A design is presented to solve the problems of huge resource and time consuming

low computation efficiency and unsuitable for variable bandwidth signals

which are the bottleneck of digital down conversion（DDC）

that provides a polyphase architecture of bandpass filter based on the research of the computation of the generalized DDC and polyphase architecture.Some approaches are presented

including multipliers with fixed working frequency

multipliers reusing

multirate input and output control etc

which provide the proposed architecture the capacity of DDC for signals with different bandwidth.At the same time

its computation efficiency is enhanced and the amount of multipliers and time for dealing with signal can also be reduced.Its perfect properties are verified by the results of software and hardware simulation.