Capacitive Sensing Circuit With Signal Extraction to Avoid ADC Saturation
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Solution Overview
Problem
Conventional capacitance sensing circuits face challenges in accurately sensing capacitance changes due to tiny capacitance variations, leading to small signal variations and increased complexity and cost from requiring large dynamic range and high resolution analog-to-digital converters, where the significant variable signal for capacitance sensing is often overlooked.
Innovation Solution
A capacitance sensing circuit with a front-end circuit including an active component, a subtracting and summing circuit, and a capacitance judging circuit, which enhances noise resistance and signal-to-noise ratio, restricts the variation range of summing signals, and prevents analog-to-digital converter saturation, thereby reducing the complexity and cost while improving precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an analog-to-digital converter with large dynamic range and high resolution is used to parse the analog output signal, then the measurement precision of capacitance variation is improved, but the device complexity and manufacturing cost are increased
Solution Approach 1:
The patent segments the analog output signal into two separate signals: a fixed signal component and a variable signal component. The variable signal component, which contains the capacitance variation information, is extracted and processed separately using a simpler analog-to-digital converter. This segmentation allows the use of a low-resolution converter for the variable signal while the fixed signal is handled differently, thereby reducing the requirements for converter precision and complexity.
Solution Approach 2:
The patent extracts the variable signal component from the complete analog output signal. By isolating only the variable portion that contains the capacitance variation information, the system can process this extracted signal with a simpler converter that has lower dynamic range and resolution requirements, thus reducing device complexity while maintaining measurement precision for the capacitance variation.
2Measurement precision
If an analog-to-digital converter with large dynamic range and high resolution is used, then the measurement precision is improved, but the manufacturing cost is increased
Solution Approach 1:
The patent segments the analog output signal into a fixed signal component and a variable signal component. The variable signal component is extracted and processed using a simpler, lower-cost analog-to-digital converter. This segmentation enables the use of cost-effective converters with reduced precision specifications while still achieving accurate capacitance variation measurement, thereby lowering manufacturing costs.
Solution Approach 2:
The patent extracts the variable signal component that contains the capacitance variation information from the complete analog output signal. This extracted variable signal can be processed by a simpler, more cost-effective analog-to-digital converter, reducing the need for expensive high-resolution converters and thus lowering the overall manufacturing cost of the system.
3Loss of information
If the analog output signal is parsed by a high-resolution analog-to-digital converter, then the signal analysis capability is improved, but the variable signal significant to capacitance sensing is not properly parsed due to consumption of dynamic range on fixed signal
Solution Approach 1:
The patent segments the analog output signal into a fixed signal component and a variable signal component. By separating these components, the variable signal containing capacitance variation information can be processed independently with appropriate signal processing techniques, ensuring that the dynamic range of the analog-to-digital converter is optimally utilized for the variable signal rather than being dominated by the fixed signal component.
Solution Approach 2:
The patent extracts the variable signal component from the complete analog output signal. This extraction ensures that the variable signal, which contains the capacitance variation information, is isolated and can be processed with an analog-to-digital converter configured appropriately for its specific characteristics, preventing the fixed signal from consuming the available dynamic range and improving the reliability of capacitance sensing.
Data Source
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AI summary
A capacitance sensing circuit includes: a front-end circuit, a first subtracting and summing circuit and a capacitance judging circuit; wherein the front-end circuit is coupled to the detection circuit; the first subtracting and summing circuit is coupled between the front-end circuit and the capacitance judging circuit, and includes: a subtracting unit; a summing unit, coupled to the subtracting unit; a first converter, coupled between the summing unit and the capacitance judging unit; and a second converter, coupled between the first converter and the subtracting unit; and the capacitance judging circuit is configured to judge a capacitance change of the detection capacitor. According to the present application, resistance against noise is improved by using the front-end circuit including an active component, and a variation range of summing signals is restricted by using a subtracting and summing circuit. In this way, an analog-to-digital converter is prevented from entering a saturation state, and a high signal-to-noise ratio is achieved.