements require additional bits to represent pixel values, leading to unnecessary circuit expansion and power consumption due to inefficient use of computing elements and wiring lines.
Innovation Solution
A light receiving device with a selecting section that groups SPAD elements into pixels, an addition section that generates 2N-1 binary values from individual detection values, and a computing section that calculates an N-bit pixel value by adding these values, optimizing the number of bits required for distance measurement computations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If one pixel is constituted by n SPAD elements where n is a power of 2, then the pixel value can be represented with sufficient range, but the number of bits required increases by one bit compared to n-1 elements, leading to waste of computing elements and wiring lines
Solution Approach 1:
The patent changes the parameter of SPAD element count from conventional power-of-2 values to values of the form 2^N - 1 (e.g., 1, 3, 7, 15, 31 elements). This parameter change allows the pixel value range to exactly match the representable range with N bits, eliminating the need for one extra bit and reducing circuit scale while maintaining sufficient dynamic range for distance measurement
2Quantity of substance
If one pixel is constituted by n SPAD elements where n is a power of 2, then the pixel value range is sufficient, but the number of bits required increases by one bit, leading to increased power consumption
Solution Approach 1:
By changing the SPAD element count to 2^N - 1, the patent reduces the bit width required to represent pixel values from N+1 bits to N bits. This reduction in bit width decreases the power consumption of computing elements and wiring lines while maintaining adequate pixel value range for distance measurement applications
3Measurement precision
If additional bits are used to represent pixel values, then the dynamic range is sufficient, but computing elements and wiring lines are wasted, increasing circuit scale
Solution Approach 1:
The patent optimizes the relationship between SPAD element count and bit width by setting the number of elements to 2^N - 1. This ensures that the maximum pixel value (2^N - 1) can be exactly represented with N bits, eliminating wasted representation capacity and reducing circuit scale while maintaining measurement precision
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 circuit scale and power consumption by eliminating unnecessary bit representation, achieving efficient distance measurement while minimizing waste in computing elements and wiring lines.
Implementation Method 1
a Time of Flight sensor (ToF sensor) has attracted attention as a distance measuring device that measures a distance by a ToF method
Implementation Method 2
a plurality of single photon avalanche diode (SPAD) elements formed by a complementary metal oxide semiconductor (CMOS) semiconductor integrated circuit technology
Data Source
AI summary
A light receiving device (20) according to one aspect of the present disclosure includes: a light receiving section (22) including a plurality of photon-counting light receiving elements that receives reflected light from a distance measurement target (40) based on irradiation pulsed light from a light source section (10); a selecting section (23) that selects individual detection values of the plurality of light receiving elements at a predetermined time; an addition section (24) that generates 2N−1 binary values (N is a positive integer) from the individual detection values of the plurality of light receiving elements at the predetermined time selected by the selecting section (23) and that calculates an N-bit pixel value by adding up all the 2N−1 binary values; anda computing section (26) that performs computation related to distance measurement using the N-bit pixel value calculated by the addition section (24).