CN100463366C - Digital medium frequency filtering method - Google Patents
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- CN100463366C CN100463366C CNB2006101554575A CN200610155457A CN100463366C CN 100463366 C CN100463366 C CN 100463366C CN B2006101554575 A CNB2006101554575 A CN B2006101554575A CN 200610155457 A CN200610155457 A CN 200610155457A CN 100463366 C CN100463366 C CN 100463366C
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Abstract
This invention relates to a digital IF filter method including: filtering analog IF signals with the input frequency of 140MHz and bandwidth smaller than 31.25MHz with a digital filter module orderly after being sampled by an A/D module, interpolating two times and with a low pass filter module 1 then to carry out low pass filter to the interpolated data, carrying out mixing operation with a mixing filter module to be interpolated two times and interpolated or two times by a high pass filter module then to carry out high pass filter to the data, carrying out signal mixing to the output signals passing through two times of interpolation and the low pass filter module 2 and 250 MHz local signals to be output by the A/D modile and low pass filter or band pass filter to get IF output with the central frequency of 160MHz.
Description
Technical field
The present invention relates to be fit to mobile communications network in the digital if technology field of RF direct amplifying station or Digital Television transponder, especially a kind of digital intermediate frequency filtering method.
Background technology
In today that mobile communication develops rapidly, the overlay area of which kind of radio communication all will produce weak signal area and blind area, and to some remote districts and the few blind area of number of users, adopt the repeater realize the signal covering be a kind of necessity and low cost solution.In 3G network today on the horizon, market has proposed new requirement to the repeater.As the WCDMA standard of one of mainstream standard of 3G, ripe application the in Europe also will become one of employing standard of China's 3G network.Because the WCDMA system can adopt single carrier or multiple radio frequency allocation plan, the intermediate-freuqncy signal bandwidth can change to 20MHz from 5MHz, this intermediate-frequency filter design to the WCDMA repeater has proposed stern challenge, adopt common analog filter on cost particularly flexibility can not meet the demands, need to adopt digitizing technique.Digital intermediate frequency filter bandwidht maximum among the at present existing relevant WCDMA has only about 15MHz, can only dispose 3 carrier waves at most like this, and IF-FRE is lower, and generally below 40MHz, this is unfavorable to designing and producing of back upconverter.
Summary of the invention
The objective of the invention is to solve the defective of above-mentioned prior art, and a kind of digital intermediate frequency filtering method is provided, this method adopts novel digital intermediate frequency filter frequencies allocation plan, also can be applicable in the Digital Television transponder.
Technical scheme of the present invention specifically is achieved in that this digital intermediate frequency filtering method, mainly comprises the steps:
1, be 140MHz with incoming frequency, and bandwidth is less than the analog if signal of 31.25MHz, by the A/D module samples, in the first Nyquist district, obtaining A/D conversion back digital intermediate frequency frequency F1 is the signal of 15Mhz, and the spectrum structure of the spectrum structure of this signal and 140MHz input signal is identical;
2, be that the signal of 15Mhz is made Filtering Processing by digital filtering module with IF-FRE F1, the output data rate of digital filtering module is 62.5MHz; The output signal of digital filtering module is made 2 times of interpolations earlier by 2 times of interpolations and low-pass filtering module one, promptly interleave one 0 Value Data in former data adjacent spots, the data rate after the interpolation is brought up to 125MHz, and then the data after the interpolation are made low-pass filtering;
3, earlier the output signal and the 20MHz local oscillator of 2 times of interpolations and low-pass filtering module one are done the mixing computing by the mixing and filtering module, choose centre frequency F2 in the signal after the mixing in the first Nyquist district and be 35MHz's and with the nonoverlapping signal of other frequency spectrum blocks, to this signal filtering, the data rate of mixing and filtering module is 125MHz again;
4, earlier the output signal of mixing and filtering module is made 2 times of interpolations by 2 times of interpolations and high-pass filtering module, be that former data adjacent spots interleaves one 0 Value Data, data rate after the interpolation is brought up to 250MHz, and then the data after the interpolation are done high-pass filtering, choose centre frequency F3 after the filtering in the first Nyquist district and be 90MHz's and not overlapping, but frequency spectrum becomes the signal of mirror with the frequency spectrum before the A/D with other frequency spectrum blocks;
5, earlier the output signal of 2 times of interpolations and high-pass filtering module is made 2 times of interpolations by 2 times of interpolations and low-pass filtering module two, be that former data adjacent spots interleaves one 0 Value Data, data rate after the interpolation is brought up to 500MHz, and then the data after the interpolation are made low-pass filtering;
6, the output signal and the 250MHz local oscillator of 2 times of interpolations and low-pass filtering two are carried out signal mixing by frequency mixing module, choose the signal that centre frequency is 160MHz in the first Nyquist district, and the signal spectrum structure of 160MHz is identical with the structure of A/D input signal, and this signal can obtain the intermediate frequency output that centre frequency is 160MHz behind the output of D/A module and low pass or bandpass filtering.
