| Phase locked demodulators are widely used for reception of amplitude modulation(AM), phase modulation(PM), and frequency modulation(FM). In this research, we concentrated on phase locked FM demodulators. Our main two parts are the PLL block and the Optimum Time Varying Filter block. We started our work by building up three basic blocks of the PLL; the PFD, the Loop Filter and the VCO. By carefully studying the structure and the operation of these blocks, we were able to make good choices regarding the types of each block and their parameters. As a result, we got the desired results in our PLL simulations. After that, in order to improve the quality of the FM signal, we worked on the Optimum Time Varying Filter which is the main research part in the overall thesis. We studied the relationship of the optimum filter (or matched filter), the optimum time-varying filter and our band pass filter. We then derived the necessary equations to realize our synchronous filter. Based on the theory and equation discussion, we were able to design the band pass filter. After we put all of the blocks together to realize our FM PLL demodulator, we simulated the whole demodulator and recovered the FM demodulated signal which showed that we had achieved our research goal-namely, to improve the quality of the PLL FM Demodulator. |
