Photon-Counting Photodetection Device Using Carry-Flag Counting
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Solution Overview
Problem
Conventional photodetection devices face limitations in expanding the dynamic range and improving image quality due to saturation of pixel counters, which leads to increased circuit scale and reduced maximum count values.
Innovation Solution
A photodetection device with first and second sensor units, multiplexers, and counters that synchronize pulse signal selection and carry flag handling to extend resolution and dynamic range, particularly in high illuminance conditions, while reducing power consumption and circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution of each counter is increased to expand dynamic range, then image quality is improved, but the circuit scale of the counter is increased
Solution Approach 1:
The patent divides the counting function into multiple counters (first counter and second counter) that operate in parallel. Each counter handles a portion of the counting task, allowing the system to achieve higher resolution without requiring a single large-scale counter. The first counter processes pulse signals while the second counter processes carry flags, segmenting the counting operation to reduce individual counter complexity.
Solution Approach 2:
The patent extends the counting capability by adding a temporal dimension through sequential counting operations. The first counter counts during one phase, and the second counter counts carry flags during another phase, effectively multiplying the resolution capability without increasing the physical size of individual counters. This dimensional approach allows 2N-bit resolution using N-bit counters.
2Adaptability or versatility
If pixel addition is performed to secure linearity of combined signal, then dynamic range is maintained, but maximum count value of each pixel cannot be increased
Solution Approach 1:
The patent implements dynamic switching between counting modes based on illuminance conditions. In low illuminance mode, the system uses standard pixel counting. In high illuminance mode, the system switches to extended resolution mode where the second counter processes carry flags from the first counter, dynamically adapting the counting mechanism to maintain both linearity and extended dynamic range.
Solution Approach 2:
The patent changes the operating parameters of the counting system based on illuminance conditions. By detecting illuminance levels and adjusting the counting mode accordingly, the system can switch between processing pulse signals directly and processing carry flags, thereby changing the effective resolution and maximum count value parameters to match the lighting conditions.
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 device enhances image quality by extending counter resolution and dynamic range, facilitating pixel addition, and reducing power consumption through intelligent signal handling and multiplexing strategies.
Implementation Method 1
Each pixel includes an avalanche photodiode and a recharge transistor that performs recharge to return a cathode potential of the avalanche photodiode to a predetermined potential
Data Source
AI summary
Improved image quality in photodetection devices that count pulses with a counter is disclosed. In one example, a first sensor unit generates a first pulse signal in response to incidence of photons. A second sensor unit generates a second pulse signal in response to incidence of photons. A first counter counts a count value in synchronization with one of a plurality of signals including the first and second pulse signals, and outputs a first digital signal indicating the count value and a first carry flag indicating whether or not overflow has occurred. A second counter counts a count value in synchronization with one of the first carry flag and the second pulse signal, and outputs a second digital signal indicating the count value.