Abstract : Based on the discussion of the operating principle of the broadband RF-IF sampling down-converter, five typical modulation modes are derived in detail, and the frequency requirements for the local oscillator signal of the sampling down-converter are discussed. Through computational examples, the calculation formulas for the sampling frequency and its effective number of bits are given, and the results prove that the sampling frequency and its effective number of bits are independent of the RF bandwidth and depend only on the spectral resolution of the intermediate frequency . Keywords : down-converter, sampling frequency, RF-IF conversion [b][align=center]Research on the Character of the Sampling Frequency for Broad Band RF-IF Sampling Down-Converters LIN Mao-flu, WU Qun, WANG Hai-long, XU Hong-guang (Dept. of Electronics and Communication Engineering, Harbin Institute of Technology, Harbin 150001, China)[/ align ][/b] The formula for calculating the sampling frequency and its significant digit is presented through COB-putation examples. Computational results show that fs and its significant digit are not related to the RF bandwidth and are only determined by the resolution of the IF spectrum. Keywords : Down-converters, Sampling frequency, RF-IF conversion . Introduction The invention of s-parameter-based small-signal analysis theory and its instruments (such as vector signal generators, vector signal analyzers, vector network analyzers, etc.) and EDA development tools such as SPICE and HARMONIC BALANCE has revolutionized the radio frequency electronics industry. For decades, people have firmly believed in the s-parameter theory, considering it a universal tool for solving various RF problems. However, s-parameter theory is strictly limited to applications that satisfy the superposition theorem. This means that the input level of the RF network must be sufficiently small, which sharply contradicts the actual usage of current RF network (e.g., RF power amplifier input) levels. Therefore, since the 1980s, the nonlinear characteristics and large-signal modeling of RF microwave networks have become a research hotspot. In the research of large-signal nonlinear measurement, modeling, and application technologies for RF microwave networks, RF microwave design and simulation development tools and new testing equipment for next-generation communication systems have been developed. [b][align=center]For details, please click: Research on Sampling Frequency Characteristics of Broadband RF-IF Sampling Converters[/align][/b]