A precision frequency synthesizer with direct digital synthesis for a low-field magnetic-resonance imager

Abstract

A frequency synthesizer of the microwave spectrometer of a magnetic-resonance imager (MRI) with a 0.06-T intensity of the basic magnetic field is described. The synthesizer is based on a programmable logic integrated circuit and a direct digital synthesis microcircuit. The synthesizer is capable of operating in a range up to 70 MHz with a 3-μHz tuning step, allowing one to use it in MRI systems with a basic magnetic intensity of up to 1.5 T. The unit is intended to store up to 16348 frequency values in its random-access memory, and the switching is carried out by a logic signal, the source of which can be, e.g., a pulse train programmer of the microwave spectrometer. The frequency switching rate is 1 kHz and higher. The synthesizer is loaded through a USB 2.0 standard interface.