FPGA-based digital direct-conversion transceiver for Nuclear Magnetic Resonance Systems

Direct-conversion is an alternative to the established superheterodyne architecture for Nuclear Magnetic Resonance (NMR) transceivers. In this work, a digital direct-conversion transceiver for NMR is described. Following a software-defined radio paradigm, all signal processing tasks - including down-conversion to baseband - are performed in the digital domain, without analog heterodyning at the transceiver front-end. A programmable NMR pulse programmer with a minimum resolution of 24 ns is also integrated in the transceiver design, which allows the execution of user-defined pulse sequences. The RF Transceiver architecture is implemented in an Altera Cyclone II FPGA, and described in the VHDL hardware description language. The proposed architecture is suited for compact, low-cost NMR systems, for education and research, and is capable to perform experiments in areas such as NMR spectroscopy and relaxometry.