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Suvarna Joshi et al. / International Journal of Engineering Science and Technology

Vol. 2 (12), 2010, 7320-7323

FPGA BASED FIR FILTER

SUVARNA JOSHI1

Computer Engg. Department, MIT College of Engg, Pune,

[email protected]

BHARATI AINAPURE2

Computer Engg. Department, MIT College of Engg,Pune,

[email protected]

Abstract: This paper gives brief overview of the basic structure and hardware characteristics of the FiniteImpulse Response (FIR) digital filter.FIR filter has been designed efficiently using matlab and implemented onField Programmable Gate Array (FPGA) platform. MATLAB FDATool has been used to determine filtercoefficients and 4th order 32 bit filter has been prototyped. The design has been prototyped on an XC3S500-4FG320 in Spartan-3E Platform using Integrated Synthesis Environment (ISE) 9.1/10.1 Tools all in one designsuit from Xilinx.

Keywords-FIR,FPGA, FDATool, Xilinx

1 .IntroductionFilter as the name indicates remove unwanted components of signal. Filters are used for extraction of

desired signal from noisy signal which consist of unwanted disturbances. Filters can be broadly described as a

signal selection system. In the digital era, the digital filter, which has attracted people’s broad attention more

and more, has been widely applied to communication, voice, image, automatic control, radar, aerospace,

medicine and so on. As compared to analog filters, digital filters are having higher precision, better stability and

reliability. Digital Filters do not have matching problems. Digital filters represent time division multiplexing

which can complete some filtering tasks that a number of analog filters is incapable of doing. We can achieve

digital filters by hardware circuits. Also we have an alternative approach as computer software programming.

[Jiang(2010)] There are two types of digital filters Finite impulse response filter and infinite impulse response

filters. Speaking from the realization, IIR adopts recursive structure and uses the rational fraction which is equal

to the ratio of two polynomials approximate to the frequency character, so it is able to get better frequency

selection characters by use of less order.But it is gained at the cost of the non-linear phase characters. At the same time, the existence of

feedback slip requires the higher system stability and easily causes oscillation. Compared with the Infinite

Impulse Response (IIR), the FIR filter is capable of meeting the strict requirements of the amplitude and phase

characters, avoiding the drift and noise and so on, which is generated by the IIR filter, is easily achieved by

hardware and has the precise linear-phase and high system stability. In recent years, with the rapid development

of the Very Large Scale Integrated (VLSI) technology, FPGA (Field programmable gate array)[Zhang(2006)] has

been widely applied because of its reprogramability, reconfigurability, low-cost, high logic density and high

reliability. FPGA, the structured internal logic array and rich connection resources, particularly can be useful to

the digital signal processing. FPGA is a programmable logic device which is having user programmable

features. This actually can minimize system design risk and maintenance and shorten the design cycle. To

enhance system speed and reducing implementation complexity a lot of work have been done in the process of

achieving digital signal processing by use of the FPGA.FIR algorithm can use the software to achieve in the

Digital Signal Processor (DSP) or Central Processing Unit (CPU), but in a number of systems demanding high

real-time, because of the ordinal implementation of the procedures, the software based on real-time often cannotmeet the requirements. So it must use hardware to achieve a high speed. Now FPGA becomes a good

choice.[Jieshan(2009)]

2..Basic principle of FIR filter

The impulse response h (n) of finite unit impulse response filter with sequence of length N, the transfer

function usually has the following from [Jiang (2010)]:

…. (2.1)

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Vol. 2 (12), 2010, 7320-7323

Differential equation can be described as

…. (2.2)

As it can be seen from the differential equations(2.2)[Jieshan(2009)], FIR filter order is N-I, length is N. System

output depends on a function of the input, and has no direct relationship with the past output, it does not contain

feedback branch. y(n) is the output. [Jiang (2010)] And x(n-i) is the input sample sequence on the nth times. h(i) isthe i-th level filter tap coefficient, L is the number of the filter tap. Its basic structure is shown in Fig. 1

[Jieshan(2009)]. We can find that the structure of FIR filter in hardware is mainly composed of the shift register,

adder and multiplier.

