Capacitance Detection Circuit Noise Reduction via Dummy Capacitor
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Solution Overview
Problem
Existing capacitance detection circuits face challenges in reducing noise gain, particularly when detecting small capacitance changes, due to the limitations in reducing the capacitance of the reference capacitor without compromising noise reduction.
Innovation Solution
A capacitance detection circuit is designed with a carrier signal generating circuit, an operational amplifier, a dummy capacity connected in parallel, and a carrier signal conditioning circuit that inverts and adjusts the carrier signal phase and gain to reduce noise gain, while also improving the signal-to-noise ratio through a low pass filter and A/D conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the capacitance of the reference capacitor is reduced to reduce noise gain, then noise reduction is improved, but the capacitance cannot be reduced further due to circuit stability requirements
Solution Approach 1:
A dummy capacitor is introduced as an intermediary element connected to the inverting input terminal of the operational amplifier. This dummy capacitor, when driven by an inverted carrier signal, acts as a mediator to cancel the noise gain contribution of the reference capacitor without requiring the reference capacitor itself to be reduced in value, thereby maintaining circuit stability while reducing noise.
Solution Approach 2:
The invention applies preliminary anti-action by introducing a counterbalancing signal through the dummy capacitor that预先 (in advance) cancels the noise gain effect. The carrier signal conditioning circuit generates an inverted carrier signal that drives the dummy capacitor to produce a signal that opposes and neutralizes the noise contribution before it can affect the output, allowing the reference capacitor to maintain its stabilizing value.
2Measurement precision
If the capacitance detection circuit is designed for high resolution detection, then measurement precision is improved, but circuit noise increases
Solution Approach 1:
The dummy capacitor serves as an intermediary that selectively affects noise signals while leaving the measurement signal intact. By driving the dummy capacitor with an inverted carrier signal, the circuit creates a noise cancellation mechanism that improves measurement precision without being compromised by circuit noise.
Solution Approach 2:
The invention changes the parameter of noise gain by introducing the dummy capacitor with a specific capacitance value and driving it with a conditioned carrier signal. This parameter change allows the circuit to achieve high resolution detection by reducing the noise gain factor while maintaining the signal integrity for precise capacitance measurement.
3Device complexity
If MEMS sensor is combined with capacitance detection circuit to achieve cost/size reduction, then device complexity is reduced, but noise detection capability deteriorates
Solution Approach 1:
The dummy capacitor acts as a noise-cancelling intermediary within the integrated MEMS sensor system. This intermediary element compensates for the noise that would otherwise be exacerbated by the close integration of MEMS and capacitance detection circuitry, enabling compact design without sacrificing noise performance.
Solution Approach 2:
The carrier signal conditioning circuit provides feedback by generating an inverted carrier signal that drives the dummy capacitor. This feedback mechanism continuously counteracts noise signals in the integrated system, maintaining noise detection capability while achieving the cost and size benefits of MEMS integration.
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 gain and enhances the signal-to-noise ratio, enabling accurate detection of small capacitance changes, thereby improving the overall performance of the capacitance detection circuit.
Implementation Method 1
an inverting input terminal is imaginary-shorted to the ground by connecting a non-inverting input side of the operational amplifier to the ground
Data Source
AI summary
A capacitance detection circuit inhibits noise. The capacitance detection circuit detects a change in capacitance between a pair of electrodes of a physical quantity sensor, with these electrodes generating the change in capacitance in response to a change in physical quantity. The capacitance detection circuit has a carrier signal generating circuit that supplies a carrier signal to one of the electrodes, an operational amplifier that has an inverting input terminal to which the other one of the electrodes is input, a dummy capacity that is connected in parallel to the pair of electrodes, and a carrier signal conditioning circuit that inverts a phase of a carrier signal supplied from the carrier signal generating circuit to the dummy capacity and adjusts a gain to inhibit the dummy capacity.