The sampling rate of A/D module of the present invention is 62.5MHz, and the signal bandwidth of sampling is greater than 155MHz.
Digital filtering module of the present invention can be according to concrete application requirements, realize different filtering characteristics, as can be configured to the digital filtering module bandwidth in the filtering of WCDMA digital intermediate frequency is 10MHz, but the WCDMA signal of gating two road adjacent carriers configuration, promptly every road WCDMA signal bandwidth 5MHz; And for example in the filtering of DVB-T digital intermediate frequency,, can be designed to 6MHz, 7MHz, three kinds of filtering bandwidths of 8MHz according to the difference of pattern.
The effect that the present invention is useful is: the present invention can realize the signal filtering to input intermediate frequency 140MHz, and can realize multiple channel filtering characteristic, and the output intermediate frequency can be risen to 160MHz, with the making of the back upconverter of being more convenient for.
● input intermediate-freuqncy signal, output intermediate-freuqncy signal adopt different frequencies, input intermediate frequency 140MHz, output intermediate frequency 160MHz;
● A/D, D/A adopt different specific sampling rates, and the sampling rate of A/D is 62.5MHz, and the sampling rate of D/A is 500MHz;
● adopted the digital mixing technology to realize the different conversion frequently of input, output frequency.
Description of drawings
Fig. 1 is a functional-block diagram of the present invention;
Fig. 2 is the spectrum diagram of 140MHz intermediate-freuqncy signal after the 62.5MHzA/D sampling among the present invention;
Fig. 3 be among the present invention in use the WCDMA repeater a kind of frequency characteristic schematic diagram of digital filter;
Fig. 4 is the output signal spectrum schematic diagram of 2 times of interpolations and low-pass filtering module one among the present invention;
Fig. 5 is a spectrum diagram after 2 times of interpolations and low-pass filtering module one and the mixing of 20MHz sinusoidal signal among the present invention;
Fig. 6 is the output spectrum schematic diagram of mixing and filtering module among the present invention;
Fig. 7 is the output spectrum schematic diagram of 2 times of interpolations and high-pass filtering module among the present invention;
Fig. 8 is the output spectrum schematic diagram of 2 times of interpolations and low-pass filtering module two among the present invention;
Fig. 9 is the output spectrum schematic diagram of frequency mixing module among the present invention;
Description of reference numerals: A/ D module 1,2,2 times of interpolations of digital filtering module and low-pass filtering module 1, mixing and filtering module 4, times interpolation and high-pass filtering module 5,2 times of interpolations and low-pass filtering module 26, frequency mixing module 7, D/A module 8,62.5MHz A/D sampling clock 9,20MHz local oscillator 10,250MHz local oscillator 11,500MHz D/A change over clock 12.
