Capacitive Sensor Circuit With Digital Common-Mode Voltage Control
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Solution Overview
Problem
Existing capacitive sensors face challenges in maintaining high capacitance-voltage conversion gain and output amplitude range while minimizing power consumption, as increased capacitance-voltage conversion gain often leads to decreased output amplitude range and inaccurate common mode voltage detection due to analog circuit adjustments and temperature fluctuations.
Innovation Solution
A capacitive sensor design incorporating first and second detection capacitors, feedback capacitors, an A/D converter, and digitally controlled variable capacitors that adjust capacitance values to control common mode voltage levels, allowing for digital control of capacitance changes and accurate signal detection without continuous analog circuit operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitance-voltage conversion gain is increased, then the noise specification is improved, but the amplitude range of the output voltage is remarkably decreased
Solution Approach 1:
The patent replaces the traditional analog common mode voltage adjustment circuit with a digital control system. The common mode voltage detection and adjustment functions are implemented through digital signal processing rather than continuous analog circuit operation, allowing for precise control of the output voltage amplitude range while maintaining high capacitance-voltage conversion gain
Solution Approach 2:
The patent dynamically adjusts the common mode voltage level based on detected output signal characteristics. By changing the common mode voltage parameter in response to signal conditions, the system maintains optimal amplitude range and prevents output saturation, thereby preserving productivity while enabling high conversion gain
2Reliability
If a common mode voltage adjustment analog circuit is added, then the capacitance-voltage conversion gain and amplitude range are secured, but power consumption is increased
Solution Approach 1:
The patent implements periodic sampling and digital processing of the common mode voltage rather than continuous analog adjustment. The system detects the common mode voltage at specific intervals and makes discrete adjustments based on digital signal analysis, significantly reducing power consumption compared to continuous analog circuit operation while maintaining reliable capacitance-voltage conversion
Solution Approach 2:
The patent substitutes the continuous operating analog common mode voltage adjustment circuit with a digital control system that operates periodically. This replacement eliminates the continuous power consumption of analog circuits while achieving the same functional goal of maintaining optimal conversion gain through digital signal processing and periodic correction
3Productivity
If the common mode voltage is adjusted through analog circuit, then the output amplitude range is maintained, but measurement accuracy deteriorates due to temperature fluctuation
Solution Approach 1:
The patent replaces the temperature-sensitive analog common mode voltage adjustment circuit with a digital control system. The digital implementation is less susceptible to temperature fluctuations and drift, providing more stable and accurate common mode voltage detection and adjustment over varying temperature conditions while maintaining the required output amplitude range
Solution Approach 2:
The patent implements a feedback mechanism where the common mode voltage is continuously detected and used to adjust the output signal. This closed-loop digital feedback system compensates for temperature-induced variations by dynamically adjusting the common mode voltage based on real-time detection, thereby maintaining both amplitude range and measurement precision under varying temperature 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
This design enables low power consumption and accurate common mode voltage adjustment, maintaining a wide input signal range and high capacitance-voltage conversion gain, reducing the impact of temperature fluctuations on sensor accuracy.
Implementation Method 1
first and second digitally controlled variable capacitors having capacitance values which are controlled by the digital control unit
Data Source
AI summary
The present invention is directed to a CV conversion amplifier which is small in current consumption and capable of securing a sufficient capacitance-voltage conversion gain and a sufficient amplitude range of an output voltage and a capacitive sensor using the same which is low power consumption, low in noise, and wide in an input signal allowable range. A capacitive sensor includes first and second detection capacitors, a CV conversion circuit includes first and second feedback capacitors and obtains a voltage based on capacitance values of the first and second feedback capacitors, an AD converter performs analog digital conversion on an input voltage and obtains a digital signal, a digital control unit receives the digital signal as an input, and first and second digitally controlled variable capacitors have capacitance values that are controlled by the digital control unit.