Digital Fm Receiver_kar

DIGITAL FM RECEIVER

S.KARTHIK D.E.E.E.,D.I.S.,B.E.

Aim Of the Project  To develop a Digital FM receiver using

VHDL.  To optimize the design of PLL and NCOs.  To minimize the gate count and area.

Introduction  FM signals can be demodulated using

various techniques such as, Differentiator and Envelope Detector, Zero Crossing Detector, Phase Lock Loop (PLL).

 The design of the Digital FM Receiver

circuit in this project uses Phase Locked Loop (PLL) as the main core.

PLL  PLL demodulators are widely used in

today’s communication systems because of their superior performance, ease of alignment, and ease of implementation using inexpensive integrated circuits.

 If PLL is locked to a FM signal, the

VCO tracks the instantaneous frequency of the input signal.

Working Principle  Frequency

modulated input signal is assumed as a series of numerical values (digital signal) via 8-bit of analog to digital conversion (ADC) circuit.

 The FM Receiver gets the 8 bit signal every

clock cycle and outputs the demodulated signal.

Architecture Description  The system of Digital FM Receiver consists of a

digital PLL cascaded with digital low pass filter.  The important blocks in the Digital FM receiver are, Phase detector. A Low pass filter. An Error amplifier. A VCO/ NCO.

Block Diagram

Phase Detector  Phase detector compares the phase and

frequency of the incoming signal to that of the output of the VCO/NCO.  If the two signals differ in frequency an error voltage is generated.  It is basically a multiplier.

Loop Filter  Loop filter will remove the high frequency

component.  The difference frequency component is amplified and then applied as control voltage to the VCO.

VCO  A voltage-controlled oscillator or VCO is

an electronic oscillator designed to be controlled in oscillation frequency by a voltage input.  It is a free running oscillator and operates at a set of frequency.  It can be shifted to either side by applying a DC control voltage.

NCO  A numerically controlled oscillator (NCO) or

digitally controlled oscillator (DCO) is an electronic system for synthesizing a range of frequencies.  DCOs have been used as cheap replacements for VCOs.  Numerical Controlled Oscillator (NCO) will take the

corrective error voltage, and then shift its output frequency from its free-running value to the input signal frequency and thus keep the PLL in lock.

Merits  NCOs are phase continuous and are better

than VCOs.  Since the NCO is highly linear, it is possible to realize high linear FM demodulators.

Applications  With the advanced technology,

FM detectors using PLL are widely used in various FM communication systems.

Design Flow

HDL to be used

VHDL-93(IEEE Std. 1076-1993) or VERILOG(IEEE Std. 1364).

FPGA to be used

 ALTERA CYCLONE II. (or)  XILINX SPARTAN II XC2S200.

Works done

 Collected related materials.  Attended ALTERA demo.

Future works  Algorithmic Survey.  To optimized the multiplication operation

used in the phase detector component.  Develop HDL coding.  Functional simulation and logic verification.  Synthesis.  Implementation on FPGA.  Backend if possible.

References

 Michel.

C. JeruchimSimulation Of Communication Systems Modeling, Methodology and Techniques.  Simon Haykin – Communication Systems.  D. Roy Choudhury – Linear Integrated Circuits.

Suggestions, if any?

Thank u for Ur suggestions