Capacitive Detection Circuit Base Capacitance Cancellation
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Solution Overview
Problem
Existing capacitance detection methods suffer from low sensitivity due to high base capacitance and small capacitance variations caused by conductors approaching or touching detection electrodes, making accurate detection challenging.
Innovation Solution
A capacitance detection circuit that cancels the base capacitance before converting the capacitance signal into a voltage signal, using a front end circuit with a cancel circuit and programmable gain amplification to directly reflect capacitance variations, improving sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If base capacitance is high, then the detection electrode can maintain stable electrical properties, but the sensitivity of capacitance detection decreases because capacitance variation becomes smaller relative to the base capacitance
Solution Approach 1:
The patent extracts and removes the base capacitance component from the detection signal through a cancel circuit. The cancel circuit is configured to subtract the base capacitance value from the total measured capacitance, isolating only the variation component caused by conductor proximity. This extraction approach allows the system to maintain high base capacitance for stability while accurately detecting small capacitance variations.
Solution Approach 2:
The patent introduces a cancel circuit as an intermediary component between the detection electrode and the measurement system. This intermediary circuit processes the raw capacitance signal by removing the dominant base capacitance component, allowing the subsequent measurement system to focus on detecting only the small variation signals without being overwhelmed by the large base capacitance.
2Stability of the object's composition
If capacitance variation is small relative to base capacitance, then the detection electrode can operate with high stability, but the accuracy of detecting conductor proximity decreases
Solution Approach 1:
The cancel circuit extracts the small capacitance variation signal from the large base capacitance by performing subtraction. The circuit measures the total capacitance (base capacitance + variation) and subtracts the known base capacitance value, leaving only the variation component that indicates conductor proximity. This extraction enables accurate detection even when the variation is much smaller than the base capacitance.
Solution Approach 2:
The patent changes the measurement parameter from absolute capacitance value to capacitance variation relative to base capacitance. By transforming the measurement focus from the total capacitance (dominated by large base capacitance) to the differential variation (small but informative), the system achieves high accuracy in detecting conductor proximity while maintaining stable operation.
3Device complexity
If existing capacitance detection methods are used, then the system structure remains simple, but the detection sensitivity is insufficient for accurate capacitance measurement
Solution Approach 1:
The patent introduces a cancel circuit as an intermediary component that adds minimal complexity to the detection system. This circuit sits between the detection electrode and the measurement system, performing a simple subtraction operation to remove base capacitance. The added complexity is small compared to the significant improvement in detection sensitivity and accuracy achieved.
Solution Approach 2:
The patent replaces complex signal processing mechanisms with a simpler electrical cancellation approach. Instead of using complex algorithms or multiple sensing elements to achieve high sensitivity, the system uses an electrical cancel circuit that directly subtracts the base capacitance component, achieving high measurement precision through a relatively simple electrical mechanism.
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 approach enhances the sensitivity of capacitance detection, allowing for more accurate measurement of capacitance variations and improved touch control sensitivity, even in scenarios with high base capacitance.
Implementation Method 1
a capacitance (or referred to as a base capacitance or an initial capacitance) is formed between a detection electrode and ground. When a conductor (such as a finger) approaches or touches the detection electrode, a capacitance between the detection electrode and the ground changes.
Data Source
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AI summary
A capacitance detection circuit and a touch detection device, which are capable of improve sensitivity of capacitance detection. The capacitance detection circuit includes a front end circuit (210) and a processing circuit (220); where the front end circuit (210) comprises a first driving circuit (211), a first cancel circuit (212) and a PGA circuit (213), the first driving circuit (211), the first cancel circuit (212) and the PGA circuit (213) are connected to a first end of a detection capacitor, a second end of the detection capacitor is grounded, the first driving circuit (211) is configured to perform charging and discharging on the detection capacitor, the first cancel circuit (212) is configured to cancel a base capacitance of the detection capacitor, and the PGA circuit (213) is configured to convert a capacitance signal of the detection capacitor after the base capacitance is cancelled into a voltage signal; and the processing circuit (220) is connected to an output end of the front end circuit (210), and configured to determine a capacitance variation of a capacitance of the detection capacitor with respect to the base capacitance according to a voltage signal output by the front end circuit (210).