Design and Implementation of a Digital Backend Incorporating a Zoom-PFB Algorithm Based on a ROACH System

In this paper we describe design and implementation of a digital backend system for a radio-telescope receiver based on a ROACH system and a Xilinx System Generator.The system incorporates a Zoom-PFB algorithm.We first discuss principles of a Zoom-PFB algorithm and approaches to use an FPGA to realize the key parts of a Zoom-PFB, the low-bandpass filtering and decimation.To meet the demand of high-resolution observation of parts of spectra around a spectral line, we have designed the backend system by dividing its 400MHz bandwidth into 16 bands, each of which extends 25MHz and is further divided into 6k channels with a frequency resolution of about 4kHz.We have analyzed the specifications of the system and have carried out tests for its performance under laboratory conditions.We have also verified the feasibility of our design by using the system to observe the 21cm hydrogen line from the Galactic plane.The observation is through a radio telescope of a 4.5m antenna of the X/Y structure.