Development of a high-speed digital signal process system for bunch-by-bunch feedback systems

Abstract

High-speed digital filter systems for bunch-by-bunch feedback systems have been developed at KEK. A two-tap finite impulse response filter with simple hardware realizes the functions of a 90° phase shift, suppression of the static component and digital delay of up to a few hundred turns for the KEKB rings. Difficulties in the circuit board, such as the trimming of the timing skews or the problem of long-term reliability, have been solved using custom GaAs large-scale integrated circuits which demultiplex and multiplex fast parallel-digital data coming from the analog-to-digital converter and going to the digital-to-analog converter. Two major applications of the filter board, the bunch current monitor and the bunch oscillation recorder with 20 MB memories for transient-domain analysis of the instabilities, are also described.