CN106571790A - CIC filter passband flatness compensation filter design method - Google Patents

CIC filter passband flatness compensation filter design method Download PDF

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Publication number
CN106571790A
CN106571790A CN201610952734.9A CN201610952734A CN106571790A CN 106571790 A CN106571790 A CN 106571790A CN 201610952734 A CN201610952734 A CN 201610952734A CN 106571790 A CN106571790 A CN 106571790A
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filter
cic
setting
ripple
compensating
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CN201610952734.9A
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CN106571790B (en
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刘同领
张永晓
周三文
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Aerospace Long March Launch Vehicle Technology Co Ltd
Beijing Institute of Telemetry Technology
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Aerospace Long March Launch Vehicle Technology Co Ltd
Beijing Institute of Telemetry Technology
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H17/02—Frequency selective networks
    • H03H17/0219—Compensation of undesirable effects, e.g. quantisation noise, overflow
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H17/00—Networks using digital techniques
    • H03H17/02—Frequency selective networks
    • H03H17/06—Non-recursive filters
    • H03H17/0621—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing
    • H03H17/0635—Non-recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies
    • H03H17/0671—Cascaded integrator-comb [CIC] filters

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Mathematical Physics (AREA)
  • Filters That Use Time-Delay Elements (AREA)

Abstract

The invention provides a CIC filter passband flatness compensation filter design method. The method comprises the steps that 1 the time domain impulse response function h(t)=Sa(2pif0t) of an ideal filter is generated; 2 sampling discretization is carried out on h(t) to acquire a discrete impulse response function h(n); 3 h(n) is intercepted and weighted to acquire a truncated response function hc(n); and 4 the 6D+1-th value in the truncated response function hc(n) is acquired, and is used as the filter coefficient of a 6D+1 order compensation filter, and the compensation filter is used to filter the output signal of a CIC filter. According to the method, the designed compensation filter can improve the passband flatness of the CIC filter; stopband attenuation is increased; and the method is simple and easy to implement in engineering.

