CN103427837A - Method for generating wideband numerical control oscillation signal - Google Patents

Method for generating wideband numerical control oscillation signal Download PDF

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CN103427837A
CN103427837A CN2013103801562A CN201310380156A CN103427837A CN 103427837 A CN103427837 A CN 103427837A CN 2013103801562 A CN2013103801562 A CN 2013103801562A CN 201310380156 A CN201310380156 A CN 201310380156A CN 103427837 A CN103427837 A CN 103427837A
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controlled oscillator
look
length
numerical control
address
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CN103427837B (en
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孟桥
于泉涛
陈从颜
平劲松
朱磊
鞠庆
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Southeast University
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Abstract

The invention discloses a method for generating a wideband numerical control oscillation signal which is high in frequency resolution and precision. The method for generating the wideband numerical control oscillation signal comprises the steps that (1) the frequency resolution and the output signal signal-to-noise ratio required by a system are utilized comprehensively, the extraction interval of a lookup table of a numerically controlled oscillator is determined, and an original sine wave table is extracted according to the extraction interval and is used on a hardware memory of the numerically controlled oscillator; (2) truncation processing is carried out on addresses at the address generation end of the numerically controlled oscillator so that the numerical control oscillation signal with high frequency resolution and high precision can be obtained. Compared with an existing numerically controlled oscillator, according to the design of the novel numerically controlled oscillator, the amount of hardware required by the numerically controlled oscillator can be greatly reduced, and the numerical control oscillation signal with high frequency resolution and high precision can be obtained under the condition of limited hardware resources.

