Design Of IF Sampling And Digital Quadrature Demodulator In Digital Receivers

With the current improvement in key technologies such as VHIC, VLSIC etc., digital receivers are becoming a reality in Radar, EW, and wireless communication. Through digital receivers, the intermediate frequency (IF) signals or radio frequency(RF) signals from Radar are analog-to-digital converted(ADC), quadrature demodulated, and filtered, with the resulting digital data later combined via digital beamforming techniques. In such receivers, with the decrease or even abatement of some disadvantageous factors, such as temperature excursion, gain alteration, and DC voltage offset .etc, which are familiar in analog receivers, the resulting signals have much better quadurature and balance character than ones in analog receivers. The core functions of digital receivers, including forming Radar signals, are all achieved by digital technologies, which software characteristic makes receivers much flexible, opened and all-purpose.The traditional technology to design digital quadrature demodulator is based on task: the designers select ADCs and DDCs based on the design object, and choose other connection circuits. Although it is efficacious in some cases, the traditional technology also has more shortage. For examples, its self-determining interface hardware will limit its all-purpose character, and make self-exam on line to be very hard. Consequently, designers should also take care of the ability of modules to be rebuilted, examined on line, and extended, etc. Based on actual requirement, and with the improvement of FPGA,DSP, we design mutil-channels directly IF sampling and digital quadrature demodulation module based on bus-mastering, which is satisfied with the above requirement. Through the module it is able to form multiple signals in various Radar systems, which means the module is valuable and usable in various application.To achieved the design aim, many new technologies are used in the module, such as high speed and resolution ADC with big dynamic range, broad band digital demodulator integrated in FPGA, the adoption of ROCKETI/O to transfer a mass of data between boards. These technologies assure the real-time property and all-purpose character of the module, and are described in detailed in this paper.