Electric Potential Sensor Input Capacitance Reduction
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Solution Overview
Problem
Existing electric potential sensors face challenges in accurately measuring weak capacitive coupling signals, leading to noise issues and reduced signal-to-noise ratios, particularly in medical and biometric applications where high sensitivity and stability are crucial.
Innovation Solution
The integration of a discrete pre-amplifier stage with low input capacitance, combined with bootstrapping and noise reduction circuits, enhances the signal-to-noise ratio by increasing the amplitude of the measurement signal and reducing noise amplitude, thereby improving measurement accuracy in scenarios with weak capacitive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high input impedance electrometer is used to measure small electrical potentials, then sensitivity is improved, but stability deteriorates
Solution Approach 1:
The electrometer circuit is divided into multiple functional blocks: a first amplifier with high input impedance for signal acquisition, a second amplifier for signal conditioning, and various ancillary circuits (guarding, bootstrapping, neutralisation) that operate independently to address specific stability issues without compromising overall sensitivity
Solution Approach 2:
Ancillary circuits act as intermediary elements between the high input impedance electrometer and the measurement system. These circuits (guarding, bootstrapping, neutralisation) mediate the conflict by providing stability mechanisms that do not directly load the high impedance input, thus preserving sensitivity while ensuring stability
2Measurement precision
If the input capacitance of the sensor is reduced to improve weak capacitive coupling measurement, then signal attenuation is reduced, but noise performance may deteriorate
Solution Approach 1:
The input capacitance is made dynamically adjustable through the switching means, allowing the system to adapt between different measurement modes (contactless with weak coupling versus contact with stronger coupling). This dynamic adjustment optimizes the balance between signal attenuation and noise performance based on the specific measurement requirements
Solution Approach 2:
The system changes the electrical parameter of input capacitance from a fixed value to a variable parameter that can be switched between different states. This parameter change allows optimization for weak capacitive coupling measurements while providing alternative configurations for different measurement scenarios
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 significantly enhances the signal-to-noise ratio, allowing for more accurate and stable non-invasive measurements in applications with weak capacitive coupling, such as biometric and medical sensing, by reducing input capacitance and noise amplitude.
Implementation Method 1
input impedance enhancing means including a bootstrapping circuit for providing a high input impedance to the electric potential sensor
Implementation Method 2
at least one detection electrode arranged for capacitive coupling with a sample under test
Implementation Method 3
the discrete device is a field effect transistor
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention provides an electric potential sensor (28) for the measurement of potentials non-invasively. The sensor comprises at least one detection electrode (12) arranged for capacitive coupling with a sample under test and for generating a measurement signal, and a sensor amplifier (14) adapted to receive the measurement signal as input and to supply an amplified detection signal as output. Input impedance enhancing means (12a, 32, 36, 38, 44) are included for providing a high input impedance to the sensor amplifier for increasing the sensitivity of the electrode to reduced electric potentials, and a discrete pre-amplifier stage (30) is arranged to co-operate with the sensor amplifier to reduce the input capacitance of the amplifier.