Analog Front End Circuit for Capacitance Measurement
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Solution Overview
Problem
Conventional analog front end circuits for measuring capacitance in touchscreens suffer from wide-band noise sampling issues, leading to increased power consumption and reduced sensitivity due to the lack of noise filtering, and require tunable band-pass filters that are not adaptable to different noise spectrums.
Innovation Solution
An analog front end circuit utilizing coherent detection with a programmable impedance element and correlator for synchronous demodulation, which generates an excitation signal modulated by the capacitance, filters noise through integration, and adapts to different frequency responses by varying the excitation signal frequency without altering the low-noise amplifier or mixer components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional analog front end circuits are used for capacitance measurement, then the circuit structure is simple, but wide-band noise sampling occurs leading to increased power consumption and reduced sensitivity
Solution Approach 1:
The patent implements periodic sampling of the capacitance signal at a specific frequency, using a sampling clock that operates periodically to capture the modulated capacitance signal. This periodic action allows the system to integrate noise over time while maintaining sensitivity to the periodic capacitance variations, thereby improving measurement precision while managing power consumption through controlled sampling intervals.
Solution Approach 2:
The patent changes the sampling frequency parameter to match the modulation frequency of the capacitance signal. By adjusting the sampling frequency to be synchronized with the excitation signal frequency, the system achieves coherent detection that maximizes signal-to-noise ratio. This parameter optimization allows accurate capacitance measurement with reduced power consumption compared to continuous wide-band sampling.
2Measurement precision
If conventional analog front end circuits without noise filtering are used, then the circuit complexity is low, but noise and interference are not rejected leading to reduced measurement accuracy
Solution Approach 1:
The patent uses periodic integration over multiple cycles of the excitation signal to reject noise and interference. By integrating the sampled signal over a period that is an integer multiple of the excitation signal period, the system achieves noise rejection through coherent integration, improving measurement accuracy without requiring complex filtering circuits.
Solution Approach 2:
The patent implements continuous integration of the capacitance signal over multiple sampling periods, maintaining the useful signal while averaging out random noise and interference. This continuous integration process improves measurement accuracy by accumulating signal energy while noise cancels out over time, achieving better performance without adding complex discrete filtering stages.
3Adaptability or versatility
If tunable band-pass filters are used to adapt to different noise spectrums, then the adaptability to various noise spectrums is improved, but the device complexity and power consumption increase
Solution Approach 1:
The patent achieves adaptability to different noise spectrums by changing the sampling frequency parameter to match different excitation frequencies, rather than using complex tunable band-pass filters. The integration period is adjusted as a parameter to optimize noise rejection for different operating conditions. This parameter-based adaptation maintains circuit simplicity while providing versatility across different noise environments.
Solution Approach 2:
The patent implements a universal integration-based noise rejection mechanism that works across different excitation frequencies and noise spectrums without requiring frequency-specific filter circuits. The same integrator circuit can adapt to different operating conditions by adjusting the integration period and sampling frequency, providing multi-functional noise rejection capability without increasing device complexity.
4Measurement precision
If wide-band sampling is performed without noise filtering, then the signal processing is simple, but the signal-to-noise ratio is reduced leading to lower measurement sensitivity
Solution Approach 1:
The patent employs periodic sampling synchronized with the excitation signal frequency to improve the signal-to-noise ratio. By sampling at specific phases of the excitation cycle and integrating over complete periods, the system coherently accumulates the mod capacitance signal while incoherent noise averages out, achieving high signal-to-noise ratio with relatively simple periodic signal processing.
Solution Approach 2:
The patent implements continuous coherent integration of the capacitance signal over multiple excitation cycles, maintaining high signal-to-noise ratio through continuous accumulation of signal energy. This continuous integration process improves measurement sensitivity by systematically processing the signal over time without requiring complex discrete filtering operations at each stage.
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 solution effectively rejects noise and interference, reduces power consumption, and enhances the signal-to-noise ratio while maintaining high sensitivity and adaptability to various noise spectrums, thereby improving the accuracy of capacitance measurement in touchscreens.
Implementation Method 1
Analog front end circuits utilizing coherent detection with a programmable impedance element and correlator for synchronous demodulation
Implementation Method 2
generates an excitation signal modulated by the capacitance, filters noise through integration
Data Source
AI summary
A system includes a signal generator and a correlator. The signal generator outputs a first signal to a first end of a capacitance to be measured. The correlator is connected to an output of the signal generator that outputs the first signal and to a second end of the capacitance. The correlator receives the first signal from the output of the signal generator and receives a second signal from the second end of the capacitance. The correlator correlates the first signal and the second signal and generates an output signal based on a correlation between the first signal and the second signal. The output signal is proportional to a capacitance value of the capacitance.