HIGH-SPEED DIGITIZER AVERAGER DATA-ACQUISITION SYSTEM FOR FOURIER-TRANSFORM ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY/

A high-speed digitizer/averager data-acquisition system designed and b uilt as part of a 300-MHz Fourier transform electron paramagnetic reso nance spectrometer is described. There are two key features of the sys tem: (1) the maximum digitizing rate is 300 Msamples/s and (2) a 256-p oint free-induction-decay signal running summation can be updated in l ess than 3 mu s. At the maximum digitizing rate, the system can sum 65 536 FIDs in 220 ms. The system consists of an analog-to-digitar conve rter/adder unit (ADCA) and an IBM compatible personal computer. The AD CA is comprised of a digitizer, high-speed sample buffers, high-speed adders/memory, and control hardware. Design techniques, such as parall el processing, utilized to meet the high-speed performance requirement s are described. Trigger and timing signals for the system are derived from the spectrometer. System efficiency, synchronization, and time b ase stability are demonstrated in the spectrometer at a sampling frequ ency of 200 MHz. Signal-to-noise ratio enhancements are shown using a lithium phthalocyanine test sample.