CN102045283A - FSK (Frequency Shift Keying) demodulator - Google Patents
FSK (Frequency Shift Keying) demodulator Download PDFInfo
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- CN102045283A CN102045283A CN2009102016056A CN200910201605A CN102045283A CN 102045283 A CN102045283 A CN 102045283A CN 2009102016056 A CN2009102016056 A CN 2009102016056A CN 200910201605 A CN200910201605 A CN 200910201605A CN 102045283 A CN102045283 A CN 102045283A
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Abstract
The invention discloses an FSK (Frequency Shift Keying) demodulator which comprises a digital to analog converter, a lower frequency converter, two paths of radio-frequency filters and an adaptive lookup table, wherein the digital to analog converter is used for converting a radio-frequency front-end signal into a digital signal; the lower frequency converter is connected with the digital to analog converter and used for generating two paths of orthogonal mixing signals by a local oscillator and multiplying the two paths of orthogonal mixing signals by an input signal to obtain two paths of zero intermediate frequency radio-frequency signals; the two paths of radio-frequency filters are connected with the lower frequency converter and used for filtering the zero intermediate frequency radio-frequency signals and filtering out out-of-band transformation noise and high-frequency product components in the mixed signals simultaneously; and the adaptive lookup table is connected with the two paths of radio-frequency filters and used for analyzing the amplitudes of two paths of input signals; and if the amplitude of any one path of signals exceeds the addressing space of the table, adaptive amplitude decrease is carried out, and then the table is looked up according to the amplitudes of the two paths of signals to output angles corresponding to vectors. The invention provides the FSK demodulator with lower cost, which can effectively reduce the area and the power consumption of a chip.
Description
Technical field
The present invention relates to a kind of communication equipment, be specifically related to the demodulator in a kind of wireless communication system.
Background technology
At present, FSK (Frequency-shift keying) FSK demodulator has a variety of methods to realize, the fsk demodulator of earliest period adopts the phase-locked loop pll mode to realize, comprises analog PLL or digital PLL.This class demodulator is directly handled signal at intermediate frequency, and many shortcomings are arranged, and such as the application that is not suitable for high data rate, power consumption height and area are big.
Fsk demodulator progressively used the mode of Digital Signal Processing to realize afterwards, usually after single-channel RF is signal digitalized, use two band pass filters, the modulating frequency of filter center frequency corresponding symbol 0 of difference and symbol 1, such two band pass filters need use IIR (wireless impulse response) filter of high-order, realize the bigger multiplier of space required.
Up-to-date mostly use amplitude of fsk demodulator is to phase converter, this conversion or realize by a formula that needs multiplication, use CORDIC (CoordinateRotation Digital Computer) CORDIC rotation mode, because this method needs the two-way input, so need two digital to analog converter ADC usually, also the someone uses a time-multiplexed method of digital to analog converter ADC to save area, but require digital to analog converter ADC operating frequency to double, use for modern high speed like this, be that power consumption is excessive, or be that cost is too high.
The lower fsk demodulator of a kind of cost is arranged, use zero crossing to detect, this class demodulator only is fit to the very application of low rate, and performance is well below theoretical demodulation performance.
As shown in Figure 1, at present, existing product comprises two-way digital to analog converter (digital to analog converter ADC), two-way radio-frequency signal filters, a vectorial circulator, a difference engine, a baseband signal filter.
A subject matter of existing product is to need two-way radiofrequency signal input I/Q, and this just needs two digital to analog converter ADC that are operated in the high frequency sample frequency.Usually high frequency digital to analog converter ADC area and power consumption are all very big, cause the cost of whole demodulator very high.
The another one problem of existing product is for fear of the influence to final demodulation result of digital to analog converter ADC and front end low-frequency noise, the radio-frequency filter input signal is not baseband signal usually, but certain intermediate frequency is arranged, so just require the radio-frequency filter bandwidth of operation wideer, operating frequency is higher, the result causes the demodulator power consumption very big, and cost is very high.
The problem that also has of existing product is to need vectorial circulator to calculate angle according to the amplitude of two-way input vector signal, and this uses cordic algorithm to realize usually.Although computational methods that cordic algorithm is effectively simple, and reduced demand to chip area, still need a plurality of plus-minuss unit and control unit.
