Capacitance Sensing via DC Offset and AC Signal Injection
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Solution Overview
Problem
High-power amplifiers used in electrostatic chucking systems are bulky and lossy, and DC power supplies lack the ability to sense load capacitance, making it difficult to accurately monitor the position of workpieces during processing.
Innovation Solution
A capacitance measurement system that includes a ground connector, an output connector, a DC power source, and a time-varying signal source arranged in series, with a current monitor and capacitance module to determine capacitance based on measured current and frequency of the time-varying voltage signal, allowing for accurate capacitance sensing and workpiece positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-power amplifiers are used in electrostatic chucking systems, then the system can deliver high current, but the amplifiers become bulky and lossy
Solution Approach 1:
The patent replaces traditional high-power amplifiers with a DC power supply combined with a time-varying signal injection system. Instead of using bulky amplifiers to deliver high current directly, the system uses a compact DC power supply and superimposes AC measurement signals on top of the DC output, eliminating the need for large, lossy amplification hardware while maintaining high current delivery capability.
2Volume of moving object
If DC power supplies are used, then the form factor is small, but the ability to sense load capacitance is lost
Solution Approach 1:
The patent merges the DC power supply function with AC capacitance sensing capability by injecting a time-varying signal onto the DC power supply output. The system combines both DC voltage generation and AC measurement signals in a single integrated system, allowing the compact DC power supply to simultaneously deliver power and enable capacitance sensing through the superimposed AC component.
Solution Approach 2:
The patent introduces a time-varying signal as an intermediary carrier that enables capacitance sensing. By injecting an AC signal onto the DC output, the system creates a modulated waveform that carries capacitance information, allowing the DC power supply to indirectly sense load capacitance through the response of this intermediary signal without requiring separate sensing hardware.
3Measurement precision
If traditional capacitance sensing methods are used, then workpiece position can be monitored, but non-linearities in current measurement reduce accuracy
Solution Approach 1:
The patent transitions from direct current-based capacitance measurement to frequency-based measurement. By injecting a time-varying signal and measuring the frequency response or phase shift rather than relying on linear current measurements, the system accesses a different measurement dimension that is less susceptible to non-linearities, thereby improving both accuracy and reliability of workpiece position monitoring.
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
Enables high-resolution capacitance measurements, avoids non-linearities in current measurement, and maintains accuracy across varying capacitance ranges, improving productivity and sensitivity in electrostatic chucking systems.
Implementation Method 1
a capacitance module coupled to the current monitor, the capacitance module configured to determine the capacitance based upon the measured current
Implementation Method 2
a DC power source configured to apply a DC offset to the time-varying signal
Implementation Method 3
a current monitor configured to measure time-varying current in the conduction path
Data Source
AI summary
Systems, methods, and apparatuses for measuring capacitance of a load. An apparatus includes a ground connector, an output connector configured to couple to the load, and a time-varying signal source configured to inject a time-varying voltage signal onto a conduction path between the ground connector and the output connector. A DC power source is configured to apply a DC offset to the time-varying voltage signal, and a current monitor is configured to measure time-varying current in the conduction path. A capacitance module is configured to determine the capacitance based upon at least one of the time-varying current and a frequency of the time-varying voltage signal.