An improved wideband digital baseband conversion method

The mismatching of high ADC sampling frequency with low FPGA operating speed restricts the application of conventional baseband converter in wideband receiver. The efficient baseband conversion method based on Polyphase Filter Bank (PFB) & Discrete Fourier Transform (DFT) can decrease the sampling frequency greatly, whereas, this method has processing dead zone and is not flexible. A new approach based on conventional baseband conversion method is presented in this article. The key feature of this approach is the combination of parallel mixing structure with the polyphase decomposition of Low Pass Filter (LPF). Due to the parallel processing structure and the freedom in choosing intermediate frequency to be down-converted, the new approach is particularly suited for the general wideband baseband converter. The analytical derivation of the new method is detailed. A design scheme with 1024MHz sampling frequency is proposed. Moreover the proposed scheme is implemented on an FPGA evaluation board, and validity of the system is confirmed on a real hardware.