Embodiment
The invention will be described further below in conjunction with drawings and Examples:
This digital intermediate frequency filtering method mainly comprises the steps:
1, be 140MHz with incoming frequency, and bandwidth being less than the analog if signal of 31.25MHz, is A/D module 1 sampling of 62.5MHz by sampling rate, and the signal bandwidth of sampling is greater than 155MHz.In first Nyquist (Nyquist) district, obtaining A/D conversion back digital intermediate frequency frequency F1 is the signal of 15Mhz, and the spectrum structure of the spectrum structure of this signal and 140MHz input signal is identical.As shown in Figure 2, as long as the little and 31.25MHz of intermediate-freuqncy signal bandwidth, the frequency spectrum blocks of sampled signal mutually can aliasing.
Selecting for use of A/D module 1: mainly be the requirement that to consider sampling rate, bandwidth, A/D data bits.The sampling rate of A/D wants to reach the requirement of 62.5MHz, and the signal bandwidth that A/D can sample will satisfy the requirement greater than 155MHz, and the A/D data bits will consider to satisfy the S/N signal to noise ratio requirement of using.The AD5411 of TI company, the AD6644 of AD company etc. can satisfy the technical requirement of WCDMA repeater digital intermediate frequency.
2, be that the signal of 15Mhz is made Filtering Processing by digital filtering module 2 with IF-FRE F1, filtering characteristic requires to decide on the application scenario.The output data rate of digital filtering module 2 is 62.5MHz; As the application scenario to the WCDMA repeater, a kind of possible specific filtering template is illustrated in fig. 3 shown below, and the abscissa among Fig. 3 is represented frequency, and unit is MHz.The filter bandwidht of this pattern is 10MHz, but the every road of the WCDMA signal WCDMA signal bandwidth 5MHz of gating two road adjacent carriers configuration.The output signal of digital filtering module 2 is made 2 times of interpolations earlier by 2 times of interpolations and low-pass filtering module 1, promptly interleave one 0 Value Data in former data adjacent spots, data rate after the interpolation is brought up to 125MHz, and then the data after the interpolation are made low-pass filtering, after the filtering data spectrum structural representation as shown in Figure 4, the A place is shown low-frequency filter characteristics.For the sake of simplicity, the frequency spectrum blocks among Fig. 4 is not considered the influence of digital filtering module 2 characteristics.
3, earlier the output signal and the 20MHz local oscillator 10 of 2 times of interpolations and low-pass filtering module 1 are done the mixing computing by mixing and filtering module 4, can obtain spectrum structure schematic diagram as shown in Figure 5.20MHz local oscillator 10 can realize with the NCO digital vco in FPGA.Choose centre frequency F2 in the signal after the mixing in the first Nyquist district and be 35MHz's and with the nonoverlapping signal of other frequency spectrum blocks, signal spectrum schematic diagram after again this signal being leached with band pass filter as shown in Figure 6, the B place is shown band-pass filtering property, and the data rate of mixing and filtering module 4 is 125MHz.
4, earlier the output signal of mixing and filtering module 4 is made 2 times of interpolations by 2 times of interpolations and high-pass filtering module 5, be that former data adjacent spots interleaves one 0 Value Data, data rate after the interpolation is brought up to 250MHz, and then the data after the interpolation are done high-pass filtering, the data spectrum structural representation is illustrated in fig. 7 shown below after the filtering.Have in the first Nyquist district among Fig. 7 centre frequency F3 be 90MHz's and with the nonoverlapping signal of other frequency spectrum blocks, but the frequency spectrum before frequency spectrum and the A/D becomes mirror, the C place is shown the high-pass filtering characteristic.
5, earlier the output signal of 2 times of interpolations and high-pass filtering module 5 is made 2 times of interpolations by 2 times of interpolations and low-pass filtering module 26, be that former data adjacent spots interleaves one 0 Value Data, data rate after the interpolation is brought up to 500MHz, and then the data after the interpolation are made low-pass filtering, the data spectrum structural representation is illustrated in fig. 8 shown below after the filtering, and the D place is shown low-frequency filter characteristics.
