The high-speed FX correlator of Chinese VLBI network-a super spectrum analyzer based on programmable ASIC

This paper presents the principle and the structure of the 2-station "FX" VLBI correlator of the Chinese VLBI network, which is a super spectrum analyzer based on programmable ASIC. The key spectrum analysing subsystems are composed of high-speed parallel FFT pipelines, which are composed of 136 VLBAI FFT ASICs. It supports six different FFT sizes (64 to 2048 points) with the maximum data rate up to 648 Mbit/s. It takes only 16 /spl mu/s for the correlator to do 2048-point FFTs of two channels and other mathematical operations, which equates to more than 13.8 G float multiplications and 30.9 G additions every second.