The compensator is composed of two simple filters with sinewave form of magnitude responses. Cascaded integrator comb cic filters are used to realize computationally efficient decimation. The proposed multiplierless linear phase finite impulse response compensator works at a. Understanding cic compensation filters prerequisites this document targets digital signal processing dsp systems engineers who must design cic compensation filters for rate conversion systems. When you design either a decimator or interpolator, the resulting filter is a cic filter that decimates or interpolates your input signal. Joint cic compensation and interpolation filter design as mentioned in section 2, cic filters are an integral part of most digital decimation filter designs in software radios.
Cic filter design the antialiasing filter is the important role of decimation filter and also used to find out the less number of decimation stages that could provide useful implementation about cic filter. If n is the number of integrator and comb sections of the cic filter, then 2 n is the last section of the cic filter. The use of this design is governed by, and subject to, the terms and conditions of the hardware reference design license agreement. The name must begin with a letter and be composed of the following characters. Hogenauer filter cascade integrator comb filters informit. If not already done, install scilab free numerical computing software. Design cascaded integratorcomb cic filter simulink. Pdf software defined radio sdr or software radio is one of the most. The cic filter is used as an anti aliasing filter, when the data rate is high since the operation in the cic filter only consists of addition operation. Cic interpolation filter with multichannel data support for stratix v. In this syntax, the filter has two sections and the differential delay is 1. The overall system response is plotted for you to verify key system specifications such as the passband ripple and stopband attenuation. The script uses the frequency sampling method to design a fir filter that has an.
The inputoutput word length and fraction length are specified. Cascade integratorcomb cic filter this module is an fixedpoint implementation of cic filter with configurable parameters. Sample rate conversion filter design for multistandard. Some applications that use the cic filter include software designed radios. Digital filter designers like to see zplane polezero plots, so we provide the zplane characteristics of a d 5 cic filter in figure 4c, where the comb filter produces d zeros, equally spaced around the unitcircle, and the integrator produces a single pole canceling the zero at z 1. Department of electronics, walchand institute of technology, solapur.
The cic filter frequency response does not have a wide, flat pass band. Using cic decimation filter with multichannel support intel. The clock divider circuit is introduced between the integrator and comb filter. Cic filter constraints cic decimator filter have the following two constraints.
This paper presents multiplierless cic compensator for softwaredefined radio sdr application. Differential delay specify the differential delay of your cic filter as an integer value greater than or equal to 1. However, a cic filter followed by a short to moderate length fir or iir proves highly applicable. For instance, with 10bit input data and a 100tap boxcar filter with a gain of 100, we require 7bits of growth for a bit field width of 17bits.
Pdf design and implementation of efficient cic filter structure for. Analysis and implementation of multirate cascaded integrator. Cascaded integratorcomb cic filter cascaded integratorcomb cic filters, also known as hogenauer filters, are used to achieve arbitrary and large sample rate changes in digital systems. The cic contains two subfilters, the comb and the integrator, which can be applied in either order. For example, if a q 3stage cic decimation filter accepts onebit binary input words from a sigmadelta ad converter and the decimation factor is d 64, binary overflow errors are avoided if the three integrator and. Design multiband complex fir filters of the following types. Designing digital down conversion systemsusing cic and fir filters. Designing digital down conversion systems using cic and fir. Cascaded integratorcomb cic filter lattice semiconductor. Simulation and design of cic filter using verilog hdl intel. The cic filter block diagram is shown in figure 2 figure 2. Design of cic filters for software radio system ieee conference. Scopefir can design filters, hilbert transformers, or differentiators. If the filter is applied to an upsampling task, the comb filter is placed at the input to the cic filter.
The proposed system is to design the basic concept of the five stage cic decimation filter. Reducing power consumption in cic filter algorithm designs. Because of the popularity of this structure many authors also call the comb filter as cic filter. Filter the signal with a fir filter and coefficients 1 5 10 10 5 1. To see why the cic filter is of interest, first we examine its timedomain behavior, for d 5, shown in figure 3. I gotta wrap my head around to design cic compensation filter.
Previous efforts have focused on enhancing the performance of these filters by either improving their passband response 19,20 or stopband rejection capabilities 21. The most simple decimation filter is comb filter which does not require multipliers. Scopefir can design lowpass fir filters having a maximally flat passband. The cic core supports both interpolator and decima tor types. Cascaded integratorcomb cic filter introduction dspguru.
Therefore, cic is a suitable and economical filter architecture for hardware implementation, and is widely used in sample rate conversion designs such as digital down converters ddc and digital up converters duc. The design parameters for the filter are the frequency at which the peak or notch is desired, and either the 3db bandwidth or the filters qfactor. The cic interpolation filter increases the sampling rate by 32. Designing filters with the ad6620 application note an6620app1. Singlestage cic filter timedomain responses when d 5 view fullsized image. Scopefir is the premiere software tool for finite impulse response fir filter design. The design parameters for the filter are the frequency at which the peak or notch is desired, and either the 3db bandwidth or the filter s qfactor. Binary integers and overflow cascade integrator comb. A basic knowledge of dsp and digital filter design will help you understand the tradeoff between vari ous cic compensation filter design methods. Reducing power consumption in cic filter algorithm designs september 4, 2012 embedded staff a major design goal for cascaded integratorcomb cic filters, especially in conjunction with sample rate conversion, is to minimize their hardware power consumption by reducing data word width and reducing data clock rates wherever possible. The script uses the frequency sampling method to design a fir filter that has an inverse sinc frequency response. For this reason, many realworld filtering requirements cannot be met by a cic filter alone. To overcome the magnitude droop, a fir filter that has a magnitude response that is the inverse of the cic filter can be applied to achieve frequency response correction. This means that the cic filters frequency magnitude response is approximately equal to a sinc function centered at 0 hz.
