High-speed digitizer/averager data-acquisition system for fourier transform electron paramagnetic resonance spectroscopy

Abstract

A high-speed digitizer/averager data-acquisition system designed and built as part of a 300-MHz Fourier transform electron paramagnetic resonance spectrometer is described. There are two key features of the system: (1) the maximum digitizing rate is 300 Msamples/s and (2) a 256-point free-induction-decay signal running summation can be updated in less than 3 μ s. At the maximum digitizing rate, the system can sum 65 536 FIDs in 220 ms. The system consists of an analog-to-digital converter/adder unit (ADCA) and an IBM compatible personal computer. The ADCA is comprised of a digitizer, high-speed sample buffers, high-speed adders/memory, and control hardware. Design techniques, such as parallel processing, utilized to meet the high-speed performance requirements are described. Trigger and timing signals for the system are derived from the spectrometer. System efficiency, synchronization, and time base stability are demonstrated in the spectrometer at a sampling frequency of 200 MHz. Signa-to-noise ratio enhancements are shown using a lithium phthalocyanine test sample.