The output accuracy that to also have a problem be vectorial circulator of existing product is relevant with the amplitude of input signal, and is less than normal when input signal amplitude, may cause a lot of cycles of circulator in idle running, and effective revolution reduces.All radio-frequency filter output can be amplified in most of like this design, to allow vectorial circulator also can satisfy performance requirement under the minimum signal amplitude, this can cause the raising of chip cost.
Summary of the invention
Technical problem to be solved by this invention provides a kind of fsk demodulator, and it can effectively reduce chip area and power consumption, reduces cost.
In order to solve above technical problem, the invention provides a kind of fsk demodulator; Comprise:
A digital to analog converter, digital to analog converter is converted into digital signal with the radio-frequency front-end signal;
Low-converter, it is connected with digital to analog converter, uses a local oscillator to produce quadrature two-way mixed frequency signal, obtains two-way zero intermediate frequency radiofrequency signal after multiplying each other with input signal respectively;
The two-way radio-frequency filter, it is connected with low-converter, and the zero intermediate frequency radiofrequency signal is carried out filtering, filters out the outer noise that transforms of band, simultaneously the high frequency product component in the signal after the mixing is filtered out;
The self adaptation look-up table, it is connected with the two-way radio-frequency filter, and the amplitude of two paths of signals of input is analyzed, if any one tunnel signal amplitude exceeds the addressing space of table, then carry out the amplitude self adaptation and dwindle, table look-up the angle of output vector correspondence then according to the size of two paths of signals.
Beneficial effect of the present invention is: a kind of lower-cost fsk demodulator is provided, and this demodulator need not two-way digital to analog converter ADC, can effectively reduce chip area and power consumption.And the present invention down-converts the signals to base band, to reduce the requirement to radio-frequency filter, reduces the power consumption of radio-frequency filter and the chip area that takies.The present invention replaces with self adaptation look-up table cheaply with vectorial circulator.Look-up table has reduced the calculating power consumption of system owing to need not rotation, has save the area of computing unit, and need not to amplify in order to adapt to small-signal front end output.Simultaneously the input vector amplitude is carried out self adaptation according to the addressing space size of look-up table and dwindle, even very big also need not of front end signal enlarges look-up table like this.
Description of drawings
Below in conjunction with the drawings and specific embodiments the present invention is described in further detail.
Fig. 1 is existing fsk demodulator schematic diagram;
Fig. 2 is the described fsk demodulator schematic diagram of the embodiment of the invention.
Embodiment
The invention provides a kind of lower-cost fsk demodulator, this demodulator need not two-way digital to analog converter ADC, can effectively reduce chip area and power consumption.And the present invention down-converts the signals to base band, to reduce the requirement to radio-frequency filter, reduces the power consumption of radio-frequency filter and the chip area that takies.The present invention replaces with self adaptation look-up table cheaply with vectorial circulator.Look-up table has reduced the calculating power consumption of system owing to need not rotation, has save the area of computing unit, and need not to amplify in order to adapt to small-signal front end output.Simultaneously the input vector amplitude is carried out self adaptation according to the addressing space size of look-up table and dwindle, even very big also need not of front end signal enlarges look-up table like this.
As shown in Figure 2, critical piece of the present invention comprises a digital to analog converter ADC, a low-converter, two radio-frequency filters, a self adaptation look-up table, a difference engine and a baseband signal filter.
Digital to analog converter ADC is converted into digital signal with the radio-frequency front-end signal, and digital to analog converter ADC input signal has been finished neighboring trace filtering and mirror image inhibition usually.
Low-converter uses a local oscillator to produce quadrature two-way mixed frequency signal, obtains two-way zero intermediate frequency radiofrequency signal after multiplying each other with input signal respectively.
Radio-frequency filter carries out filtering to the zero intermediate frequency radiofrequency signal, not only filters out the outer noise that transforms of band, also simultaneously the high frequency product component in the signal after the mixing is filtered out.
The self adaptation look-up table is at first analyzed the amplitude of two paths of signals of input, if any one tunnel signal amplitude exceeds the addressing space of table, then carries out the amplitude self adaptation and dwindles.Table look-up the angle of output vector correspondence then according to the size of two paths of signals.
Difference engine carries out calculus of differences to input signal, transfers angle to frequency.Follow-up baseband signal filter is exported difference engine and is carried out smothing filtering, obtains final demodulation output.