Description

A kind of broadband numerical control oscillator signal generation method
Technical field
The present invention relates to a kind of method for designing of digital oscillator, more specifically, relate to for radio receiver, the method for designing of the digital controlled oscillator of the sin cos functions table of the replacement technique based on identical numerical point.
Background technology
At radio reception, it of the same racely has an important application to digital controlled oscillator (NCO, Numerically Controlled Oscillator).Such as the signal of high-speed sampling enters digital circuit, carry out in digital down converter, digital controlled oscillator is important component part wherein, for variable local oscillated signal is provided.Because frequency resolution is high, the frequency easy switching, facilitate the advantages such as Digital Implementation, digital controlled oscillator is applied to the digital circuit aspect of the inside of radio ground receiver.
As Fig. 1, digital controlled oscillator comprises phase accumulator and function generator two large divisions.During Digital Implementation, address accumulator is added up to given incoming frequency control word, obtains the address of corresponding phase under sampling clock.Function generator is exactly a table of natural sines, according to the address obtained, is tabled look-up, and obtains the sine function of corresponding phase.Repeat this process, obtain the sinusoidal sequence of given frequency.
High-speed digital signal often needs the high-speed sampling signal to carry out down-conversion in processing, and need to use the digital controlled oscillator of high freuqency accuracy, high frequency resolution.Common look-up table can be realized high freuqency accuracy, the whole device that swings of high-resolution numerical control, but the length L of the table of natural sines that it needs 0=(f s/ Δ f) N, wherein f sBe the data sampling frequency, Δ f is frequency resolution.When resolution requirement is high, the capacity needed can become very huge.High-speed data is processed f sUsually more than reaching 100MHz, during high-resolution, Δ f is below 1Hz, and length L is 1 * 10 8, a large amount of like this data are difficult to realize storage on current high-speed digital circuit (FPGA etc.).
Another one is common can saving resource the building method of digital controlled oscillator be cordic algorithm, it can rotary mode as the realization of Direct Digital frequency synthesis (DDS), use less resource.But, when realizing with FPGA hardware, due to a large amount of fixed-point algorithms that adopt, while completing the calculating of trigonometric function wherein and antitrigonometric function, there will be some small, uncertain truncated errors, be difficult to reach high freuqency accuracy.For example, by 16 word lengths, press f s=100MHz, Δ f=1Hz produce the sinusoidal signal of f=50MHz, and the frequency departure of actual measurement is about 5mHz.Although its relative error reaches 10 -10, but in the practical application of the high requests such as some deep space TT&Cs, can not meet the demands.
Summary of the invention
Technical problem: the invention provides one under the limited hardware resources supplIes, realize high freuqency accuracy, high-resolution, can reduce the broadband numerical control oscillator signal generation method of digital controlled oscillator to digital hardware resource consumption.
Technical scheme: broadband numerical control oscillator signal generation method of the present invention comprises the following steps:
1) obtain the length L of the look-up table of functions that meets in theory the frequency resolution requirement according to following formula 1:
L 1=f s/ Δ f, wherein, f sFor the system works clock frequency, the frequency resolution of the digital controlled oscillator that Δ f is system requirements;
Then generate L 1The SIN function sequence x of length 1(n),
Figure BDA0000372415460000021
N=0,1 ... L 1-1.
2) according to the signal to noise ratio snr of system requirements, utilize formula
Figure BDA0000372415460000022
Determine the output figure place N of digital controlled oscillator.
3) calculate required digital controlled oscillator look-up table length L according to following formula 2:
L 2=(2 Nπ), the figure place N that wherein N is the numerical control oscillator signal;
Then determine maximum extraction coefficient D max=L 1/ L 2.
4) determine and extract coefficient D according to following condition:
Figure BDA0000372415460000023
And the integral number power that D is 2.
5) according to extracting coefficient D, to the SIN function sequence x generated in step 1) 1(n) evenly extract, obtain extracting the sequence of function x (i) that rear length is L, i.e. x (i)=x 1(1+Di), i=0 ... L-1,
Figure BDA0000372415460000024
6) sequence of function x (i) step 5) generated is according to step 2) the figure place N of definite numerical control oscillator signal, sequence of function x (i) after extracting in step 5) is quantized, the value of the sequence of function after the quantification obtained is saved in look-up table of functions.
7) calculate according to the following formula phase-accumulated step-length λ:
Wherein, the frequency values that f is output signal;
Then phase place being carried out to step-length is the cumulative of λ, generates phase value, using phase value as length, is L 1The address of look-up table of functions.
The address of the look-up table of functions 8) at the address interceptor, step 7) generated is intercepted, the log of low level in the address of the look-up table of functions step 7) generated 2D removes position, the address after being intercepted.
9), under the effect of system clock, numerical value is taken out in the address after the intercepting obtained according to step 8) from look-up table of functions, obtains the numerical control oscillator signal.
Actual table of natural sines, can also be according to its symmetry, the signal value of only storing its front 1/4 cycle is just passable, and the sinusoidal signal of remainder can produce by simple operationss such as anti-pleat, upsets by the signal by front 1/4 cycle, thus further saving resource.These contents are identical with the method for using in general look-up table, repeat no more here.
Goal of the invention of the present invention is achieved in that the principle according to Fig. 1, by EDA design softwares such as VHDL language, designs relevant logic, passes through the comprehensive of relevant eda software, on FPGA or VLSI hardware, realizes.
The inventive method is applied in astronomical ground receiver inside, in high speed signal is processed, realizes the digital controlled oscillator of high frequency resolution, can reduce the consumption of digital controlled oscillator to digital hardware resource.
Beneficial effect: the present invention compared with prior art, has the following advantages:
1) the present invention, according to parameters such as the precision of the output signal frequency of system requirements and signal to noise ratios, the look-up table of functions of a large amount of hardware of occupying of original theory storage area, is extracted according to extraction coefficient definite in method for designing.Look-up table of functions after extraction can reduce data bulk, can convenient realization on hardware.Under limited digital hardware resource, digital controlled oscillator high freuqency accuracy, high-frequency resolution output have been realized.
2) the cumulative phase value of phase accumulator output, intercepted according to figure place definite in method for designing, just can, directly as the address of look-up table of functions, facilitate hardware to realize.
The accompanying drawing explanation
Fig. 1 is the logic diagram of the method flow of broadband numerical control oscillator signal generation;
Fig. 2 is the structured flowchart of broadband digital controlled oscillator.
Embodiment
Detailed description below in conjunction with accompanying drawing to exemplary application of the present invention, can make method for designing of the present invention better be understood.
Fig. 1 is the logic diagram of the method flow of broadband numerical control oscillator signal generation.Fig. 2 is the structured flowchart of broadband digital controlled oscillator.As shown in Figure 2, comprise the phase accumulator part address intercepting transducer that band blocks, the function generator part after storage is extracted, output register according to the digital controlled oscillator of the realization of the inventive method.
1) according to system works clock frequency f sThe frequency resolution Δ f=1Hz of the digital controlled oscillator of=256MHz and system requirements, obtain the length L that meets in theory the look-up table of functions that frequency resolution requires according to following formula 1: L 1=f s/ Δ f=256 * 10 6, approximately need 28 bits to mean, need very large hardware memory space.Then generate L 1The SIN function sequence x of length 1(n),
Figure BDA0000372415460000041
N=0,1 ... L 1-1.
2) require to be greater than 60dB according to the signal to noise ratio snr of system requirements, determine the figure place of numerical control oscillator signal according to formula N = SNR ( dB ) - 1.76 6.02 = 10 .
3) according to the figure place N of digital control signal, according to following formula, calculate required digital controlled oscillator look-up table length L 2: L 2=(2 Nπ) ≈ 3217, the situation of the digital controlled oscillator of general high frequency resolution, L 2Much smaller than L 1.Joint step 1) result is determined maximum extraction coefficient D max=L 1/ L 2=79577;
4) determine and extract coefficient D, according to following condition, determine and extract coefficient D:
Figure BDA0000372415460000043
And the integral number power of D satisfied 2, therefore determine and extract coefficient D=2 14=16384, extract coefficient D and mean sequence x 1(n) every D number is got a some reservation, and all the other are cast out.
5) according to extraction coefficient D=16384, step 1) being obtained to length is 256 * 10 6Sequence of function x 1(n) table evenly extracts, and every 16384 data are got first data and retained, and 16383 data of back are cast out, and obtain extracting the sequence of function x (i) that rear length is L, i.e. x (i)=x 1(Di), i=0 ... L-1,
Figure BDA0000372415460000044
If consider the symmetry of sinusoidal sequence x (i), only store four/one-period in look-up table just passable, can also further resource need to be reduced to original 1/4.
6) sequence of function x (i) step 5) generated is according to step 2) the figure place N of definite numerical control oscillator signal quantized.Quantification is according to quantified precision N position, makes x (n) be multiplied by 2 N-1-1, the value of rounding downwards then.In the present embodiment, according to 10 of quantization digits, make x (n) be multiplied by 2 N-1-1=511, the then value of rounding downwards.The value of the sequence of function after rounding is saved in look-up table of functions.
7) according to the frequency resolution Δ f=1Hz of the numerical control oscillator signal of system requirements and the frequency values f=25.81MHz of output signal, calculate phase-accumulated step-length λ,
Figure BDA0000372415460000051
Phase place is carried out to the cumulative generation phase value that step-length is λ, the address of generating function look-up table namely, now the maximum of address is 256 * 10 6.
The address of the look-up table of functions 8) at the address interceptor, the 7th step generated is intercepted, the log of low level 2D=14 removes position, and after intercepting, the maximum of address is 15625, just and look-up table of functions equal in length.
9) at operating frequency f sUnder the system works clock effect of=256MHz, numerical value is taken out in the address after the intercepting obtained according to step 8) from look-up table of functions, obtains the numerical control oscillator signal of frequency values f=25.81MHz.
In actual use, measured result shows that the frequency resolution Δ f of this numerical control reaches 1Hz, signal to noise ratio meets 60dB and all reaches designing requirement, and any frequency departure do not occur.