Fig. 1. N-order FIR digital filter block diagram [Jieshan(2009)]

3. FIR filter DesignFIR filter has been designed using Window method. The basic design principles of window function are to

calculate hd(n) by the anti-Fourier transform based on the ideal demanded filter frequency response Hd(ejw).

The formula of hd(n) is as follows in (3.1) [Jieshan(2009)]:

….(3.1)

Because hd(n) is infinitely long, we have to deal with it by the window function to get to the unit impulse

response h(n) which meets the requirement. Its calculation formula is shown in (3.2). w(n) is the windowfunction.

…. (3.2)

FIR filter coefficients has been found from the method of window function, the basic idea of window function

is to have the narrowest main lobe width and side lobes as small as possible, so we use Hamming window for

the filter design. Matlab special toolbox FDATool (Filter Design & Analysis) has been used to simulate and

design filter[Zhang(2006)], the filter amplitude-frequency characteristics meet the requirements .The filter

coefficients exported to a text file, 4-order impulse response coefficients of FIR filters are as follows:

FIR Filter Design parameters has been given as follows

1) Order of filter - 4

2) Window type-hamming window

3) Sampling Frequency fs=48000

4) Cut off frequency fc=10800

5) Input data size-32 bit

6) Filter Coefficients

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Vol. 2 (12), 2010, 7320-7323

Table 1 Filter Coefficients for low pass and high pass filter

Low Pass High Pass

-0.0037453391408711189 -0.0055441199344672806

0.02658205770921216 -0.074845619115308265

0.45040671298934842 0.83799343436458384

0.02658205770921216 -0.074845619115308265

-0.0037453391408711189 -0.0055441199344672806

4. Filter simulation and implementation detailsVery high speed hardware description language (VHDL) has strong abstract description ability to

support hardware design, verification, synthesis and testing. VHDL can describe the same logic function in

multiple levels, such as it can describe the structure of the circuit composition in the register level and describe

the function and performance of the circuit in the behavior level. VHDL has been used to enter hardware

description of fir filter. The implementation has been done on a FPGA platform. The filter design has been

prototyped on an XC3S500-4FG320 FPGA device in Spartan-3E Platform using ISE 9.1/10.1, tools all in one

design suit from Xilinx.

5. Simulation Results

Fig.2 Simulation results of fir filter

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Fig 3 Simulation results of addition module

Fig 4. Simulation results of multiplier module

ConclusionThis paper mainly describes the design and simulation of FIR filter which is based on FPGA, XILINX tools

and Matlab.By using these tools time required to get desired results has become less.FIR filter coefficients design

has been performed by using FDATool. VHDL has been used to enter hardware description. VHDL codes have been

written, synthesized, mapped then successfully configured and prototyped. FIR filter designed fully complies with

design requirements.

References[1] Jiang Xiaoyan and Bao Yujun , “FIR Filter Design Based on FPGA”, 20IO International Conference on Computer Application and

System Modeling (ICCASM 2010),

[2] Jieshan Lin and Huang Shizhen, “An Design of the 16-order FIR Digital Filter Based on FPGA”, 2009, International Conference on

Information Science and Engineering (ICISE2009)

[3] Zhang Chi and Guo Li Li, Design of FIR filter with Matlab and running on FPGA, Applied Science and Technology. vol. 33, no. 6,

pp.83, Jun. 2006

[4] http://www.mathworks.com/help/toolbox/signal/fdatool.html[5] S. Salivahanan, A. Vallavaraj,”Digital Signal Processing ”,Tata McGraw Hill Publishing company,New Delhi, 2007

[6] Rudra Pratap ,”Getting started with MATLAB 7: a quick introduction for scientists and engineers”, Oxford University Press, 2006

[7] Volnei A .Pedroni,”Circuit Design with VHDL”,,MIT Press Cambridge,London,England,2004

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IJEST10-02-12-191