The Research On RF Power Amplifier And Its Linearization Or Mid/low-field MRI

Nuclear magnetic resonance imaging (NMRI) is one of the important directions ofmodern medical image technology. As the aging of the Chinese population accelerating,development of imaging system with stable in performance and competitive in price is one ofthe most important missions of medical equipment companies in our country. Radio frequencypower amplifier (RFPA) is an important part of NMRI system, to amplify signal in specialnarrow-band frequency. The amplified signal will then be transfer to, and delivered by bodycoil, which will generate a RF field around space under body coil. Our country is week inNMRI technology, especially on RFPA, so this research is meaningful.This thesis does preliminary research on RFPA for middle-low filed NMRI system,designing20MHz power amplifier which include power supply, bias, timing, match, andfeedback, in a low cost way.This design gets a innovation on power combination. Through synthesis of parallelstructure, push-pull structure and inductive coupling, a complex-power combine structure isdesigned and realized in way of microstrip. A comprehensive evaluation way of modeling,computation of S parameter, and characteristic is used to analyze the transmission of thestructure. Under test, eight MOSFET is combined with this structure, and get2000W poweroutput under pulse work mode, with a loss of less than0.2dB.This thesis studies Cartesian’s feedback loop in narrowband using, combines it withRFPA and do experiment. Result show an improvement on stability of gain, less than±0.9dB to less than±0.15dB, and three inter-modulation index is increased by12dBc.