Capacitance Detection Circuit Using Differential Front-Ends
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Solution Overview
Problem
Existing self-capacitance detection methods have low sensitivity due to high self-capacitance values, which makes it difficult to accurately detect capacitance values, and increasing the number of cancel capacitors to improve sensitivity is costly and non-integratable.
Innovation Solution
A capacitance detection circuit that includes reference capacitors and front-end circuits for converting capacitance signals into differential voltage signals, processed by a circuit to determine the capacitance values of multiple capacitors, improving sensitivity without significantly increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of cancel capacitors is increased to improve sensitivity, then the sensitivity of capacitance detection is improved, but the device complexity and cost increase significantly
Solution Approach 1:
The patent segments the capacitance detection function into multiple front-end circuits, where each circuit handles a specific capacitor. This allows parallel processing of multiple capacitance signals without requiring additional cancel capacitors, thereby improving sensitivity while maintaining device complexity at acceptable levels.
Solution Approach 2:
The patent transitions from a single-dimensional detection approach (using only cancel capacitors) to a multi-dimensional approach by introducing both first front-end circuits for direct capacitance conversion and second front-end circuits for differential measurement. This dimensional expansion enables accurate capacitance detection without proportionally increasing the number of cancel capacitors.
2Measurement precision
If the number of cancel capacitors is increased to improve sensitivity, then the sensitivity of capacitance detection is improved, but the cost increases excessively
Solution Approach 1:
The patent designs front-end circuits that can serve multiple functions: converting capacitance to voltage, performing differential measurement, and enabling touch detection. This multi-functionality reduces the need for separate cancel capacitors and associated components, thereby improving sensitivity while controlling manufacturing costs.
Solution Approach 2:
The patent changes the operating parameters of the detection circuit by using programmable gain amplifiers (PGA) that can adjust their gain based on the detected capacitance value. This dynamic parameter adjustment allows the system to achieve high sensitivity across a wide range of capacitance values without requiring multiple fixed-value cancel capacitors, thus reducing cost.
3Quantity of substance
If self-capacitance is increased, then the capacitance value for touch detection is improved, but the sensitivity of detection becomes lower
Solution Approach 1:
The patent inverts the traditional approach by not trying to reduce self-capacitance to improve sensitivity, but instead accepting high self-capacitance values and using front-end circuits with programmable gain amplifiers that can adapt to and accurately measure large capacitance values. This inversion allows both high self-capacitance and high detection sensitivity to coexist.
Solution Approach 2:
The patent introduces dynamic gain adjustment through programmable gain amplifiers that can change their amplification factor based on the detected capacitance value. This dynamic adaptation allows the system to maintain high sensitivity regardless of whether the self-capacitance is large or small, resolving the contradiction between capacitance magnitude and detection sensitivity.
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 enhances the sensitivity of capacitance detection by using differencing and recovery processes, allowing for accurate capacitance value determination while maintaining cost-effectiveness.
Implementation Method 1
a first front end circuit outputs, to a processing circuit, a first differential signal of voltages corresponding to two connected capacitors to be detected
Implementation Method 2
converting capacitance signals of the capacitors to be detected into first voltage signals
Implementation Method 3
performing differencing on the first voltage signals
Data Source
AI summary
Provided are a capacitance detection circuit (200). The capacitance detection circuit (200) is used for detecting capacitances of N capacitors to be detected, and includes: a reference capacitor, at least N−1 first front end circuits (210) for converting capacitance signals of the capacitors to be detected into first voltage signals and performing differencing on the first voltage signals, at least one second front end circuit (220) for converting capacitance signals of a capacitor to be detected and a reference capacitor into second voltage signals and performing differencing on the second voltage signals, and a processing circuit (230); and the processing circuit (230) determines a capacitance value of each of the N capacitors to be detected according to a first differential signal output by each of the first front end circuits (210) and a second differential signal output by each of the second front end circuits (220).