Capacitive Sensor Read-Out Circuit With Adaptive Duty Control
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Solution Overview
Problem
Capacitive sensors face challenges in accurately reading signals due to noise introduced when one terminal of the capacitor is grounded, making it difficult to identify precise capacitance changes.
Innovation Solution
A read-out circuit is designed with an operational amplifier, feedback capacitor, sensor charging and discharging circuit, switching circuits, and a duty control circuit that adjusts the duty ratio based on sensor capacitance, allowing for accurate signal reading by minimizing noise through controlled charging and discharging operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one terminal of the capacitor is grounded in the capacitive sensor, then the circuit structure is simplified, but noise is introduced through the grounded node making it difficult to identify accurate signals
Solution Approach 1:
The patent extracts the grounded node from the sensing circuit by using a floating capacitor configuration where neither terminal is directly grounded during the sensing phase. The capacitor is charged through a charge pump circuit that isolates it from ground, thereby removing the noise source while maintaining circuit functionality.
Solution Approach 2:
The patent introduces a charge pump circuit as an intermediary between the capacitor and ground. This charge pump serves as a mediator that transfers charge without creating a direct ground connection, thereby eliminating noise while still allowing the capacitor to function properly in the sensing circuit.
2Measurement precision
If the sensor is charged or discharged for a longer time, then the output voltage convergence is ensured and measurement accuracy is improved, but the reading speed and productivity are reduced
Solution Approach 1:
The patent employs periodic charging and discharging cycles with optimized duty ratios. By using alternating phases of charging, discharging, and sensing with specific time allocations, the system achieves voltage convergence within each cycle while maintaining high reading throughput through the periodic nature of the operation.
Solution Approach 2:
The patent dynamically adjusts the charging and discharging time constants based on the sensor capacitance value. The duty control circuit modifies the timing parameters in real-time to match the specific sensor characteristics, ensuring optimal convergence speed for each sensor while maximizing reading throughput.
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 solution effectively reduces noise and ensures accurate measurement of capacitance changes by ensuring sufficient time for output voltage convergence, enhancing the reliability of capacitive sensor readings.
Implementation Method 1
In a capacitive sensor that senses a signal in a manner in which capacitance of a capacitor is changed, a read-out circuit includes a circuit that converts a change in capacitance into a voltage
Implementation Method 2
a feedback capacitor connected between an output terminal of the operational amplifier and a negative input terminal of the operational amplifier
Data Source
AI summary
A read-out circuit includes an operational amplifier configured to receive an input voltage through a positive input terminal; a feedback capacitor connected between an output terminal of the operational amplifier and a negative input terminal of the operational amplifier; a sensor charging and discharging circuit configured to charge or discharge a sensor during a first time; a switching circuit connecting the sensor and the operational amplifier during a second time after the sensor is charged or discharged; and a duty control circuit configured to determine a duty ratio of the first time and the second time according to a capacitance of the sensor.