Description

A kind of cic filter pass-band flatness compensating filter method for designing
Technical field
The present invention relates to digital signal processing technique field, more particularly to a kind of cic filter pass-band flatness compensation filter Ripple device method for designing.
Background technology
The symbol rate of Modem radio digital communication system is mostly variable, and the modulated terminal and demodulating end of baseband communication equipment are led to Often need to carry out the sampling rate conversion of signal to economize on resources, reduce power consumption.For the variable situation of signal code rate, Chang Huishe The signal sampling rate mapped structure of meter multi-stage cascade, multistage Variable sampling process Variable sampling generally few with amount of calculation, being easily achieved Wave filter is cascaded, such as cic filter, half-band filter etc..Cic filter is used at the multi-sampling rate signal of integral multiple Reason, half-band FIR filter are used for 2NMulti-sampling rate signal again is processed.
Cic filter pass band damping is fast, Sidelobe Suppression is less, frequency response characteristic limits which the shortcomings of changing more difficult Application in passband and Stopband Performance require higher sampling rate conversion system.In order to reduce passband distortion, increase CIC filtering The suitability of device, needs are improved to traditional cic filter, improve its passband, Stopband Performance.
Existing cic filter compensation method has：ISOP (interpolated second-order polynomials) compensation method, and it is improved Sharpened cic filters etc..Wherein, ISOP compensation methodes have also damaged Stopband Performance while band-pass behavior is improved Lose, and improved Sharpened cic filters method for designing realizes underaction, algorithm amount of calculation is larger.
The content of the invention
It is an object of the invention to overcome the shortcoming of prior art, there is provided a kind of cic filter pass-band flatness compensation Filter design method, the compensating filter that the method design is obtained can improve the pass-band flatness of cic filter, and can increase Plus stopband attenuation, implementation method is simple, it is easy to Project Realization.
The above-mentioned purpose of the present invention is realized by below scheme：
A kind of cic filter pass-band flatness compensating filter method for designing, comprises the following steps：
(1) time domain impulse receptance function h (t)=Sa (2 π f of ideal filter, are generated0T), wherein, f0For the reason of setting Think filter cutoff frequency；
(2) sampling discretization is carried out to time domain impulse receptance function h (t), discrete impulse Response Function h (n) is obtained, its In, sample frequency fs=2f0D；D is the cic filter signal sampling rate conversion multiple of setting；
(3), carry out intercepting to obtain blocking receptance function h to h (n)c(n)：
Wherein, α is the first secondary lobe waveform weight coefficient of setting；β is the second secondary lobe waveform weight coefficient of setting；
(4) receptance function h will be blocked,c6D+1 value in (n), as the filter factor of 6D+1 rank compensating filters； Then process is filtered to the output signal of cic filter using the compensating filter.
Above-mentioned cic filter pass-band flatness compensating filter method for designing, in step (3), adopts with the following method Determine the value of the first secondary lobe waveform weight coefficient α and the second secondary lobe waveform weight coefficient β：
A (), to set the span of α as the span of 0～10, β be 0～10；
B (), α, β value in the setting span, and is compensated filter factor hc(n)；
(c), to hcN () carries out FFT, obtain frequency response Hc(w)；
(d), compound frequency response function H (the w)=H for calculating cic filter and compensating filterc(w)HCIC(w)；Its In, HCICW () is the cic filter frequency response function of setting；
E (), the passband ripple to H (w) and stopband attenuation amount are calculated, and make the following judgment：
If the passband ripple of H (w) is less than or equal to setting ripple thresholding, and stopband attenuation amount is more than or equal to setting resistance Band attenuation threshold, then judge that the value of α, β meets and require；If the passband ripple of H (w) is more than setting ripple thresholding, or stopband Attenuation is less than setting stopband attenuation thresholding, then return to step (b).
Description of the drawings
Fig. 1 is the frequency response letter curve of cic filter in embodiment；
Fig. 2 blocks receptance function h for what is obtained in embodimentcThe time domain waveform of (n)；
Fig. 3 is frequency domain response comparing result of the cic filter before and after compensation in embodiment.
Specific embodiment
The present invention is described in further detail with instantiation below in conjunction with the accompanying drawings：
The compensating filter of present invention design, for compensating filtering to the output signal of cic filter, so as to improve The passband ripple and attenuation outside a channel performance of cic filter.Implement process as follows：
(1) time domain impulse receptance function h (t)=Sa (2 π f of ideal filter, are generated0T), i.e.,：Wherein, f0For the ideal filter cut-off frequency of setting, the setup parameter is only used for producing preferable punching Receptance function is hit, but does not affect follow-up compensation filter coefficient results.
(2) sampling discretization is carried out to time domain impulse receptance function h (t), discrete impulse Response Function h (n) is obtained, its In, sample frequency fs=2f0D, i.e.,D is the cic filter signal sampling rate conversion multiple of setting；
(3), carry out intercepting to obtain blocking receptance function h to h (n)c(n)：
I.e.：
Wherein, α is the first secondary lobe waveform weight coefficient of setting；β is the second secondary lobe waveform weight coefficient of setting.More than Intercept operation be equivalent to rectangular window intercepting carried out to preferable discrete impulse Response Function h (n), the adding window is intercepted and can produce Ji Buss phenomenon, i.e., can make the passband and stopband of ideal filter occur fluctuating up and down, and the present invention is exactly using this ripple effect Realize the compensation to cic filter.Because the logical band attenuation of cic filter is too fast, and blocks receptance function hcN () can Yin Jibu This phenomenon occurs fluctuating in passband upwards, and this fluctuation can be compensated to the decay in cic filter passband.
(4) receptance function h will be blocked,c6D+1 value in (n), as the filter factor of 6D+1 rank compensating filters； Then process is filtered to the output signal of cic filter using the compensating filter.
When concrete engineering is realized, the value meeting of the first secondary lobe waveform weight coefficient α and the second secondary lobe waveform weight coefficient β The compensation effect of compensating filter, therefore the present invention is affected to adopt The value of two secondary lobe waveform weight coefficient β：
A (), to set the span of α as the span of 0～10, β be 0～10；
B (), α, β value in the setting span, and is compensated filter factor hc(n)；
(c), to hcN () carries out FFT, obtain frequency response Hc(w)；
(d), compound frequency response function H (the w)=H for calculating cic filter and compensating filterc(w)HCIC(w)；Its In, HCICW () is the cic filter frequency response function of setting；
E (), the passband ripple to H (w) and stopband attenuation amount are calculated, and make the following judgment：
If the passband ripple of H (w) is less than or equal to setting ripple thresholding, and stopband attenuation amount is more than or equal to setting resistance Band attenuation threshold, then judge that the value of α, β meets and require；If the passband ripple of H (w) is more than setting ripple thresholding, or stopband Attenuation is less than setting stopband attenuation thresholding, then return to step (b).
Embodiment：
In the present embodiment, cic filter signal sampling rate conversion multiple D=5, and the frequency domain response of the cic filter Function HCICW () is as shown in figure 1, the band attenuation of the frequency response function is very fast, therefore is obtained using method of the present invention design Compensating filter is compensated to the cic filter.
Method for designing of the invention, firstly generates ideal filter time domain impulse receptance function h (t), then to h T () carries out discrete sampling and adding window is intercepted, and only retains two secondary lobes, and set the first secondary lobe waveform weight coefficient α after intercepting =3.02, the second secondary lobe waveform weight coefficient β=1.Obtain as shown in Figure 2 blocking receptance function hc(n), wherein：
Using hcN () compensates filtering to the output signal of cic filter as time-domain taps coefficient.The CIC is filtered As shown in figure 3, wherein, it is the compound of cic filter and compensating filter that solid line is corresponding to frequency domain response of the device before and after compensation Frequency domain response H (w)=Hc(w)HCIC(w)。
From figure 3, it can be seen that after compensating to cic filter using the compensating filter of the present invention, CIC can be improved Waveform performance in the passband of wave filter, and improve attenuation outside a channel.
The above, only one specific embodiment of the present invention, but protection scope of the present invention is not limited thereto, and appoints What those familiar with the art the invention discloses technical scope in, the change or replacement that can be readily occurred in, all Should be included within the scope of the present invention.
The content not being described in detail in description of the invention belongs to the known technology of professional and technical personnel in the field.

