Direct Digital Frequency

Synthesizer(DDFS)A Project Submitted by

S. R. Karthik (13110106051)

A .Venkatachalam (13110106108)

N. Vignesh (13110106111)

Final year, Department of Electronics & Communication,

R.M.K College of Engineering & Technology

UNDER THE GUIDANCE OF

Dr.N.Gangatharan

HOD,Dept. of ECE,RMKCET.

Abstract

• Direct Digital Synthesis (DDS) is an electronic

method for digitally creating arbitrary waveforms

from a single, fixed source frequency.

• Direct Digital Frequency Synthesis (DDFS) is a

mixed signal part i.e. it has both digital and

analog parts.

• DDFS’s digital part is also known as Numerically

Controlled Oscillator (NCO).

Objective

• To understand and analyze the working of a DDFS

system .

• To create an LUT(look-up-table) for Numerically

controlled oscillator(NCO) to aid the optimized

wave generation.

Overview of the project

• Introduction

• Literature Survey

• Existing system

• Proposed System

• Frequency tuning equations

• Numerically Controlled Oscillator(NCO)

• Specification of NCO

• Tools and system Requirement

• Coding and Algorithm

• Testing

• RTL Schematic

• Waveform and simulation

• Application

• Conclusion

• Future work

• References

Introduction• This system was proposed by J.Tierney in the year

of 1971.

• The output wave form utilizes sampling theory to synthesize.

• It consists of NCO as Digital Part ,DAC and RLPF forms the analog part .Frequency control register NCO

Reference oscillator

DAC Reconstructio

n LPF

N M

fclk Analog output

Literature SurveyTitle of the Paper

Author

Inference & Drawback

Year of Publication

A portable Digitally Controlled Oscillator(DCO) using noval varactors

Pao-Lun Cheng,Chen-Yi Lee

Implemented the whole problem statement using the Gate- flow logic model and there is no scope for application on a large scale basis

May 2011

An Ultra low power and portable DCO for SoC applications

 Duo-sheng,Ching-che

Mainly Focusing on reducing noise level and distortion on the output wave and tries to optimize to higher degree at the cost of complex implementations

September 2012

ROM-less DDFS system using 16-segment parabolic polynomial interpolation

Journal Published by ComputMath methods ,authored by Hsi-chin-His

Concentration on recent and future development of DDFS is mainly focused. Paved way for a clear understanding of DDFS and helped us in improvisation of the project as well

December 2013

Existing system

• In the existing system, there is no algorithm for

improving delay when the value of M is bulky.

• The size of the LUT increases as the number of

bits n increases.

Proposed system

• In the proposed system we modify the LUT to

increase the frequency.

• Methods for handling delay and reducing

Truncation error is also provided.

• The waveform can be varied by varying the LUT

variable available in the code.

Frequency tuning equations

• The frequency of the output sine wave is given by

fout = (M * fclk )/ 2n .

Where n=nth bit and M=forward value.

• The output wave will have frequency specified in

the range as

fout = (∆p * fclk )/2n .

Numerically Controlled Oscillator

• This is a part of DDFS, whose function is vital.

• The most scope of the project lies within NCO.

• It is a 3rd generation frequency synthesis technology.

N-BIT Freque

ncy Regist

er

N-BIT Phase regist

er

Sine Lookup Tabl

e

DACFSW

FClk

Phase Accumulator NCO

O/P

Filter

Specification Of NCO

S.No SPECIFICATION PARAMETER VALUES

1. Phase resolution (Bits) 9

2. Spur level(dB) 54.18

3. Frequency Resolution(Bits) 24

4. Output signal Sine & Cosine

5. Output Data Width 9bits

Source: IOSR-JVSP volume 1,issue 5(Jan-Feb 2013)

Tools and System Requirement

• System Requirement: PC with minimum

Pentium processor and any windows OS platform.

• Tools Used: Quartus Model sim simulator

version 13.1.0.162.

Coding and algorithm

• We create two modules one for cosine and

another one for sine wave .

• Same algorithm has been adopted in both the

modules, difference lies in the aspect of passing

values into the LOOK-UP table.

• We pass the input as wire and output as register .

• Then once the input are assigned we will create

the look up table.

• We assign values up to 255 starting from 0.

Continued..

• The values in LUT will get fetched during

positive edge of the clock and that may

be assigned using Begin statements.

• Once the value has been passed and

fetched from the LUT we will disable the

sine wave by setting acc=0.

Testing

Code for Sine wave

Continued..

Module for cosine wave

RTL Schematic

RTL schematic of NCO along with PA and Delay

units

Waveform and simulation

Sine wave been generated at 10KHZ

Sine wave at frequency less than 10KHZ

Continued..

Sine wave at 1KHZ

Continued..

Truncated Phase Wave

Continued..

Application

DDFS is mainly used in

• Modern communication receivers.

• Function generators and Signal Mixers.

Conclusion

• The DDFS models have been successfully created,

implemented and simulated using ModelSim

simulator.

• These models have effectively shown the effect of

each building block of the DDFS on the output.

• Though the generated waveform is optimized, the

LUT could not handle large bits still and

complexity increases as n-bit goes up.

• Hence that limitation has been taken as a future

improvement to reduce delay and complexity for

larger bit words.

Future work

•Since the length of the phase

accumulator is long and fetching

includes little higher delay we need to

optimize it still to a greater extend.

References

• Nehal.A.Ranabhatt,Sudhir Agarwal,Priyesh.P.Gandhi and

Raghunandh.k.Bhattar(2013),“Design and

implementation of numerically controlled oscillator on

FPGA “, Proceedings of IEEE ISSN NO:978-1-4673-599.

• DDS Technology- Online Available WWW:

http://www.hit.bme.hu/~papay/sci/DDS/start.htm.

• “Direct Digital Synthesizers: Theory, Design and

Applications”- Jouko Vankka ,Boston London , Kluwer

Academic Publishers, 2001 .

THANK YOU