Abstract : Digital down-conversion is one of the core technologies of software-defined radio. STRATIX EPIS25 is a powerful FPGA from ALTERA. This paper elucidates the principle of digital down-conversion, presents an implementation method based on this chip, and experimental results demonstrate the effectiveness of the method. This may avoid the use of dedicated hardware down-converters, simplifying the hardware circuit and increasing system flexibility. Keywords: Software-defined radio, digital down-conversion, FPGA, DspBuilder, SignalTap 1 Introduction In modern electronic technology, software-defined radio (SDR) is widely used. The concept of SDR was first clearly proposed by Joe Mitola at the US Telecommunication Systems Conference in May 1992, and has since attracted widespread attention and research. The idea of ​​SDR is to place broadband A/D and D/A converters as close to the antenna as possible, construct a general-purpose hardware platform, and implement various functions, such as operating frequency bands, modulation and demodulation, and communication protocols, in software. SDR emphasizes the openness and full programmability of the architecture, changing the hardware configuration structure through software updates to achieve new functions. The main characteristics of SDR are: a. Flexibility. Software-defined radio (SDR) can easily add new functions by adding software modules. b. Openness. Due to its modular and standardized structure, the hardware of SDR can be updated or expanded as devices and technologies develop, and the software can be continuously upgraded as needed. Because of its flexibility and openness, SDR has freed communication systems from application-oriented design thinking, and is considered another breakthrough in wireless communication after the transition from analog to digital and from fixed to mobile. The block diagram of an ideal SDR system is shown in Figure 1. [align=center] Figure 1 SDR Block Diagram [/align] [b][align=center]For more details, please click: A Digital Down-Converter Based on STRATIXEP1S25[/align][/b]