Differential Capacitive Readout Circuit for Flicker Noise Suppression
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Solution Overview
Problem
Current differential capacitive sensors face challenges with low-frequency and weak sensing signals, which are prone to flicker noise, making it difficult to achieve high accuracy and competitiveness in the market.
Innovation Solution
A reading device for capacitive sensing elements is designed, comprising a modulation signal generator, a differential capacitive sensing element, a charge-to-voltage conversion circuit, a phase adjustment circuit, a demodulator, and a low-pass filter. This device modulates the sensing signal to a higher frequency, demodulates it back to the original frequency, and filters out noise to improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the sensing signal is kept at low frequency to maintain simplicity, then the system complexity is reduced, but the signal becomes susceptible to flicker noise and measurement precision deteriorates
Solution Approach 1:
The patent changes the frequency parameter of the sensing signal by modulating it to a higher frequency band. This resolves the contradiction by allowing the system to maintain simplicity while avoiding the low-frequency flicker noise that degrades measurement precision. The modulation technique transforms the signal without requiring complex hardware modifications.
Solution Approach 2:
The patent introduces a modulation signal as an intermediary carrier to transfer the sensing information to a higher frequency band. This intermediary approach allows the system to benefit from high-frequency noise characteristics while keeping the original low-frequency sensing mechanism simple, thus resolving the contradiction between system complexity and measurement precision.
2Measurement precision
If the sensing signal is modulated to higher frequency to avoid flicker noise, then measurement precision is improved, but device complexity increases due to additional modulation and demodulation circuits
Solution Approach 1:
The patent employs periodic modulation signals to shift the sensing signal to higher frequency bands where flicker noise is reduced. This periodic action is implemented through standard modulation techniques that, while adding circuits, use well-established methods to achieve noise reduction. The demodulation process recovers the original signal while filtering out high-frequency noise components.
Solution Approach 2:
The patent implements feedback mechanisms in the demodulation stage to recover the original sensing signal while eliminating the modulation carrier and associated noise. The feedback control in the demodulator ensures that the signal-to-noise ratio is optimized, justifying the additional circuit complexity by delivering measurable performance improvements.
3Measurement precision
If flicker noise is filtered out using low-pass filtering, then measurement precision is improved, but signal processing time increases and productivity decreases
Solution Approach 1:
The patent performs preliminary frequency modulation of the sensing signal before it enters the filtering stage. By pre-modulating the signal to a higher frequency, the subsequent low-pass filtering operation becomes more efficient because the noise separation is already partially accomplished in the frequency domain. This preliminary action reduces the processing burden during the filtering stage, maintaining faster processing speeds while improving accuracy.
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 proposed solution effectively enhances the signal-to-noise ratio and improves the accuracy of capacitive sensing, addressing the limitations of existing differential capacitive sensors by filtering out flicker noise and modulating signals to higher frequency bands.
Implementation Method 1
A modulation signal is input into a common node of the differential capacitive sensing element to modulate a sensing signal
Implementation Method 2
a charge-to-voltage conversion circuit, configured to convert the charge signal into a voltage signal
Implementation Method 3
A low-pass filter is connected to the demodulator and configured to filter the voltage signal that is demodulated, and output the filtered voltage signal as a read signal
Data Source
AI summary
A reading device for capacitive sensing element comprises a differential capacitive sensing element, a modulator, a charge-voltage conversion circuit, a phase adjustment circuit, a demodulator and a low-pass filter. The modulator outputs a modulation signal to the common node of the capacitive sensing element and modulates the output signal of the capacitive sensing element. The two input terminals of the charge-to-voltage conversion circuit are connected to two non-common nodes of the capacitive sensing element. The charge-to-voltage converter read the output charge of the capacitive sensing element and convert it into a voltage signal. The modulator generates a demodulation signal through the phase adjustment circuit. The demodulator receives the demodulation signal from the phase adjustment circuit and demodulates the output of the charge-to-voltage conversion circuit. The low-pass filter is connected to the output of the demodulator for filtering the demodulated voltage signal to output the read signal.