DTMF detection using Goertzel algorithm

• GUIDE: Dr.M.ASHARANI Professor,ECE Department.

BYJ.RAJASEKHAR,09011D0603,M.Tech (DSCE).

Current problem and proposed solution

• Existing scenario– For DTMF detection in embedded equipment separate

ASIC need to be used. – In FPGA based designs either we have to put external

ASIC or use some complex algorithm• FFT is one approach for DTMF detection in FPGA, but which is

high area consuming

• Proposed solution– Architecture wise area efficient solution is achieved by

using Goertzel algorithm– Further area optimzed solution is achieve by using

resource sharing approach

Aim of the project

• Implementing FPGA suitable DTMF architectures– Area optimized Gortzel algorithm– Gortzel algorithm further area optimized using

resource sharing approach

DTMF detection by Goertzel technique

DTMF test signal

generator

Hex key pad Additive

white Gaussian

noise

Chipscope ILAChipscope ICON

JTAG

• In a DTMF signaling system a combination of two frequency tones represents a specific digit, character (A, B, C or D) or symbol (* or #).

• Two types of signal processing are involved:– Coding or generation.– Decoding or detection.

• For coding, two sinusoidal sequences of finite length are added in order to represent a digit, character or symbol.

DTMF Signaling

DTMF Tone Generation

• Example: Button 5 results in a 770Hz and a 1336Hz tone being generated simultaneously.

11 22 33

665544

77 88 99

##00**

AA

BB

CC

DD

1209Hz1209Hz 1336Hz1336Hz 1477Hz1477Hz 1633Hz1633Hz

697Hz697Hz

770Hz770Hz

852Hz852Hz

941Hz941Hz

11 22 33

665544

77 88 99

##00**

AA

BB

CC

DD

13361336770770770770770770770770 133613361336133613361336

Freq (Hz)Freq (Hz)

Ou

tput

Ou

tput

• Detection of tones can be achieved by using a bank of filters or using the Discrete Fourier Transform (DFT or FFT).

• However, the Goertzel algorithm is more efficient for this application.• The Goertzel algorithm is derived from the DFT and exploits the periodicity of the phase factor,

exp(-j*2k/N) to reduce the computational complexity associated with the DFT, as the FFT does.

DTMF Tone Detection

Goertzel algorithm implementation

Conventional FIR filter structure requires higher order for narrow band Pass filtering,

Goertzel algorithm extracts the peak of the signal at the specified frequency component with less hardware

• To implement the Goertzel algorithm the following equations are required:

Goertzel Algorithm Implementation

Goertzel algorithm implementation

Goertzel algorithm Is second order recursive algorithm.

Only needs two real multiplications and three real additions

• Finally we need to calculate the constant, k.• The value of this constant determines the tone we are trying to detect and is given

by:•

Goertzel Algorithm Implementation

• Where: ftone = frequency of the tone.fs = sampling frequency.N is set to 205.

• Now we can calculate the value of the coefficient 2cos(2**k/N).

Goertzel Algorithm Implementation

Goertzel Algorithm Implementation

• The feedback section has to be repeated N times (N=107).

• Since we are only interested in detecting the presence of a tone and not the phase we can detect the square of the magnitude:

Goertzel Algorithm Implementation

• The Goertzel algorithm is modified further based on the matched filter concept to achieve DTMF detection.

• The energy of the incoming signal is calculated at the eight DTMF frequencies. The DTMF frequency at which the incoming signal has maximum energy is the detected frequency.

DTMF detection by Goertzel technique

DTMF test signal

generator

Hex key pad Additive

white Gaussian

noise

Chipscope ILAChipscope ICON

JTAG

Ouput wave form hex key values found

Ouput wave form of hex key values found

Components dtmf detection using geortzel algorithum

• Direct digital frequency synthesizer

Basic Principle of DDFS

SpecificationsThe following specifications are considered for

design and implementation of the DDFS.1) Types of signals : sine.

2) Type of signal synthesis : ROM based DDFS

3) phase resolution chosen in DDFS :5.625O

5) front end design entry : VHDL

(6) Backend synthesis : Xilinx Spartan 3E FPGA

Tools and hardware

• Simulation software - Modelsim Xilinx Edition (MXE)

• Synthesis, P&R - Xilinx ISE • On chip verificaiton - Xilinx Chipscope

• Hardware – Xilinx Spartan 3 Family FPGA board

Applications

• Embedded long distance control signal transmission

• New telephone and voice chipsets

• FPGA based security applications

Advantages

• Low area solution in comparison with conventional FFT approach

• FPGA implementation allows further logic to be added for realizing CSOC (configurable system on chip) designs

References

• DTMF detecion with Goertzel algorithm using FPGA, a resouce sharing approach, Kamal Shaterian, Hossein gharaee, IEEE 2010

• Texas Instruments. ‘‘Modified Goertzel algorithm for DTMF using the TMS320C80’’, application report spra066. 1996