Solid-State Imaging Element Up-Down Counter Circuit Scale Reduction
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Solution Overview
Problem
Conventional solid-state imaging elements with high sensitivity SPADs face challenges in reducing circuit scale for distance measurement, particularly when using the time of flight (ToF) method, which requires multiple counters per pixel, leading to increased complexity and potential overflow issues with high light brightness.
Innovation Solution
A solid-state imaging element employing a pulse signal generation section with an avalanche photodiode and a quench circuit, along with up-down counters that perform up counting and down counting based on phase-shifted clock signals during light-on and light-off periods, reducing the number of counters needed and enabling distance measurement using the ToF method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple counters are added for every pixel to perform distance measurement by ToF method, then distance measurement capability is improved, but circuit scale increases
Solution Approach 1:
The patent combines multiple counting functions into a single counter by using phase-shifted clock signals to control the counter's operation. The same counter performs different counting tasks (e.g., photon counting vs. distance measurement) by switching the clock signal phase, eliminating the need for separate counters for each function and thus reducing circuit scale.
Solution Approach 2:
The counter is designed to serve multiple purposes: it can count photons during light emission periods and measure distance during light reception periods by simply changing the clock signal phase. This multi-functional design allows one counter to replace what would traditionally require multiple specialized counters, reducing overall circuit complexity.
2Reliability
If up counting is performed during light-on period and down counting during light-off period, then counter overflow is reduced, but requires phase-shifted clock signals
Solution Approach 1:
The system dynamically switches between up-counting and down-counting modes by adjusting the phase of the clock signal based on the operational state (light emission vs. light reception). This dynamic mode switching allows the counter to adapt its behavior to prevent overflow while using a single counter resource, and the phase-shifted clock generation is achieved through standard phase-locked loop circuits.
3Device complexity
If single counter is used for both photon counting and distance measurement, then circuit scale is reduced, but measurement precision may be affected
Solution Approach 1:
The system uses periodic phase-shifted clock signals to alternately control up-counting and down-counting operations. By synchronizing the counting operations with periodic light emission and reception cycles, the single counter can accurately measure both photon counts and distance without interference, maintaining measurement precision while using minimal circuit resources.
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
The solution reduces the circuit scale per pixel, minimizes counter overflow, and improves common-mode rejection ratio, allowing for efficient distance measurement while maintaining dynamic range and reducing wire charge/discharge capacity.
Implementation Method 1
an avalanche photodiode that converts incident light including reflected light of irradiation light radiated during a predetermined light-on period into a photocurrent
Implementation Method 2
an avalanche photodiode that converts incident light including reflected light of irradiation light radiated during a predetermined light-on period into a photocurrent and multiplies the photocurrent
Implementation Method 3
a quench circuit that generates a pulse signal on the basis of the above-described multiplied photocurrent
Implementation Method 4
an up-down counter that performs one of up counting and down counting each time the above-described pulse signal is generated during the above-described light-on period, and performs another of the above-described up counting and the above-described down counting each time the above-described pulse signal is generated during a light-off period
Data Source
AI summary
In a solid-state imaging element that measures a distance, a circuit scale is reduced. The solid-state imaging element includes a pulse signal generation section and an up-down counter. The pulse signal generation section is provided with an avalanche photodiode that converts incident light including reflected light of irradiation light radiated during a predetermined light-on period into a photocurrent and multiplies the photocurrent and a quench circuit that generates a pulse signal on the basis of the multiplied photocurrent. The up-down counter performs one of up counting and down counting each time the pulse signal is generated during the light-on period, and performs another of the up counting and the down counting each time the pulse signal is generated during a light-off period that does not correspond to the light-on period.