Efficient Design of Higher Order Variable Digital Filter for Multi Modulated Signals

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 4 ISSUE 2 – APRIL 2015 - ISSN: 2349 - 9303

Efficient Design of Higher Order Variable Digital Filter for Multi Modulated Signals P.D.Swathika1 PG Scholar, Sona College of Technology, VLSI Design, Salem, India1. swathikadhanapal@gmail.com Abstract— The electrocardiogram (ECG) analysis is commonly used technique in clinical examination proposes a method of designing reconfigurable warped digital filter with various low-pass, high-pass, band-pass and band-stop responses. The warped filter is obtain by replacing each element interruption of a digital filter with an all exceed filter. It is widely used for various video and audio processing applications. Warped filters require first-order all pass conversion to obtain low-pass and high-pass responses, and by using second-order all pass conversion to obtain variable band-pass and band-stop responses. To overcome this drawback, proposed method combines warped filters with the coefficient decimation technique. In VLSI circuits in order to reduce hardware cost Command Signals Decoder (CSD) based shift-and-add approach is used for multiplication. It offers extensive savings in opening count and power utilization more than other approaches. Index Terms— Variable Digital Filter, Warped Filter, All Pass Filters, Command Signals Decoder

1 INTRODUCTION Various types of ECG analysis works with biomedical applications started in late 1950’s, and each year a greater amount of recording are acquired and analyzed. So, automatic ECG analysis is a topic that continues to be of interest in biomedical engineering. The warped filter structure is designed only with linear-phase FIR and sub-filter coefficients. These sub-filters are related, with fractional delays [1]. The filter design is more difficult as the number of unknown parameters is larger, for (eg). 42686 parameters with 3048 channels, optimization problem occurs due to the higher-order design [2]. In order to reduce the channel parameter, design structure gives 21343 channels. Hence it posses huge memory resources and complexity of time in higher-order filters. The transmit function of FIR filter order which will increase the difficulty [1] [2] and the clean signal in contribution dispensation sampling rate also increases the amount of time. The applicability of unknown parameters of higher-order [3] is designed through filter banks and fractional delays. The existing technique shows the design of individual low pass filters and flexible modulated filter banks [1], with Transmultiplexers TMUX [3] [5]. The major disadvantage of this method is that it cannot be applicable for all types of filters and its filter structure. It makes the implementation of polynomial impulse response [4] respect to direct form linear-phase FIR filters, with a narrow transition

band is mainly expensive when compared with variable digital filters. The existing technique that works with Modified Discrete Fourier Transform MDFT) filter banks are introduced. It shows the analysis of using synthesis filters with modulation of complex low-pass prototype filters in subbands comparisons. The existing mappings of MDFT filter banks [6], real input signals are converted to complex subbands signals by the reconstruction of prototypes with linear-phase structure. Then MDFT filter banks are changed to complex modulated, critically sub sampled by DFT filter banks. They combine key features of DFT filter banks as linear phase analysis and synthesis filters and an efficient realization with almost [7] Perfect Re-construction (PR).However in many applications, the functions of the polyphase components with single-stage structure results in substantially higher complexity when compared with proposed formation. Hence the further cost is obtained by converter block of fractional delay coefficient with delayed functions [2]. Hence the filter banks works unequally for conversions of multistage converters which shows poor flexibility condition. The proposed method includes reconfigurable warped filter structure with all pass filters are designed with variable digital filters in order to yield a Fetal ECG output from MotherECG input signal with respective cut-off frequencies.

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i.e., the difference between the pass band and stop band edges, as well as the pass band/stop band ripples. In both cases, the filter order is more sensitive to the transition band rather than the ripples. After estimating the filter order, one must solve an optimization problem to determine the filter coefficients. For high filter orders, e.g., 32767 which is used in a cosine modulated filter bank (CMFB) with 2048 channels the filter design becomes difficult as the number of [6][7] unknown parameters is large. Relations between the filter order and the number of FB channels, is not crucial. In other words, the main aim to show the effectiveness of obtaining filters with high orders. To overcome this drawback, proposed method includes variable digital filters for multimodulated processing with flexible input coefficients.

