Ion Pump Power Supply Noise Cancellation Circuit
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Solution Overview
Problem
Ion pumps in charged particle beam apparatuses face challenges in maintaining ultrahigh vacuum states due to low frequency noise interference, which hinders accurate load current detection and vacuum measurement in electron microscope systems.
Innovation Solution
Incorporating a canceller circuit within the load current detection circuit of the ion pump power supply, with equal impedances to the main circuit and high voltage cable, to reduce low frequency noise, including components like capacitance equal to cable capacitance, current voltage conversion circuits, and inverting amplifiers, to cancel noise effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high voltage cable is used to connect the ion pump and power supply, then the ion pump can be operated, but low frequency noise is superimposed on the load current detection circuit via cable capacitance, preventing 1 nA order detection accuracy
Solution Approach 1:
The patent converts the harmful low frequency noise superimposed on the detection circuit into a useful signal by generating a cancellation signal that mirrors the noise characteristics. The noise, which was previously an obstacle to 1 nA order detection accuracy, is now systematically counteracted through the cancellation circuit, allowing the detection system to achieve the required precision while maintaining reliable vacuum operation.
Solution Approach 2:
The patent introduces a cancellation circuit as an intermediary element between the high voltage cable and the load current detection circuit. This intermediary generates and injects a cancellation signal that neutralizes the noise coupled through the cable capacitance, enabling the detection circuit to achieve 1 nA order accuracy without removing the cable or changing the ion pump operation.
2Productivity
If low frequency noise is present in the high voltage circuit output, then the ion pump operates, but the noise cannot be filtered without affecting the ion pump operation or vacuum measurement accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the cancellation circuit continuously monitors the noise characteristics in the high voltage circuit output and dynamically adjusts the cancellation signal to match and neutralize the noise. This feedback loop ensures that the ion pump operates normally with the full high voltage signal while the detection circuit receives a noise-free version, achieving both productive operation and precise measurement.
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 configuration allows for precise measurement of load currents down to 1 nA order, ensuring the electron gun's environment is in an ultrahigh vacuum state, enhancing the accuracy of electron microscope measurements.
Implementation Method 1
by applying a high voltage between an anode and a cathode in an evacuation mechanism and applying a strong magnetic field from the outside, electrons generated from the cathode collide with gas molecules and the gas molecules are ionized
Implementation Method 2
the leakage parabolic voltage leaked from a parabolic voltage generation circuit to an operational amplifier of a pulse width control circuit via a high voltage resistance circuit is cancelled by adding a divider parabolic voltage of the same amplitude and the same phase as the leakage parabolic voltage to the operational amplifier and performing differential amplification
Data Source
AI summary
In a charged particle apparatus with an ion pump, which is a charged particle beam apparatus with an ion pump including a charged particle beam irradiation detecting unit for irradiating a sample with a charged particle beam in a chamber and detecting a secondary charged particle, an image processing unit for forming a secondary charged particle image from a detection signal of the detected secondary charged particle, an output unit for processing at the image processing unit and outputting an image, an ion pump for maintaining the interior of the processing chamber in a vacuum state, a driving power supply unit of the ion pump, and a high voltage cable for connecting the ion pump and the driving power supply unit, the driving power supply unit of the ion pump is structured to include a high voltage power supply circuit unit for operating the ion pump, a load current detection circuit unit for detecting a load current applied to the ion pump, and a canceller circuit unit for reducing low frequency noise applied to the load current detection circuit unit in order to sufficiently reduce low frequency noise of the power supply of the ion and to measure the degree of vacuum with a high accuracy.