Single-Input Amplifier Capacitive Sensor Noise Reduction
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Solution Overview
Problem
Capacitive sensors in traditional configurations face limitations in power efficiency and noise due to the use of differential input amplifiers, which hinder effective signal amplification and distinguishability between input signals and reference potentials.
Innovation Solution
A capacitive sensing arrangement utilizing a single-input common-source transistor amplifier with a feedback capacitor and bias voltage subtraction, coupled with switching means for phase operation, allowing for reduced noise and current consumption by enabling virtual ground potential and efficient signal amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a differential input amplifier is used in traditional capacitive sensor configurations, then the sensor can establish a virtual ground potential, but the noise at the output increases due to the sum of noise from both non-inverting and inverting inputs
Solution Approach 1:
The patent extracts and eliminates the non-inverting input from the amplifier configuration, transitioning from a differential input amplifier to a single-input amplifier. This removes the noise source associated with the non-inverting input while retaining the essential virtual ground function through bias voltage subtraction, thereby reducing output noise while maintaining signal amplification capability
Solution Approach 2:
The patent introduces a bias voltage as an intermediary element that mediates between the sensor signal and the amplifier input. By subtracting the bias voltage from the sensor signal, the system establishes the necessary virtual ground potential without requiring a non-inverting input, thus eliminating its associated noise while preserving the amplification function
2Reliability
If a differential input amplifier is used to establish virtual ground, then the amplifier can function properly, but the current consumption increases due to the non-inverting input current
Solution Approach 1:
The patent removes the non-inverting input branch from the amplifier configuration, eliminating the current consumption associated with establishing virtual ground through that input. The essential amplifier function is preserved through the single-input configuration with bias voltage subtraction, thereby improving power efficiency while maintaining reliability
Solution Approach 2:
The single-input amplifier configuration allows the amplifier to serve itself by using its own input branch to establish the necessary reference potential through bias voltage subtraction, eliminating the need for a separate non-inverting input current path and thus reducing overall current consumption
3Use of energy by moving object
If a single-input amplifier is used instead of a differential input amplifier, then noise and current consumption are reduced, but the amplifier cannot distinguish between input signal and reference potential
Solution Approach 1:
The patent applies preliminary action by subtracting the bias voltage from the sensor signal before it reaches the amplifier input. This pre-processing step establishes the reference potential in advance, allowing the single-input amplifier to clearly distinguish between the input signal component and the reference potential, thereby resolving the signal distinguishability issue while maintaining power efficiency
Solution Approach 2:
The bias voltage acts as an intermediary that separates the input signal from the reference potential. By subtracting this intermediary bias voltage from the sensor signal, the system enables the single-input amplifier to process only the differential signal component, thus achieving both power efficiency and signal distinguishability
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 achieves a 3 dB improvement in noise reduction and halves power consumption by effectively amplifying sensor signals while maintaining a stable output voltage, independent of bias voltage values.
Implementation Method 1
a feedback capacitor (CF) coupled between the output and the input
Implementation Method 2
at least one of first and second capacitors is adapted to change its capacitance in response to a physically measurable value such as acceleration, pressure or distance
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
In one embodiment a Capacitive sensing arrangement has a capacitive sensor (CapS) for providing a sensor signal (Sin), and a charge amplifier circuit comprising an input (In) which is connected to the capacitive sensor (CapS), a single-input amplifier (A1) with an amplifier input (Ina) and an output (Out) to provide an output voltage (Vout) as a function of the sensor signal (Sin), means (M) for providing a bias voltage (Vref) coupled between the input (In) an the amplifier input (Ina), and a feedback capacitor (CF) coupled between the output (Out) and the input (In). Furthermore, a method for capacitive sensing is defined.