6, the output signal and the 250MHz local oscillator 11 of 2 times of interpolations and low-pass filtering module 26 are carried out signal mixing by frequency mixing module 7, because the data transfer rate of 250MHz local oscillation signal is 500MHz, in fact the 250MHz signal can be considered+1-1+1-1 through sampled signals ... sequence, mixing computing are actually the output sequence and+1-1+1-1 of 2 times of interpolations and low-pass filtering 6 ... the phase multiplication of sequence.After the mixing computing, can obtain down output spectrum schematic diagram shown in Figure 9.By among Fig. 9 as can be known, having in the first Nyquist Nyquist district and having only centre frequency is the signal of 160MHz, and the signal spectrum structure of 160MHz is identical with the structure of A/D input signal.This signal can obtain the intermediate frequency output that centre frequency is 160MHz behind D/A output and low pass or bandpass filtering.
The operation principle explanation:
As shown in Figure 1,2,2 times of interpolations of digital filtering module and low-pass filtering module 1, mixing and filtering module 4,20MHz local oscillator 10 can realize that FPGA selects for use by FPGA (field programmable logic array) among Fig. 1: mainly be capacity and the speed of considering FPGA.Chips such as Cyclone II series EP2C35, the EP2C50 of Atera company can meet the demands, 2,2 times of interpolations of digital filtering module among the FPGA and low-pass filtering module 1, mixing and filtering module 4,20MHz local oscillator 10 are to generate by FPGA is downloaded specific configurator, configurator is by eda tool software, adopts VHDL or other programming languages to generate.2 times of interpolations and 5,2 times of interpolations of high-pass filtering module and low-pass filtering 6, mixing 7, D/A8,250MHz local oscillator 11 can be realized by the D/A of band interpolation functions, the D/A chip of band interpolation functions is selected for use: mainly be whether consideration speed and function meet the demands, the speed of the DAC5687 chip of TI company and function can satisfy the enforcement requirement of this patent fully, and the concrete function of the D/A chip of band interpolation functions is to load specific configuration data by single-chip microcomputer register in D/A to produce.62.5MHz A/D sampling clock 9 is provided by outer clock circuit.500MHz D/A change over clock 12 can be provided by outer clock circuit, and also available D/A clock internal circuit by the band interpolation functions produces.9, the frequency of Unit 10,11,12 is by producing based on same reference frequency source, thereby is synchronized with same reference frequency source.F among the figure
S1, F
S2, F
S3, F
S4Represent the data sampling speed of each signal node, 15MHz, 35MHz, 95MHz, 160MHz represent the centre frequency of each node signal.
Relevant frequency relation in the block diagram:
● analog if signal incoming frequency: Fin=140MHz
● A/D conversion back numeric field IF-FRE: F1=Fin-2Fs1=15MHz
● the frequency in the Digital IF Processing unit after the mixing: F2=F1+Fo=35MHz Fo is the 20MHz local frequency
● frequency: F3=2Fs1-F2=90MHz after 2 times of interpolations and the high-pass filtering in D/A band interpolation functions
● the frequency in D/A band interpolation functions after 4 times of interpolation filterings and the mixing: F4=4Fs1-F3=160MHz
● DAC5687 output frequency: Fout=F4=160MHz
In addition to the implementation, the present invention can also have other execution modes.All employings are equal to the technical scheme of replacement or equivalent transformation formation, all drop on the protection range of requirement of the present invention.