RELATED WORKS

The concept of farrow structure with fractional delays was used in order to achieve for [6][7] generating perfect-reconstruction (PR) multichannel prototype finiteimpulse response. The synthesis of transfer function with linear-phase FIR is given by -n đ??ťp(z) = đ?‘ đ?‘›=0 â„Ž p n z Where hp [N-n] = hp[n] for n=0, 1 ‌N. The impulse response to the transfer function Hk (z) is denoted as the reference prototype filter followed by Cosine- modulation is â„Žđ?‘˜[đ?‘›] =â„Žđ?‘?[đ?‘›]

1 đ?œ‹

2/đ?‘š

* cos [(k + )

2 đ?‘€

đ?‘

đ?œ‹

2

4

(n- ) + (-1) k ]

For generating PR with CMFB based prototype filters for given number channels, in order to guarantee PR condition independent. The values of these design unknowns are selected with its requirements. Based on prototype filter PR with CMFB has no constraints to minimize the objective function. These facts are unable to use of any effective unconstrained prototype filters. However, due to the fact of these problems, the convergence with local optimum solution implies a poor enough in linear-phase FIR structure.

4

PROPOSED METHODOLOGY

Direct Arithmetic (DA) based approach is used for filter convolution with this approach we can increase the filter response speed without adding any hardware complexity. For sharp filter response requires a large number of coefficients (impulse responses). This will increase the filter length and more filter taps are required for computation. Here through decimation factor taps used for filter output is changed dynamically.

3 EXISTING METHODOLOGY FARROW STRUCTURE

4.1 Proposed Variable Digital Filter The Farrow Structure is used to express the filter design of a linear phase FIR [1]. Methods of designing these high-order normalized filters are prototype filter banks (FB’s) and transmultiplexers (TMUX) with large number of channels. Here the performance of filter is not analyzed. The farrow structure consists of sub filters with different set S L (z) = 0, 1‌.L.

Variable Digital Filters (VDF) is digital filters with controllable spectral characteristics such as cutoff frequency response, adjustable pass band width, and controllable fractional delays. They found applications in different areas of signal processing and communications, e.g. fractional delay digital filters for timing adjustment in digital receivers. In proposed system, variable digital filters are designed by using warped filter structure. Variable digital filters is a filter whose frequency response specifications, cutoff frequency fc can be controlled through number of parameters with minimum overhead on complexity. Methods for designing variable digital filters are done by using conversion method. Certain conversion such as all pass conversion is then applied to VDF with variable cutoff frequencies. The coefficients of the polynomials are then determined to provide continuous tuning of the VDF by conversion. The z-domain transfer function obtained from the bilinear transform is at best a good approximation of the analog frequency response. As the input frequency increases toward fs/2, the digital filter response becomes less representative of the analog frequency response. The decimation technique is denoted by the simplest resampling technique because it involves reducing the number of samples per second required to represent a signal. If the input signal is strictly band limited such that the signal spectrum is zero for all frequencies above fs/ (2M), then decimation can be performed by simply retaining every M-th sample method.

x (n)

S2(z)

SL(z)

Îź

S1(z)

Îź

S0(z)

Îź y (n)

Fig.1. Farrow Structure By using 16-bit multipliers in each filter tap consume large area and power. Hence overall throughput is very poor in multiplier based approach and it has less accuracy in computing difference between input and reference signal in filter block. Linear-phase FIR filters irrespective of its regulate being high, low, even, or odd as well as the impulse response being symmetric or antisymmetric. However, it is more difficult for filters with high orders as the conventional design of such filters is more challenging. High computational delay shows implementation complexity is high. The order of a linear-phase finite-length impulse response (FIR) low pass filter depends on its transition band,

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 4 ISSUE 2 – APRIL 2015 - ISSN: 2349 - 9303 Fs1

complexity of the band pass filter uses second-order all pass conversion.

