DDC is the key technique of acquiring baseband signal in the digital radar receiver. The data calculated by digital down conversion (DDC) need to be truncated in the fixed-point platform such as field programmable gate array (FPGA). However, the error of inappropriate truncation may result in the zero-drift in the output signal and leads to the degradation of dynamic range of radar receiver. In this paper, the zero-drift caused by direct LSBs truncation is analyzed, and the tending truncation method and the round-up truncation method are proposed. Both of these methods can make the truncation error approach to zero and restrain the zero-drift effectively.