Claims (2)

1. a kind of cic filter pass-band flatness compensating filter method for designing, it is characterised in that comprise the following steps：
(1) time domain impulse receptance function h (t)=Sa (2 π f of ideal filter, are generated0T), wherein, f0For the preferable filter of setting Ripple device cut-off frequency；
(2) sampling discretization is carried out to time domain impulse receptance function h (t), discrete impulse Response Function h (n) is obtained, wherein, adopt Sample frequency fs=2f0D；D is the cic filter signal sampling rate conversion multiple of setting；
(3), carry out intercepting to obtain blocking receptance function h to h (n)c(n)：
h c ( n ) = h ( n ) , - D &le; n &le; D &alpha; &CenterDot; h ( n ) , D < | n | &le; 2 D &beta; &CenterDot; h ( n ) , 2 D < | n | &le; 3 D
Wherein, α is the first secondary lobe waveform weight coefficient of setting；β is the second secondary lobe waveform weight coefficient of setting；
(4) receptance function h will be blocked,c6D+1 value in (n), as the filter factor of 6D+1 rank compensating filters；Then Process is filtered to the output signal of cic filter using the compensating filter.
2. a kind of cic filter pass-band flatness compensating filter method for designing according to claim 1, its feature exist In：In step (3), adopt and determine the first secondary lobe waveform weight coefficient α's and the second secondary lobe waveform weight coefficient β with the following method Value：
A (), to set the span of α as the span of 0～10, β be 0～10；
B (), α, β value in the setting span, and is compensated filter factor hc(n)；
(c), to hcN () carries out FFT, obtain frequency response Hc(w)；
(d), compound frequency response function H (the w)=H for calculating cic filter and compensating filterc(w)HCIC(w)；Wherein, HCIC W () is the cic filter frequency response function of setting；
E (), the passband ripple to H (w) and stopband attenuation amount are calculated, and make the following judgment：
If the passband ripple of H (w) declines more than or equal to setting stopband less than or equal to setting ripple thresholding, and stopband attenuation amount Subtract thresholding, then judge that the value of α, β meets and require；If the passband ripple of H (w) is more than setting ripple thresholding, or stopband attenuation Amount is less than setting stopband attenuation thresholding, then return to step (b).
CN201610952734.9A 2016-11-02 2016-11-02 A kind of cic filter pass-band flatness compensating filter design method Active CN106571790B (en)

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Publication number Priority date Publication date Assignee Title
CN112818526A (en) * 2021-01-20 2021-05-18 桂林电子科技大学 Distributed design method of non-uniform graph filter bank

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CN101510756A (en) * 2009-03-06 2009-08-19 山东大学 Digital signal down variable frequency processing system based on MIMO real time test platform
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US20050280564A1 (en) * 2004-06-22 2005-12-22 Samsung Thales Co., Ltd. Digital sampling rate converter for compensating for drop of in-band signal
KR100824299B1 (en) * 2006-12-26 2008-04-23 에스케이텔레시스 주식회사 Interface system for wibro network and filter embodying method for roll off compensation
CN101510756A (en) * 2009-03-06 2009-08-19 山东大学 Digital signal down variable frequency processing system based on MIMO real time test platform
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Publication number Priority date Publication date Assignee Title
CN112818526A (en) * 2021-01-20 2021-05-18 桂林电子科技大学 Distributed design method of non-uniform graph filter bank
CN112818526B (en) * 2021-01-20 2022-09-30 桂林电子科技大学 Distributed design method of non-uniform graph filter bank

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