scholarly journals Sharpening of the multistage modified comb filters

2011 ◽  
Vol 8 (3) ◽  
pp. 281-291 ◽  
Author(s):  
Marko Nikolic ◽  
Miroslav Lutovac
Keyword(s):  
Comb Filter ◽  
Polyphase Filter ◽  
Filter Structure ◽  
Direct Form ◽  
Comb Filters ◽  
Decimation Filter ◽  
Last Stage ◽  
Positive Integers

This paper describes the application of filter sharpening method to the modified comb filter (MCF) in the case of decimation factor, which is product of two or more positive integers. It is shown that in the case of multistage decimation with MCF, filters in each stage are also MCF. Applying the sharpening to the decimation filter in the last stage provides very good results, with savings in the number of operations comparing to the case of sharpening of the complete filter. Direct-form FIR polyphase filter structure is proposed for the filters in each stage.

Methods for Improving Alias Rejections in Comb Filters

2018 ◽  
pp. 4746-4760
Author(s):  
Gordana Jovanovic Dolecek
Keyword(s):  
Chebyshev Polynomials ◽  
Sampling Rate ◽  
Comb Filter ◽  
Comb Filters ◽  
Decimation Filter

Downsampling is the process of decreasing the sampling rate of signal by an integer. This process may introduce the unwanted spectrum replica called aliasing. To avoid aliasing the signal must be filtered by decimation filter prior downsampling. Decimation consists of filtering and downsampling. The most simple decimation filter is comb filter usually used in the first stage of decimation. However, comb filter does not provide a good aliasing rejection. This paper presents the methods for improving alias rejection of comb filters. The methods are based on comb zero rotation, cosine filters, Chebyshev polynomials, and cascade of combs with different parameters.

Methods for Improving Alias Rejections in Comb Filters

2019 ◽  
pp. 891-909
Author(s):  
Gordana Jovanovic Dolecek
Keyword(s):  
Chebyshev Polynomials ◽  
Sampling Rate ◽  
Comb Filter ◽  
Comb Filters ◽  
Decimation Filter

Downsampling is the process of decreasing the sampling rate of signal by an integer. This process may introduce the unwanted spectrum replica called aliasing. To avoid aliasing, the signal must be filtered by decimation filter prior to downsampling. Decimation consists of filtering and downsampling. The simplest decimation filter is comb filter usually used in the first stage of decimation. However, comb filter does not provide a good aliasing rejection. This chapter presents methods for improving alias rejection of comb filters. The methods are based on comb zero rotation, cosine filters, Chebyshev polynomials, and cascade of combs with different parameters.

Methods for Simultaneous Improvement of Comb Pass Band and Folding Bands

2018 ◽  
pp. 6171-6183
Author(s):  
Gordana Jovanovic Dolecek
Keyword(s):  
Design Methods ◽  
Comb Filter ◽  
Signal Spectrum ◽  
Pass Band ◽  
Original Spectrum ◽  
Compensator Design ◽  
Decimation Filter

This decimation introduces the replicas of the main signal spectrum. If the signal is not properly filtered, the overlapping of the repeated replicas of the original spectrum, called aliasing, may occur. The aliasing may destroy the useful information of the decimated signal and must be eliminated by the filter which precedes the decimation, called decimation filter. The most popular decimation filter is a comb filter, usually used in the first stage of decimation. However its magnitude characteristic is not flat in the pass band of interest and there is not enough attenuation in the folding bands. Different methods are proposed to improve comb magnitude characteristic. This article presents an overview of methods for simultaneous improvement of comb magnitude characteristic in both: pass band and folding bands. The methods are divided into three main groups: Sharpening-based methods, Corrector–based methods, and Methods based on the combination of alias rejection and compensator design methods.

Comb Filters Characteristics and Current Applications

2018 ◽  
pp. 6007-6018
Author(s):  
Miriam Guadalupe Cruz-Jimenez ◽  
David Ernesto Troncoso Romero ◽  
Gordana Jovanovic Dolecek
Keyword(s):  
Comb Filter ◽  
Digital Audio ◽  
Linear Phase ◽  
Phase Filter ◽  
Comb Filters ◽  
Passband Droop

The comb filter is a very popular linear-phase filter due its simplicity, i.e. all its coefficients are equal to unity. As a consequence, it does not require multipliers or coefficients storage. This characteristic makes this filter attractive for many applications, as for example, in decimation, communications, digital audio, among others. However, the comb filter presents passband droop and a poor attenuation in the stopband region. In this proposal, the comb filter characteristics are reviewed and illustrated with one example. Additionally, the selected methods commonly used to improve the magnitude characteristics of a comb filter will be described and illustrated with examples.

scholarly journals Border Handling for 2D Transpose Filter Structures on an FPGA

2018 ◽  
Vol 4 (12) ◽  
pp. 138 ◽  
Author(s):  
Donald Bailey ◽  
Anoop Ambikumar
Keyword(s):  
Signal Processing ◽  
Digital Signal Processing ◽  
Digital Signal ◽  
Linear Filters ◽  
Filter Structure ◽  
Direct Form ◽  
Two Stages ◽  
Filter Structures ◽  
Zero Extension