Digital to analog converter ADC is input as the radio-frequency front-end signal among the present invention, and the output of digital to analog converter ADC enters low-converter.
The quadrature two-way output of low-converter is connected respectively to two radio-frequency filters.The latter's output is connected to the input of self application look-up table.
The output of self adaptation look-up table is connected to difference engine, and the baseband signal filter is given in the latter's output.
The baseband signal filter is finally exported demodulation result.
Digital to analog converter ADC is converted into digital signal with the fsk modulated signal of radio-frequency front-end, and the fsk modulated signal of this moment has an intermediate frequency, IF-FRE is designed to 1/8 of digital to analog converter ADC sample rate here.
Low-converter produces the local oscillation signal of two-way quadrature, uses the two-way local oscillation signal to multiply each other with input signal respectively then, obtains two-way zero intermediate frequency modulation signal.Because middle IF-FRE is 1/8 of sample rate, be that 8 fixing sequence just can be described so local oscillation signal only uses one-period, the one-period sequence of the local oscillation signal correspondence of two-way quadrature is as follows:
I road local oscillator: [0 0.7071 1 0.7071 0-0.7071-1-0.7071]
Q road local oscillator: [1 0.7071 0-0.7071-1-0.7071 0 0.7071]
Obviously, when local oscillation signal and input signal multiply each other, wherein 0,1 ,-1 be exactly simple the selection and negate, and X*0.707 can use X/2+X/4+X/16 be similar to realizations, the latter simply is shifted and addition, need not multiplication.
After obtaining zero intermediate frequency signals, radio-frequency filter carries out filter to this signal, and in order to reduce cost, the mode of 1 of filter employing or the cascade of a plurality of complete 1 coefficient FIRs (finite impulse response) filter realizes.At first complete 1 coefficient filter need not multiplication, the realization cost is low, and the mode of cascade makes filter be easy to configuration, for different application, can be different cascade systems with filter configuration, be fit to the reasonable situation of communication environment such as single-stage, and the multistage communication requirement that is fit to farther distance.
The self adaptation look-up table at first carries out the amplitude self adaptation to filtered signal.If wherein the amplitude of one road signal exceeds the addressing space of look-up table, then carry out amplitude compression, compression factor is always 2 integral multiple, only just can realize by displacement to guarantee compression.Value such as I, Q two paths of signals is respectively 30 and 14, and look-up table addressing maximum is 15, then with 2 times of I, Q signal amplitude compression to 15 and 7.
Signal after the self adaptation amplitude is handled is used for look-up table is carried out addressing, and purpose is to realize the conversion of orthogonal signalling amplitude to corresponding angle, because angle has simple corresponding relation at four quadrants, so look-up table only needs a quadrant just can.Such as the whole size of look-up table is 16X16, and angle uses 8 bit digital to transform.Final angle will carry out reprocessing according to the symbol of look-up table output and signal.
Follow-up difference engine is exactly simple subtraction.And the baseband signal filter uses complete 1 coefficient FIR filter cascade fully as the design of radio-frequency filter, to realize the performance of expectation with minimum cost, allows design can be disposed at different application demands easily simultaneously.
The present invention is not limited to execution mode discussed above.More than the description of embodiment is intended in order to describe and illustrate the technical scheme that the present invention relates to.Based on the conspicuous conversion of the present invention enlightenment or substitute and also should be considered to fall into protection scope of the present invention.Above embodiment is used for disclosing best implementation method of the present invention, so that those of ordinary skill in the art can use numerous embodiments of the present invention and multiple alternative reaches purpose of the present invention.
Claims (10)
1. fsk demodulator; It is characterized in that, comprising:
A digital to analog converter, digital to analog converter is converted into digital signal with the radio-frequency front-end signal;
Low-converter, it is connected with digital to analog converter, uses a local oscillator to produce quadrature two-way mixed frequency signal, obtains two-way zero intermediate frequency radiofrequency signal after multiplying each other with input signal respectively;
The two-way radio-frequency filter, it is connected with low-converter, and the zero intermediate frequency radiofrequency signal is carried out filtering, filters out the outer noise that transforms of band, simultaneously the high frequency product component in the signal after the mixing is filtered out;
The self adaptation look-up table, it is connected with the two-way radio-frequency filter, and the amplitude of two paths of signals of input is analyzed, if any one tunnel signal amplitude exceeds the addressing space of table, then carry out the amplitude self adaptation and dwindle, table look-up the angle of output vector correspondence then according to the size of two paths of signals.
