| Magnetic resonance imaging(MRI)is based on nuclear magnetic resonance technology and is an important instrument for modern medical examination.The diagnosis and screening of diseases by MRI can reduce the sufferings of patients,increase the convenience and safety of diagnosis,as well as save time and cost.Magnetic resonance imaging(MRI)is of great significance for improving the national medical standard and improving people's livelihood.At the same time,MRI is a comprehensive product of multidisciplinary and multi technology.Its design is complex,and its technical requirements are high.It also marks the scientific research level of a country.However,most of the existing MRI are monopolized by foreign manufacturers,which are expensive and costly to maintain.With the improvement of people's living standards,the demand for magnetic resonance imaging equipment is becoming more and more important.It is of great strategic significance to develop a magnetic resonance imaging instrument with independent intellectual property right for the development of the country.This paper,based on the magnetic resonance imaging instrument,develops the 1KW RF power amplifier suitable for magnetic resonance imaging system,introduces the related performance indexes and basic principles of the RF power amplifier,compares and selects the circuit configuration,work category and common structure of the power amplifier,and briefly explains the RF power amplification.According to the requirements of MRI,the design index and overall scheme of the power amplifier developed in this subject are worked out.Based on these indicators,by analyzing the characteristics of different types of power amplifiers,LDMOS is chosen as the amplifier of the last stage 1KW power amplifier.In view of the selected transistors,the principle and the realization process of each design link are discussed in detail,including the design of the bias circuit,the design of the matching network,the design of the stable circuit and so on.The most crucial matching network is accomplished by broadband matching,and the impedance transformer is transformed by transmission line transformer.Due to the special structure of components and the characteristics of high voltage and high current of power amplifier,special design of PCB has been made,and heat sink has been added.In order to facilitate the control of the imager,ensure the safety and good performance of the power amplifier,the switch control circuit,the protection circuit and the low pass filter are designed.Finally,after testing,it is verified that the power amplifier can work normally and meet the design requirements. |
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