Capacitance Sensing Circuit for Short/Open State Detection
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Solution Overview
Problem
Existing capacitance detection devices face challenges in accurately determining short-circuit and open states due to parasitic capacitance errors, which complicates the structure and increases the number of components required for error correction.
Innovation Solution
A capacitance detection device with a first capacitor between a detection electrode and a node, a second capacitor between the node and ground, and a third capacitor between the node and a shield electrode, utilizing an alternating-current voltage output circuit, attenuation circuits, and a charge amplifier to differentiate between short-circuit and open states based on changes in alternating-current voltage amplitude and phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shield electrode is placed around the detection electrode to reduce parasitic capacitance error, then measurement precision is improved, but device complexity increases due to additional components and circuits required for state determination
Solution Approach 1:
The detection signal processing circuit is designed to perform multiple functions: it determines both the short-circuit state and open state using the same signal processing pathway. The circuit analyzes the detection signal to identify state information without requiring separate dedicated circuits for each state determination, thereby reducing overall device complexity while maintaining measurement precision through the shield electrode configuration
Solution Approach 2:
The circuit uses feedback mechanisms to analyze the detection signal and determine system states. By continuously monitoring the detection signal characteristics and comparing them against expected patterns for different states (short-circuit, open, normal operation), the circuit can accurately identify system conditions without adding complex external monitoring equipment
2Reliability
If special circuits are added to determine short-circuit and open states, then reliability is improved, but device complexity increases due to increased number of parts
Solution Approach 1:
The existing detection signal processing circuit is designed to serve multiple purposes: it processes the capacitance detection signal and simultaneously determines both short-circuit and open states. This multi-functional approach ensures reliable state determination without requiring separate dedicated circuits for each function, thereby maintaining reliability while avoiding the increase in component count that would result from adding special-purpose circuits
Solution Approach 2:
The detection signal processing circuit performs self-diagnosis by analyzing its own detection signals to determine system states. The circuit uses the detection signal characteristics to identify whether the system is in a normal state, short-circuit state, or open state, without requiring external monitoring systems or additional diagnostic components. This self-service capability ensures reliable state determination while minimizing additional hardware
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 allows for the simple determination of short-circuit and open states with enhanced detection sensitivity and reduced noise interference, improving the accuracy of capacitance detection.
Implementation Method 1
a first capacitor C1 disposed in a path between a first node N1 connected to the detection electrode Es and a second node N2; a second capacitor C2 disposed in a path between the first node N1 and ground; a third capacitor C3 disposed in a path between the first node N1 and a third node N3 connected to the shield electrode Ea
Implementation Method 2
an alternating-current voltage output circuit 31 that outputs a first alternating-current voltage Vas to the third node N3
Implementation Method 3
a charge amplifier 33 that supplies charge to the first capacitor C1 through the second node N2 and outputs a detection signal Vo matching the supplied charge
Data Source
AI summary
A capacitance detection device has: a first capacitor disposed in the path between a first node connected to a detection electrode and a second node; a second capacitor disposed in the path between the first node and the ground; a third capacitor disposed in the path between the first node and a third node connected to a shield electrode placed in proximity to the detection electrode; an alternating-current voltage output circuit that outputs a first alternating-current voltage to the third node; a first attenuation circuit that outputs a second alternating-current voltage resulting from attenuating the amplitude of the first alternating-current voltage; and a charge amplifier that supplies charge to the first capacitor through the second node and outputs a detection signal matching the supplied charge.