Claims (2)
1. digital intermediate frequency filtering method, it is characterized in that: this method mainly comprises the steps:
1.1), be 140MHz with incoming frequency, and bandwidth is less than the analog if signal of 31.25MHz, sample by A/D module (1), in the first Nyquist district, obtaining A/D conversion back digital intermediate frequency frequency F1 is the signal of 15Mhz, and the spectrum structure of the spectrum structure of this signal and 140MHz input signal is identical;
1.2), be that the signal of 15Mhz is made Filtering Processing by digital filtering module (2) with IF-FRE F1, the output data rate of digital filtering module (2) is 62.5MHz; The output signal of digital filtering module (2) is made 2 times of interpolations earlier by 2 times of interpolations and low-pass filtering module one (3), promptly interleave one 0 Value Data in former data adjacent spots, data rate after the interpolation is brought up to 125MHz, and then the data after the interpolation are made low-pass filtering;
1.3), earlier the output signal and the 20MHz local oscillator (10) of 2 times of interpolations and low-pass filtering module one (3) are done the mixing computing by mixing and filtering module (4), choose centre frequency F2 in the signal after the mixing in the first Nyquist district and be 35MHz's and with the nonoverlapping signal of other frequency spectrum blocks, to this signal filtering, the data rate of mixing and filtering module (4) is 125MHz again;
1.4), earlier the output signal of mixing and filtering module (4) is made 2 times of interpolations by 2 times of interpolations and high-pass filtering module (5), be that former data adjacent spots interleaves one 0 Value Data, data rate after the interpolation is brought up to 250MHz, and then the data after the interpolation are done high-pass filtering, choose centre frequency F3 after the filtering in the first Nyquist district and be 90MHz's and not overlapping with other frequency spectrum blocks;
1.5), earlier the output signal of 2 times of interpolations and high-pass filtering module (5) is made 2 times of interpolations by 2 times of interpolations and low-pass filtering module two (6), be that former data adjacent spots interleaves one 0 Value Data, data rate after the interpolation is brought up to 500MHz, and then the data after the interpolation are made low-pass filtering;
1.6), the output signal and the 250MHz local oscillator (11) of 2 times of interpolations and low-pass filtering module two (6) are carried out signal mixing by frequency mixing module (7), choose the signal that centre frequency is 160MHz in the first Nyquist district, and the signal spectrum structure of 160MHz is identical with the structure of A/D input signal, and this signal can obtain the intermediate frequency output that centre frequency is 160MHz behind (8) output of D/A module and low pass or bandpass filtering.
2. digital intermediate frequency filtering method according to claim 1 is characterized in that: the sampling rate of described A/D module (1) is 62.5MHz, and the signal bandwidth of sampling is greater than 155MHz.
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| CN101997555A (en) * | 2010-09-09 | 2011-03-30 | 天津七一二通信广播有限公司 | Method for compatible processing of various bandwidth signals by fixed-bandwidth intermediate-frequency filter circuit |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US6973138B1 (en) * | 2000-01-26 | 2005-12-06 | Pmc-Sierra, Inc. | Advanced adaptive pre-distortion in a radio frequency transmitter |
| WO2006044607A1 (en) * | 2004-10-13 | 2006-04-27 | Analog Devices, Inc. | Filters for communication systems |
| CN1804642A (en) * | 2006-01-23 | 2006-07-19 | 天津市德力电子仪器有限公司 | Middle-frequency completely digital frequency spectrum |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6973138B1 (en) * | 2000-01-26 | 2005-12-06 | Pmc-Sierra, Inc. | Advanced adaptive pre-distortion in a radio frequency transmitter |
| WO2006044607A1 (en) * | 2004-10-13 | 2006-04-27 | Analog Devices, Inc. | Filters for communication systems |
| CN1804642A (en) * | 2006-01-23 | 2006-07-19 | 天津市德力电子仪器有限公司 | Middle-frequency completely digital frequency spectrum |
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Effective date of registration: 20090220 Address after: No. 581, Torch Road, Zhejiang, Hangzhou Province: 310053 Co-patentee after: Hangzhou Electronic Science and Technology Univ Patentee after: Three dimensional communication Limited by Share Ltd Address before: No. 92 Huaxing Road, Zhejiang, Hangzhou Province: 310012 Co-patentee before: Hangzhou Electronic Science and Technology Univ Patentee before: Zhejiang three dimensional communications Limited by Share Ltd |
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