R-2R ADC Circuit Layout for Compact Low-Noise Endoscope Imaging
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Solution Overview
Problem
The challenge in reducing the size of AD conversion circuits for imaging devices, such as those used in endoscope systems, is exacerbated by the exponential increase in capacitance area with increasing resolution, leading to difficulties in miniaturizing both the AD conversion circuit and the imaging device, and resulting in degraded image quality due to noise superimposition.
Innovation Solution
The proposed AD conversion circuit incorporates a comparison circuit with capacitance elements and a DA conversion circuit featuring an R-2R ladder structure, along with a voltage output circuit, which adjusts resistance values based on operational modes to optimize circuit performance and reduce size, while maintaining high-speed conversion capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a capacitance element is used in the AD conversion circuit to reduce power consumption, then power consumption is reduced, but the area of the capacitance element exponentially increases with resolution, making it difficult to reduce the size of the AD conversion circuit and imaging device
Solution Approach 1:
The patent changes the fundamental parameter from capacitance-based storage to resistance-based storage. By using a resistance element instead of a capacitance element to hold the signal voltage, the circuit avoids the exponential area increase that occurs with capacitance elements as resolution increases, while still achieving low power consumption because no continuous charging current is needed.
Solution Approach 2:
The patent substitutes the electrical capacitance mechanism with a resistance-based mechanism. Instead of using the electrostatic storage property of capacitance elements, the invention uses the electrical resistance property of resistance elements to hold signal voltages, fundamentally changing the physical mechanism used for signal storage.
2Area of stationary object
If the AD conversion circuit size is reduced to miniaturize the imaging device, then the imaging device size is reduced, but the conversion time increases, degrading image quality due to noise superimposition
Solution Approach 1:
The patent makes the resistance value dynamic by using a voltage output circuit that changes the resistance value based on operational mode. During signal sampling and holding, the resistance is set to a first value optimized for signal retention. During comparator operation, the resistance is changed to a second value optimized for conversion speed, allowing the circuit to achieve both fast conversion and accurate signal holding without increasing overall size.
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 configuration allows for a compact AD conversion circuit that effectively reduces noise and enhances image quality by minimizing the time required for signal sampling and holding, enabling high-speed and precise analog-to-digital conversion.
Implementation Method 1
The first capacitance element includes a first terminal to which a first signal is input and a second terminal electrically connected to the first DA conversion circuit and the first voltage output circuit. The first capacitance element is configured to hold the first signal.
Implementation Method 2
The second capacitance element includes a first terminal to which a second signal is input and a second terminal connected to a first voltage source. The second capacitance element is configured to hold the second signal.
Implementation Method 3
The comparator includes a first input terminal connected to the first terminal of the first capacitance element and includes a second input terminal connected to the first terminal of the second capacitance element. The comparator is configured to output a signal that represents a result of comparing a first voltage of the first input terminal with a second voltage of the second input terminal.
Implementation Method 4
In an AD conversion circuit using a resistance element, it is possible to constitute at least part of a DA conversion circuit by using an R-2R ladder circuit. In this way, it is possible to suppress area increase, compared to a resistance-parallel type AD conversion circuit.
Data Source
AI summary
An AD conversion circuit includes a comparison circuit, a first DA conversion circuit including a plurality of resistance elements, and a first voltage output circuit. A comparator of the comparison circuit outputs a signal that represents a result of comparing a first voltage of a first input terminal with a second voltage of a second input terminal. A first combined resistance value of the first DA conversion circuit and the first voltage output circuit seen from a second terminal of the first capacitance element is a first value when the first capacitance element holds a first signal. The first combined resistance value is a second value when the comparator compares the first voltage with the second voltage. The first value is less than the second value.