Design and Realization of Time-domain Transfer DPD Method for MRI RF Power Amplifiers

This paper presents a novel digital pre-distortion (DPD) method for magnetic resonance imaging radio frequency power amplifiers (MRI RFPAs) using a time-domain transform model (TDTM) for feedback and feedforward. The TDTM is derived using a memory polynomial DPD method for MRI RFPA operations. The proposed DPD includes two pre-distorters placed on the front of the main and auxiliary power amplifiers, respectively. The MRI RF signal is input to splitter power amplifier modules before being combined to output a linear high-power signal. An analog-digital converter (ADC) collects the final combined output power with a directional coupler to measure the coefficient of the proposed DPD algorithm. The DPD coefficient is updated in real-time as the linearity becomes worse during the RFPA process to ensure that the RFPA maintains good linearity. A 3.0-T MRI RFPA is realized using the proposed DPD architecture with a main power of 1 kW at 12S MHz. A 100-W auxiliary power amplifier is used to obtain a linear power amplifier of about 1 kW. The established test bench verifies the DPD RFPA performance at 128 MHz (3.0-T resonator frequency), achieving good linearity with high efficiency, exhibiting gain variations of no more than 0.2 dB and phase variations of no more than 1°. The efficiency is approximately 60%. Finally, the RFPA with this DPD method is integrated into a 3.0-T MRI system, and good-quality imaging is achieved.