2. fsk demodulator as claimed in claim 1; It is characterized in that, also comprise: difference engine, it is connected with the self adaptation look-up table, and input signal is carried out calculus of differences, transfers angle to frequency.
3. fsk demodulator as claimed in claim 2; It is characterized in that, also comprise: the baseband signal filter, it is connected with difference engine, and smothing filtering is carried out in output to difference engine, obtains final demodulation output.
4. fsk demodulator as claimed in claim 3; It is characterized in that described difference engine carries out subtraction; The baseband signal filter forms for one or more complete 1 coefficient finite impulse response FIR filter single-stage or multi-stage cascade.
5. fsk demodulator as claimed in claim 1; It is characterized in that described digital to analog converter ADC is converted into digital signal with the fsk modulated signal of radio-frequency front-end, the fsk modulated signal of this moment has an intermediate frequency, and IF-FRE is 1/8 of a digital to analog converter ADC sample rate.
6. fsk demodulator as claimed in claim 5; It is characterized in that the orthogonal local oscillation signal that local oscillator produces is that one-period is 8 fixing sequence.
7. fsk demodulator as claimed in claim 1; It is characterized in that the described radio-frequency filter that the zero intermediate frequency radiofrequency signal is carried out filtering forms for one or more complete 1 coefficient finite impulse response FIR filter cascade.
8. fsk demodulator as claimed in claim 7; It is characterized in that described radio-frequency filter is single-stage or multi-stage cascade.
9. fsk demodulator as claimed in claim 1; It is characterized in that described self adaptation look-up table at first carries out the amplitude self adaptation to filtered signal, if the amplitude of one road signal addressing space that exceeds look-up table wherein then carries out amplitude compression, compression factor is always 2 integral multiple.
10. fsk demodulator as claimed in claim 1; It is characterized in that the signal after described self adaptation amplitude is handled is used for look-up table is carried out addressing, realize the conversion of orthogonal signalling amplitude to corresponding angle, look-up table only need be looked into a quadrant, and final angle is handled according to the symbol of look-up table output and signal.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014029142A1 (en) * | 2012-08-22 | 2014-02-27 | 天津大学 | Radio-frequency front end in high and medium frequency superheterodyne+zero intermediate frequency structure |
| CN108023846A (en) * | 2016-11-04 | 2018-05-11 | 意法设计与应用股份有限公司 | Detect method, circuit, equipment and the computer program product of fsk modulated signal |
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| CN1081551A (en) * | 1992-05-06 | 1994-02-02 | 日本电气株式会社 | Fsk receiver |
| US6304140B1 (en) * | 2000-06-12 | 2001-10-16 | Motorola, Inc. | Digital predistortion for amplifiers |
| CN101309253A (en) * | 2007-06-11 | 2008-11-19 | 杭州中科微电子有限公司 | Non-coherent frequency compensation and modulation method and demodulating apparatus |
| US20090051425A1 (en) * | 2007-08-23 | 2009-02-26 | Texas Instruments Incorporated | Predistortion system and method based on look up table interpolation |
| CN101378285A (en) * | 2008-09-28 | 2009-03-04 | 深圳市统先科技股份有限公司 | Method for implementing quadrature frequency conversion in satellite communication high speed demodulator |
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| CN1081551A (en) * | 1992-05-06 | 1994-02-02 | 日本电气株式会社 | Fsk receiver |
| US6304140B1 (en) * | 2000-06-12 | 2001-10-16 | Motorola, Inc. | Digital predistortion for amplifiers |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014029142A1 (en) * | 2012-08-22 | 2014-02-27 | 天津大学 | Radio-frequency front end in high and medium frequency superheterodyne+zero intermediate frequency structure |
| CN108023846A (en) * | 2016-11-04 | 2018-05-11 | 意法设计与应用股份有限公司 | Detect method, circuit, equipment and the computer program product of fsk modulated signal |
| CN108023846B (en) * | 2016-11-04 | 2020-11-03 | 意法设计与应用股份有限公司 | Method, circuit, device and computer program product for detecting FSK modulation signal |
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Application publication date: 20110504 |