FM radio receiver with digital modulation using VLSI

ABSTRACT

This VLSI project shows the design, building and testing of an FM receiver. This system is divided into two parts the analogue FM modulator and digital demodulator. The main part of this work is to convert the RF signal into a frequency lower than the sample to a digital converter. The second part works as a phase loop method of demodulating FM signal.

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INTRODUCTION

The past radio receivers are made with analogue circuits and faced all the problems of the circuit. Initial digital circuits and computers are not used for the high-frequency circuits. Today digital receivers are designed with high technology which can be used in high frequencies such as software designed radio. The two parts of the system work accordingly to be more efficient.

A digital FM demodulator design can be done in software or hardware. Software is quicker to implement because you can write in high-level languages such as C. The hardware description languages used in VHDL. And in this project, we use different types of boards such as NEXYS.

In this FM demodulator technique we used to draw the phase-locked loop (PLL). This project is divided into two sections they are

1. FM demodulator design
2. FM radio front end

To control this FM radio front end we use a gain controller.

And same as it is in demodulator the section will be divided into two parts they are

1. Testing of the demodulator
2. Testing of the front end

Finally, the component was integrated together as a75Ohm impedance FM antenna was plugged into the Antenna input of the system. The receiver is a 50Ohm system so there is a slight mismatch which may account for some signal attenuation of the RF signal. An audio amplifier was connected to the audio output, and then to a speaker. Initially, only faint whispers of music made it through the system, although it was mostly noise. However, after I discovered a bad amplifier and replaced it I was able to pick up the following stations at my house: 88.5, 89.3, and 91.3MHz.

 Using the large rooftop antenna on campus I was able to pick up many more stations although they were all noisier than the three stations I picked up with the small dipole antenna.

CONCLUSION

This FM receiver was a successful method as we can see it is used in FM radio stations. And for better receiving, we can use receivers with additional gain at the RF stage and by using balancing mixers etc. This FM receiver is expensive, large and noisy but we can use this for experiencing RF design and also implement the phase loop method.

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FM radio receiver with digital modulation using VLSI