Current Measurement Circuit Disturbance Voltage Parasitic Capacitance
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Solution Overview
Problem
Capacitive sensors in lithography applications face measurement errors due to stray impedance, limited common mode rejection ratio, and parasitic capacitances introduced by long wiring connections, which complicates calibration and increases costs and complexity.
Innovation Solution
A current measuring circuit with a voltage source generating a disturbance voltage, connected to the power supply terminals, is used to subtract voltage errors and minimize parasitic capacitances by driving both the sensor wire and shield conductor with the same voltage, reducing measurement errors and eliminating the need for extensive calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If measurement circuits are located remotely from capacitive sensors, then access for maintenance is improved and heat removal is facilitated, but parasitic capacitances are introduced into the system which affect sensor readings
Solution Approach 1:
The measurement circuit is extracted from the sensor location and placed remotely, separating the sensing function from the measurement function. This allows maintenance access while managing parasitic effects through dedicated compensation circuitry located at the remote measurement station.
Solution Approach 2:
A compensation circuit acts as an intermediary between the sensor and measurement system, generating compensating signals that counteract the effects of parasitic capacitances introduced by long wiring connections.
2Length of stationary object
If the length of wiring connection between sensor and measurement circuit is increased, then remote measurement is achieved, but measurement errors increase due to parasitic capacitances
Solution Approach 1:
The compensation circuit serves as an intermediary that actively counteracts the harmful effects of long wiring connections by generating compensating signals that cancel out parasitic capacitance effects, enabling accurate measurement despite extended wiring lengths.
Solution Approach 2:
The system changes the electrical parameters (voltage signals) applied to the wiring to compensate for parasitic effects, using variable compensation signals that adapt to different wiring configurations and lengths.
3Measurement precision
If calibration of sensor and wiring combination is performed, then measurement accuracy is improved, but system flexibility is reduced and cost increases
Solution Approach 1:
The compensation circuit performs automatic self-calibration by continuously monitoring and adjusting compensating signals based on real-time measurements, eliminating the need for manual calibration procedures and reducing system complexity.
Solution Approach 2:
The system implements feedback mechanisms where measurement results are continuously monitored and used to adjust compensation parameters automatically, maintaining accuracy without requiring external calibration interventions.
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 significantly reduces measurement errors, eliminates the need for complex calibration, and enhances the sensitivity and accuracy of capacitive sensor measurements, particularly in challenging environments like vacuum systems, by isolating the sensor current from parasitic capacitances.
Implementation Method 1
a first voltage source coupled to the one or more power supply terminals, the first voltage source providing a disturbance voltage to the one or more power supply terminals, the disturbance voltage representing a voltage at the first input terminal
Data Source
AI summary
A measurement system for measuring an input electrical current (Ics) from a current source (CS) and generating a current measurement signal, comprising a current measuring circuit (70) having a first input terminal (72) connected to the current source and an output terminal (74) for providing the current measurement signal. The current measuring circuit further comprises one or more power supply terminals (75, 76) arranged to receive one or more voltages from a power supply (77a, 77b) for powering the current measuring circuit. The current measuring circuit also comprises a first voltage source (VD) coupled to the one or more power supply terminals, the first voltage source providing a disturbance voltage to the one or more power supply terminals, the disturbance voltage representing a voltage at the first input terminal.