Capacitive Amplifier Circuit for Accurate Sensor Voltage Detection
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Solution Overview
Problem
Existing sensor devices that detect voltage changes in electrostatic capacitance suffer from low detection accuracy due to noise amplification, particularly when using a source follower for amplification.
Innovation Solution
A sensor device incorporating a capacitive amplifier circuit with operational amplifiers, capacitors, and switch configurations to selectively function as either a capacitive amplifier or voltage follower, reducing noise and improving detection accuracy by amplifying signals based on capacitance ratios and resetting voltages to reference potentials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a source follower is used to amplify the detection voltage, then the detection voltage is amplified, but noise is also amplified and detection accuracy deteriorates
Solution Approach 1:
The amplification process is divided into two distinct stages: first, the capacitive amplifier circuit amplifies the detection voltage based on the capacitance ratio between first and second capacitors; second, the source follower amplifies the output from the capacitive amplifier. This segmentation allows each stage to perform its function optimally while the noise reduction mechanism operates independently in the first stage
Solution Approach 2:
The reset switch performs preliminary action by resetting the detection electrode to reference potential before the amplification process begins. This preliminary reset eliminates offset voltages and prepares the system in a known state, preventing noise and offset from being amplified along with the detection voltage in subsequent stages
2Power
If the detection voltage is amplified in a subsequent stage, then the signal level is increased, but offset and switching noise are also amplified
Solution Approach 1:
The reset switch performs preliminary action by resetting the detection electrode to reference potential before amplification. This eliminates offset voltages at the source, preventing them from being amplified in subsequent stages
Solution Approach 2:
The changeover switch dynamically transitions the capacitive amplifier circuit between capacitive amplification mode and voltage follower mode. This dynamic switching allows the system to optimize performance for different operational requirements while controlling noise through proper timing and sequence
3Measurement precision
If a capacitive amplifier circuit is used to amplify the detection voltage, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The capacitive amplifier circuit is designed to perform multiple functions: it can operate as a capacitive amplifier for high-precision detection, as a voltage follower for buffering, and can be reset to reference potential. The same circuit components (operational amplifier, first capacitor, second capacitor, reset switch, changeover switch) serve multiple purposes, reducing the need for separate dedicated circuits for each function
Solution Approach 2:
The reset function and amplification function are merged into a single integrated circuit structure. The reset switch and changeover switch are incorporated directly into the capacitive amplifier circuit, allowing the same physical components to perform both reset and amplification operations at different times, thereby reducing overall device complexity
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 effectively reduces noise and enhances detection accuracy by amplifying signals while minimizing offset and switching noise, improving the overall performance of the sensor device.
Implementation Method 1
a detection electrode opposing an external electrode to which a predetermined voltage is applied, and configured to generate a voltage corresponding to a change in electrostatic capacitance
Implementation Method 2
a capacitive amplifier circuit having an operational amplifier, a first capacitor, and a second capacitor connected between an output terminal and an inverting input terminal of the operational amplifier, and the first capacitor connected in series to the second capacitor, the capacitive amplifier circuit being configured to detect the voltage generated in the detection electrode and output a detection signal obtained by amplifying the voltage generated in the detection electrode based on a capacity ratio between the first capacitor and the second capacitor
Data Source
AI summary
A sensor device includes a detection electrode opposing an external electrode, and generating a voltage corresponding to a change in capacitance; a capacitive amplifier circuit having a first capacitor and a second capacitor, and configured to detect the voltage generated in the detection electrode, and output a detection signal obtained by amplifying the voltage generated in the detection electrode based on a capacitance ratio between the first capacitor and the second capacitor; a reset switch configured to reset the voltage of the detection electrode to a reference potential; a changeover switch configured to switch the capacitive amplifier circuit between a capacitive amplifier and a voltage follower; a second changeover switch configured to disconnect the first capacitor from the capacitive amplifier circuit; and a second reset switch configured to reset a voltage of the first capacitor to the reference potential.