Fs2

A (Z)

Input

Frequency selection Input

Z-1

Output

+

Output +

Z-1

Input filter coefficients

�

MECG input signal

Alpha value for cut off frequency selection

_

Extracted FECG output

All pass filter structure using MUX

Fig.4.Single multiplier structure for A (z) The approximation function is assumed to be a linear combination of filter structure. Without loss of complexity, a tunable adaptive filter using a piecewise polynomial yields tunable FIR VDF with good frequency characteristics and offers larger tuning range than ordinary polynomial-based approach. They include conversion based on warped filter and frequency response masking based approach. Coefficient decimation (CDM) technique for realizes the low-complexity. VDFs with fixed coefficients are designed using warping technique to detect bandpass signals in a broadband signal. The variable frequency of Îą coefficients are obtained as Low-pass frequency responses are obtained using the all pass transformation given by

M-Decimation factor

Fig.2. Block Diagram of VDF

4.2

Warped Îą- Coefficient Frequency Variation

Warped filter is obtained by replace each unit impediment of a digital pass through a filter with all-pass structures of an appropriate order. Therefore by changing the coefficients of an all pass filters, the fc can be controlled.

−đ?›ź+đ?‘§ −1

G (z) = H (A (z)). Where A (z) = (1−đ?›źđ?‘§ −1 ) |Îą| < 1 High-pass frequency responses are obtained using the all pass transformation given by G (z) = H (-A (z)). Fixed bandwidth band-pass responses at an arbitrary center frequency are obtained by using the reduced second order transformation given as

X (n)

h0

h1

h2

+

hn

−đ?›ź+đ?‘§ −1

A(Z)

A(Z)

G (z) = H (B (z)). B (z) = -z-1 (1−đ?›źđ?‘§ −1 ) Where |Îą| < 1 = -z-1 A (z). Fixed bandwidth band-stop responses at an arbitrary center frequency are using the transformation given as G (z) = H (-B (z)). In proposed VDF, there are two controlling parameters used such as warping coefficient Îą and decimation factor M. Both the parameters control the cutoff frequency Îą controls the center frequency and M controls the bandwidth |Îą| < 1 and M can be used as a positive integer. In the same way, different kinds of variable responses can be obtained using fixed coefficient filter architecture.

A(Z) Y (n)

�

Fig.3. Warped digital filter Warped filters bandwidth needs to be changed, to update the filter coefficients which will incur a large number of memory read and write operations. Depending on the application, warped filters with response of low-pass, high-pass, bandpass or bandstop are designed. Here alpha is a set of constants used to vary the cutoff frequency selections of all pass filters.

4.4 Fetal ECG Extraction

4.3 Frequency Responses of All Pass Filters Design

The adaptive algorithms for FIR filters are widely used in various applications such as medicine, statement and have power over due to its easily performance, strength and best presentation. Its simplicity makes it attractive for ECG analyses where it is need to minimize MECG error response. Filters take part in a significant role for exclusion of

A filter bank designed using warped filters is proposed for all pass filters. The low pass, band pass, and high pass filters are connected in parallel. However, the

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 4 ISSUE 2 – APRIL 2015 - ISSN: 2349 - 9303 redundant signal or clamor from unique input signal in FECG extraction by removing the selected frequencies from the incoming signal. These FECG signals become much popular due to the amplification of the digital signal processing. Here a comparator is used to acquire finite response between input signal and desired response signal. The comparator output is reorganized in LUT and multiplied with samples as filter coefficients.

The above figure shows the reference signal and input signal obtained from MECG samples. The sample is loaded into an on chip memory with width 15bit and depth of 1000 and applied to internal logical blocks by using a sequential 10bit counter. The output shows the testbench wave forms in which the signal coefficients have been fixed. Simulation is obtained using modelsim simulator.

