Digital RF Amplitude Control for Mass Spectrometer Quadrupoles
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Solution Overview
Problem
Analog feedback circuitry in mass spectrometers is costly and has a slow response time, leading to inaccuracies in adjusting the amplitude of radio frequency (RF) signals, which affects the performance of the instrument.
Innovation Solution
A digital control system using an analog-to-digital converter (ADC) and a controller circuit that applies digital signal processing (DSP) techniques, such as discrete cosine transform (DCT), to accurately adjust the amplitude of RF signals by identifying fundamental frequencies and harmonics, thereby improving the precision and speed of signal adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If analog feedback circuitry is used to adjust RF signal amplitude, then the system can maintain continuous amplitude control, but the response time is slow and component costs increase
Solution Approach 1:
The patent replaces the analog feedback circuitry (electrical/mechanical system) with a digital control system that samples the RF signal, processes it through digital signal processing, and adjusts the amplifier gain digitally. This substitution eliminates the slow analog feedback loop while maintaining amplitude control accuracy through digital processing of the sampled signal and harmonics.
Solution Approach 2:
The patent uses an analog-to-digital converter to create a digital copy of the RF signal, which then undergoes digital signal processing to extract amplitude and frequency information. This digital copy allows for rapid processing and analysis without affecting the original RF signal, enabling fast response time while maintaining measurement accuracy.
2Reliability
If analog feedback circuitry with multiple components is used, then amplitude control is achievable, but system cost and complexity increase
Solution Approach 1:
The patent replaces multiple analog circuit components with a streamlined digital control system consisting of an analog-to-digital converter, digital signal processing unit, and digital amplifier control. This substitution reduces component count and system complexity while maintaining or improving amplitude control capability through software-based processing algorithms.
Solution Approach 2:
The digital control system performs multiple functions using a unified architecture: it samples the RF signal, extracts fundamental frequency amplitude, identifies harmonic content, determines frequency deviation, and adjusts amplifier gain all through a single integrated digital processing pathway, eliminating the need for separate analog circuits for each function.
3Measurement precision
If digital signal processing is used to analyze RF signal, then measurement precision and adjustment speed improve, but processing complexity increases
Solution Approach 1:
The patent segments the digital signal processing into distinct functional stages: sampling the RF signal, extracting the fundamental frequency component, identifying harmonic content, calculating frequency deviation, and generating correction signals. This segmentation allows each processing step to be optimized independently and simplifies the overall complexity by breaking down the processing into manageable, sequential operations.
Solution Approach 2:
The patent introduces intermediate calculations and representations during digital signal processing, such as computing the ratio of fundamental frequency amplitude to total signal amplitude, and using harmonic content as an intermediary metric to determine frequency deviation. These intermediaries simplify the final amplitude measurement and control decisions while maintaining high precision.
Data Source
AI summary
Control of an amplitude of a signal applied to rods of a quadrupole is described. In one aspect, a mass spectrometer includes an amplifier circuit that causes a radio frequency (RF) signal to be applied to the rods of the quadrupole based on an amplifier RF input signal. An analog-to-digital converter (ADC) can generate a digital representation of the RF signal. A controller circuit can receive the digital representation and adjust an amplitude of the amplifier RF input signal based on differences between an amplitude of a fundamental frequency of the RF signal being different than an expected amplitude.