Design and prototype of an all digital system for baseband FM multiplex signal demodulation

Abstract

The continuing increase in transistor densities and operation frequencies of digital circuits is leading to the replacement of many analog circuits by their digital circuit counterparts. This trend can be attributed to the flexibility and robustness provided by digital circuits over analog circuits. One application in which digital circuits are replacing analog circuits is in the modulation and demodulation of baseband frequency modulated (FM) radio signals. In this project, an all digital system for demodulating baseband FM Multiplex (MPX) signals is simulated, designed, and prototyped on a Xilinx Spartan-3AN FPGA. The design architecture is simulated using Scilab numerical computation software; implemented in Verilog Hardware Description Language; and tested using the digital to analog converters (DACs) on the Xilinx Spartan-3AN Starter Kit. The oscilloscope images at the end of this report show that the implemented system can successfully demodulate the 19kHz pilot tone, left channel signal, and right channel signal of a digitized FM MPX modulated signal sampled at 192kHz.