Claims (1)

1. a broadband numerical control oscillator signal generation method, is characterized in that, the method comprises the following steps:
1) obtain the length L of the look-up table of functions that meets in theory the frequency resolution requirement according to following formula 1:
L 1=f s/ Δ f, wherein, f sFor the system works clock frequency, the frequency resolution of the digital controlled oscillator that Δ f is system requirements;
Then generate L 1The SIN function sequence x of length 1(n),
Figure FDA0000372415450000011
N=0,1 ... L 1-1;
2) according to the signal to noise ratio snr of system requirements, utilize formula
Figure FDA0000372415450000012
Determine the output figure place N of digital controlled oscillator;
3) calculate required digital controlled oscillator look-up table length L according to following formula 2:
L 2=(2 Nπ), the output figure place N that wherein N is digital controlled oscillator;
Then determine maximum extraction coefficient D max=L 1/ L 2
4) determine and extract coefficient D according to following condition:
Figure FDA0000372415450000013
And the integral number power that D is 2;
5) according to extracting coefficient D, to the SIN function sequence x generated in described step 1) 1(n) evenly extract, obtain extracting the sequence of function x (i) that rear length is L, i.e. x (i)=x 1(1+Di), i=0 ... L-1,
Figure FDA0000372415450000014
6) according to step 2) the figure place N of the output of definite digital controlled oscillator, the sequence of function x (i) after extracting in described step 5) is quantized, the value of the sequence of function after the quantification obtained is saved in look-up table of functions;
7) calculate according to the following formula phase-accumulated step-length λ:
Figure FDA0000372415450000015
Wherein, the frequency values that f is output signal;
Then phase place being carried out to step-length is the cumulative of λ, generates phase value, using described phase value as length, is L 1The address of look-up table of functions;
The address of the look-up table of functions 8) at the address interceptor, described step 7) generated is intercepted, the log of low level in the address of the look-up table of functions step 7) generated 2D removes position, the address after being intercepted;
9), under the effect of system clock, numerical value is taken out in the address after the intercepting obtained according to step 8) from look-up table of functions, just obtains the numerical control oscillator signal.
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Cited By (1)

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CN108897015A (en) * 2018-05-11 2018-11-27 中国人民解放军火箭军工程大学 A kind of emulation navigation satellite signal spurious reduction method

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CN101335509A (en) * 2007-06-29 2008-12-31 大唐移动通信设备有限公司 Method and digital control oscillator for sinusoidal and cosine signal generator
CN101854172A (en) * 2009-04-01 2010-10-06 北京理工大学 Numerical control oscillator parallel design method based on two-dimensional sine table
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CN101335509A (en) * 2007-06-29 2008-12-31 大唐移动通信设备有限公司 Method and digital control oscillator for sinusoidal and cosine signal generator
CN101854172A (en) * 2009-04-01 2010-10-06 北京理工大学 Numerical control oscillator parallel design method based on two-dimensional sine table
JP2011205339A (en) * 2010-03-25 2011-10-13 Toshiba Corp Digitally controlled oscillator

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CN108897015A (en) * 2018-05-11 2018-11-27 中国人民解放军火箭军工程大学 A kind of emulation navigation satellite signal spurious reduction method
CN108897015B (en) * 2018-05-11 2020-11-06 中国人民解放军火箭军工程大学 Simulated navigation satellite signal spurious suppression method

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