| This thesis discusses the key techniques of digital direct sequence spread spectrum and de-spread spectrum communication base band circuit & intermediate frequency circuit. The base band circuit includes digit multiple & de-multiple based on DS2154, digital down converter, digital PN code matched filter and carrier recovery of digital demodulation based on STEL-2000A, and high speed ADC. The intermediate frequency circuit includes QPSK modulation based on HFA3724, PLL circuit based on MB1502. All system controlled by AT89C52 and M4A5 128/64 CPLD.This digital direct sequence spread spectrum system's data rate is 2.048Mbps, the length of PN code is 11, the IF frequency is 70MHz. |
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