The second subplot shows that the fir filter and cic filter provide nearly identical interpolation, when the correction gain equals the gain of the last section of the cic filter. An improved wideband cic filter design of software radio. Scopefir can design cic filters, which are widely used in hardwarebased multirate applications. Cic filters electrical engineering at new mexico tech. Implementation of optimized cascaded integrator comb filters. Using matlab program, the efficient five stage cic decimation filter is established. Bit width is addressed in more detail in a later section. Cic lters are much used in applications where one needs to change the sampling frequency in a big ratio, for instance for decimation reduction of the sampling rate.
The second fir interpolation filter is a compensation fir filter that increases the sampling rate by 2 and compensates for the distortion of the following cic filter. Design of cic filters for software radio system request pdf. These filters are used as decimation or interpolation filters and can be efficiently implemented without multipliers, utilizing only adders and subtractors. Implementation of optimized cascaded integrator comb. Hardware efficient fir compensation filter for delta sigma modulator analog to digital converters. The word lengths of the filter stages must be no increasing. Multiplierless wideband and narrowband cic compensator for. This block brings the filter design capabilities of the filterbuilder function to the simulink environment. Sep 04, 2012 reducing power consumption in cic filter algorithm designs september 4, 2012 embedded staff a major design goal for cascaded integratorcomb cic filters, especially in conjunction with sample rate conversion, is to minimize their hardware power consumption by reducing data word width and reducing data clock rates wherever possible. Overflow of integrator in cic filter there are many solution. The parameters of the design are the sinewave amplitudes expressed as powersoftwo and estimated in. An astounding digital filter design application rick lyons.
The transfer function of the cic filter can be written as. The initial model was designed and tested in simulink, a. The cic decimation filter with multichannel data support design example demonstrates how to use alteras cascaded integratorcomb cic filter megacore function to implement digital sample rate down conversion for multiple independent data sources. Understanding cascaded integratorcomb filters cic and. If a unitimpulsesequence, a unityvalued sample followed by many zerovalued samples, was applied to the comb stage, that stages output is. One efficient implementation of this filter is called cic cascadedintegratorcomb filter proposed by hogenauer hogenauer, 1981. To show how the cic decimation filter is constructed, the following figure presents a block diagram of the filter structure for a twosection cic decimation filter n 2. Cic filter is equivalent to a number of rectangular windows cascaded recursive filter form, and therefore has a more significant performance limitations. Magnitude response of a 1storder, d 8, decimating cic filter. A matlab script designing cic compensating filter is provided for your reference. With typical filter design software packages the user enters numerical values for the desired filter s parameters such as cutoff frequency, stopband attenuation, etc.
Cic filters are very useful in applications where one needs. Design cascaded integratorcomb cic filter simulink mathworks. The number of bits of the first filter stage must be greater than or equal to the quantity bmax. Designing digital down conversion systems using cic and. The shape of the filter response provides even fewer degrees of design freedom. Cic interpolation filter with multichannel data support for. It is combination of five stage integrator and comb stages. Moreover, given these specifications, by increasing the filter order, it is possible to obtain designs that more closely approximate an ideal filter. Using cic decimation filter with multichannel support. Pdf cic filter for sample rate conversion in software defined. The cic filter is used in both up sampling and down sampling applications. Request pdf design of cic filters for software radio system cascaded integrator comb cic filters are used to realize computationally efficient decimation, interpolation or sample rate. This scilab minitoolbox enables you to evaluate in terms of frequency response cic filters, to design what is called a compensation filter, and to simulate the cic filtering on real signals. The name of the core component to be instan tiated.
The ad6620 filter design software requires windows 95 or later 32bit operating. Cic compensator filter specification object matlab fdesign. With typical filter design software packages the user enters numerical values for the desired filters parameters such as cutoff frequency, stopband attenuation, etc. Nth order cascade integrated comb filter take n moving average filters in sequence with decimation at the end rearrange all integrators first, and comb filters. Design of five stage cic decimation filter for signal. The script uses the frequency sampling method to design a fir filter that has. A simple design for wideband compensation of a cascadedintegratorcomb cic decimation filter is presented.
In the cic filter design, the passband response and stopband rejection characteristics are managed by threeinteger parameters, which are number of stages, the differential delay and the number of bits in inputoutput registers. This paper presents multiplierless cic compensator for software defined radio sdr application. What is the benefits of a cic decimator compared to directly downsampling by 4 and. Its simple filter specification editor allows you to easily design simple. Cic filter cascaded integratorcomb cic filters, also known as hogenauer filters, are used to achieve arbitrary and large sample rate changes in digital systems. See the design and comments section for more information. In this tutorial, matthew donadio provides continued. The accumulator must have 17 or more bits to implement the 100tap boxcar filter as a cic filter. Hz1r 1zr1z1 n where, r and n are the decimation rate and order of the cic filter. Onchip implementation of cascaded integrated comb filters. Scopefir lets you import filters which have been designed with another application so you can analyze them using scopefirs powerful plotting and analysis capabilities, and to modify them using scopefirs powerful filter modification capabilities. In the classic paper, an economical class of digital filters for decimation and interpolation, hogenauer introduced an important class of digital filters called cascaded integratorcomb, or cic for short also sometimes called hogenauer filters.
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