It is sometimes desirable to implement filters using a transpose-form filter structure. However, managing image borders is generally considered more complex than it is with the more commonly used direct-form structure. This paper explores border handling for transpose-form filters, and proposes two novel mechanisms: transformation coalescing, and combination chain modification. For linear filters, coefficient coalescing can effectively exploit the digital signal processing blocks, resulting in the smallest resources requirements. Combination chain modification requires similar resources to direct-form border handling. It is demonstrated that the combination chain multiplexing can be split into two stages, consisting of a combination network followed by the transpose-form combination chain. The resulting transpose-form border handling networks are of similar complexity to the direct-form networks, enabling the transpose-form filter structure to be used where required. The transpose form is also significantly faster, being automatically pipelined by the filter structure. Of the border extension methods, zero-extension requires the least resources.

scholarly journals Continuously Wavelength-Tunable First-Order Narrowband Fiber Comb Filter Using Composite Combination of Wave Retarders

2020 ◽  
Vol 10 (18) ◽  
pp. 6150
Author(s):  
Jaehoon Jung ◽  
Yong Wook Lee
Keyword(s):  
Principal Axis ◽  
Beam Splitter ◽  
Orientation Angle ◽  
Comb Filter ◽  
First Order ◽  
High Birefringence ◽  
Filter Structure ◽  
Half Wave ◽  
Quarter Wave ◽  
Polarizing Beam Splitter

Here, by harnessing a composite combination of wave retarders, we propose and experimentally demonstrate a first-order narrowband fiber comb filter capable of continuously tuning its wavelength, of which the filter structure is on the fundamental basis of a polarization–diversity loop structure. The demonstrated comb filter consists of a polarizing beam splitter (PBS), two high birefringence fiber (HBF) segments of the same length, an ordered wave retarder combination (WRC) of a quarter-wave retarder (QWR) and a half-wave retarder (HWR) before the first HBF segment, and an ordered WRC of an HWR and a QWR before the second HBF segment. The second HBF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. Taking the filter transmittance obtained by Jones calculus into consideration, we found the azimuth orientation angle (AOA) sets of the four wave retarders, which could allow extra phase shifts (ψ’s) ranging from 0° to 360° to be induced in the narrowband transmittance function. From filter transmission spectra calculated according to the AOA sets found above, it is confirmed that the first-order narrowband comb spectrum can be continuously tuned by properly controlling the AOA’s, clearly indicating the continuous wavelength tunability based on a composite combination of ordered wave retarders. This theoretical prediction was verified by actually constructing the proposed filter. Then, it is concluded that our filter employing the composite combination of wave retarders can be continuously frequency-tuned by properly controlling the AOA’s of the wave retarders.

scholarly journals A VLSI DSP DESIGN AND IMPLEMENTATION OF COMB FILTER USING UN-FOLDING METHODOLOGY

2012 ◽  
pp. 72-77
Author(s):  
PURU GUPTA ◽  
TARUN KUMAR RAWAT
Keyword(s):  
Signal Processing ◽  
Computation Time ◽  
Digital Signal ◽  
Vlsi Circuits ◽  
Comb Filter ◽  
Destructive Interference ◽  
Sample Period ◽  
Iteration Bound ◽  
Comb Filters ◽  
Digital Waveguide

In signal processing, a comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. Comb filters are used in a variety of signal processing applications that is Cascaded Integrator-Comb filters, Audio effects, including echo, flanging, and digital waveguide synthesis and various other applications. Comb filter when implemented has lower through-put as the sample period can not be achieved equal to the iteration bound because node computation time of comb filter is larger than the iteration bound. Hence throughput remains less. This paper present the comb filter using one of the methodology needed to design custom or semi custom VLSI circuits named as Un-Folding which increases the throughput of the comb filter. Un-Folding is a transformation technique that can be applied to a DSP program to create a new program describing more than one iteration of the original program. It can unravel hidden con-currency in digital signal processing systems described by DFGs. Therefore, unfolding has been used for the sample period reduction of the comb filter for its higher throughput.

scholarly journals Design of CIC based decimation filter structure using FPGA for WiMAX applications

2019 ◽  
Vol 16 (7) ◽  
pp. 20190074-20190074
Author(s):  
V. Jayaprakasan ◽  
S. Vijayakumar ◽  
Pandya Vyomal Naishadhkumar
Keyword(s):  
Filter Structure ◽  
Decimation Filter

Comb-Based Filters for Sampling Rate Conversion

2009 ◽  
pp. 316-346
Author(s):  
Ljiljana Milic
Keyword(s):  
Communication Systems ◽  
Moving Average ◽  
Sampling Rate ◽  
Software Radio ◽  
Satellite Communications ◽  
Comb Filter ◽  
Single Chip ◽  
Comb Filters ◽  
The Individual ◽  
Rate Conversion

Comb filters are developed from the structures based on the moving average (boxcar) filter. The combbased filter has unity-valued coefficients and, therefore, can be implemented without multipliers. This filter class can operate at high frequencies and is suitable for a single-chip VLSI implementation. The main applications are in communication systems such as software radio and satellite communications. In this chapter, we introduce first the concept of the basic comb filter and discuss its properties. Then, we present the structures of the comb-based decimators and interpolators, discuss the corresponding frequency responses, and demonstrate the overall two-stage decimator constructed as the cascade of a comb decimator and an FIR decimator. In the next section, we expose the application of the polyphase implementation structure, which is aimed to reduce the power dissipation. We consider techniques for sharpening the original comb filter magnitude response and emphasize an approach that modifies the filter transfer function in a manner to provide a sharpened filter operating at the lowest possible sampling rate. Finally, we give a brief presentation of the modified comb filter based on the zero-rotation approach. Chapter concludes with several MATLAB Exercises for the individual study. The reference list at the end of the chapter includes the topics of interest for further research.

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