Capacitance Detection Circuit With Reduced Calibration Capacitor Area
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Solution Overview
Problem
Existing capacitance detecting circuits require large calibration capacitors to match the capacitance of sensing capacitors when not in use, increasing the area and cost of the circuit.
Innovation Solution
A capacitance detecting circuit with a charging and discharging module using first and second current sources, along with switches and an integrator, controls the charging and discharging of measurement and calibration capacitors to adjust their capacitance ratio, allowing for a reduced calibration capacitor value by setting the first current source's value greater than the second current source's value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitance value of the calibration capacitor is set to be approximately equal to the capacitance value of the sensing capacitor when the capacitance sensor is not operated, then the capacitance detection sensitivity is improved, but the area of the capacitance detecting circuit and chip costs are increased
Solution Approach 1:
The patent changes the capacitance value parameter of the calibration capacitor from being equal to the sensing capacitor's capacitance to being a fraction (1/N) of it. This parameter change allows the calibration capacitor to occupy less area while the current source compensation mechanism maintains the detection sensitivity by adjusting the charging current proportionally.
Solution Approach 2:
The patent introduces a current source as an intermediary element that compensates for the reduced calibration capacitor value. The current source provides proportional charging current to both the sensing capacitor and calibration capacitor, ensuring that the charge transfer relationship remains accurate even with the smaller calibration capacitor, thus maintaining detection sensitivity without requiring a large calibration capacitor.
2Measurement precision
If the capacitance value of the calibration capacitor is set to be approximately equal to the capacitance value of the sensing capacitor when the capacitance sensor is not operated, then the capacitance detection sensitivity is improved, but the chip costs are increased
Solution Approach 1:
The patent changes the capacitance value parameter of the calibration capacitor from being equal to the sensing capacitor's capacitance to being a fraction (1/N) of it. This parameter change allows the calibration capacitor to occupy less area while the current source compensation mechanism maintains the detection sensitivity by adjusting the charging current proportionally.
Solution Approach 2:
The patent introduces a current source as an intermediary element that compensates for the reduced calibration capacitor value. The current source provides proportional charging current to both the sensing capacitor and calibration capacitor, ensuring that the charge transfer relationship remains accurate even with the smaller calibration capacitor, thus maintaining detection sensitivity without requiring a large calibration capacitor.
3Measurement precision
If a calibration capacitor with capacitance value equal to the sensing capacitor is used, then the capacitance detection accuracy is maintained, but the device complexity is increased
Solution Approach 1:
The patent changes the capacitance value parameter of the calibration capacitor from being equal to the sensing capacitor's capacitance to being a fraction (1/N) of it. This parameter change allows the calibration capacitor to occupy less area while the current source compensation mechanism maintains the detection sensitivity by adjusting the charging current proportionally.
Solution Approach 2:
The patent introduces a current source as an intermediary element that compensates for the reduced calibration capacitor value. The current source provides proportional charging current to both the sensing capacitor and calibration capacitor, ensuring that the charge transfer relationship remains accurate even with the smaller calibration capacitor, thus maintaining detection sensitivity without requiring a large calibration capacitor.
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 reduces the area and cost of the capacitance detecting circuit while maintaining effective capacitance detection sensitivity by controlling the proportional relationship between the current sources.
Implementation Method 1
a first current source configured to perform charging on the measurement capacitor, and a second current source configured to perform charging on the calibration capacitor
Implementation Method 2
an integrator comprising an integrating capacitor and an amplifier, configured to convert a capacitance signal of the measurement capacitor into a voltage signal
Data Source
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AI summary
The present application discloses a capacitance detecting circuit, a touch device and terminal device, which are beneficial for reducing an area of the capacitance detecting circuit, thereby reducing costs of a chip. The capacitance detecting circuit is connected to a measurement capacitor and where it includes a calibration capacitor; a charging and discharging module including a first current source configured to perform charging or discharging on the measurement capacitor, and a second current source configured to perform charging or discharging on the calibration capacitor; an integrator, configured to convert a capacitance signal of the measurement capacitor into a voltage signal; and a control module, configured to control working states of the charging and discharging module and the integrator.