4.5 Adaptive Filters with Low Complexity Filters are used in application of biomedical instruments, as the frequency response of medical instrument are extremely small and so digital filters are much accepted for low rate of recurrence application. The manipulative of the adaptive filter, it’s balanced to choose the adaptive filter algorithm for high accuracy. Here LMS algorithm is proposed with AFIR for Fetal ECG extraction, which will be interior causative factor for the achievement of algorithm functioning. For any purpose of the adaptive filters, the contribution signal and the orientation effort is essential to individual progression. The smallest amount indicates squaring method is use to regulate the influence of the adaptive filter in order to decrease the error. The best explanation to remove the unnecessary signal or noise from the participation signal is the suggestion noise must be cleaned out by means of adaptive filtering technique due to its good concert and consistency. The filter coefficients in adaptive filtering are a set of constants which is used to multiply delayed signal samples inside the structure. FIR filter is terminated by its transfer function and the filter order is merely the number of taps multiplied by MAC unit, if suppose response is working until now the desire reaction is said to be finite, the filter still is a FIR. This pass through a filter have a limited desire response constant while it uses opinion after N samples of an desire function represented in digital filtering.

5.

Fig.6. Simulation of FECG Extraction The figure shows accurate fetal ECG extracted from MECG. Low frequency component and distortions are removed using HP filter and genetic algorithm by coefficient replacement. Based on its time and frequency, the conditions of fetal can be analyzed.

6

RESULTS AND DISCUSSION

The input MECG signal is referred to the concentration of detecting QRS- complex with adaptive equalization of binary test noise obtained by warped filters. This is the prominent feature in ECG recordings and it is still deemed to be useful information about the heart status of patients recently more complete algorithms that allow the computation of other essential ECG parameters have been developed.

SIMULATION RESULTS & ANALYSIS

Fig.7. Result of FECG separation.

Fig.5. Simulation of MECG

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INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY VOLUME 4 ISSUE 2 – APRIL 2015 - ISSN: 2349 - 9303 modulated transmultiplexers based on the frequencyresponse masking approach” IEEE Trans. Circuits Syst. I, vol. 52, no. 11, pp. 2413–2426, Nov. 2005.

7. CONCLUSION In this paper, variable filter design using warped filters has been presented. Most of these VDFs are commonly used for communication applications due to their exact characteristics of warped structure with all pass filters and flexible input coefficients. It has been considered to denoised the filters from the noisy input signal with application of FECG signal get separated from MECG distortion less output obtained from all pass filter coefficients through reference input capitulate to get FECG output By using these proposed technique, FECG signal is denoised and low complexity, accuracy is achieved. All simulation results are carried out by using modelsim software.

[4] R. Lehto, T. Saramäki, and O. Vainio “Synthesis of narrowband linear-phase FIR filters with a piecewisepolynomial impulse response” IEEE Trans. Circuits Syst. I, vol. 54, no. 10, pp. 2262–2276, Oct. 2007. [5] P.Martin-Martin, R. Bregovic, A. Martin-Marcos, F. Cruz-Roldan, and T. Saramäki, “A generalized window approach for designing transmultiplexers,” IEEE Trans. Circuits Syst. I, vol. 55, no. 9, pp. 2696–2706, Oct. 2008. [6] T. Karp and N. J. Fliege, “Modified DFT filter banks with perfect reconstruction,‖IEEE Trans. Circuits Syst. II, vol. 46, no. 11, pp. 1404–1414,Nov. 1999.

REFERENCES [1] Amir Eghbali and Håkan Johansson,” On efficient design of high-order filters with applications to filter banks and transmultiplexers with large number of channels”, IEEE Trans, on signal processing, vol. 62, no. 5, march 1, 2014.

[7] R. Bregovic and T. Saramäki, ―A systematic technique for designing linear-phase FIR prototype filters for perfectreconstruction cosine- modulated and modified DFT filter banks,‖ IEEE Trans. Signal Process. vol. 53, no. 8, pp. 3193–3201, Aug. 2005.

[2] H. Johansson and O. Gustafsson,“Linear-phase FIR interpolation, decimation, and M-th band filters utilizing the Farrow structure” IEEE Trans. Circuits Syst. I, vol. 52, no. 10, pp. 2197-2207, Oct. 2005.

[8] T. Ihalainen, T. H. Stitz, M. Rinne, and M. Renfors, ―Channel equalization in filter bank based multicarrier modulation for wireless communications,‖ EURASIP J. Appl. Signal Process, vol. 2007, 2007, Article ID 49389.

[3] M. B. J. Furtado, P. S. R. Diniz, S. L. Netto, and T. Saramäki “On the design of high-complexity cosine-

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