CN103427837B - A kind of broadband digital oscillator generation method - Google Patents

A kind of broadband digital oscillator generation method Download PDF

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CN103427837B
CN103427837B CN201310380156.2A CN201310380156A CN103427837B CN 103427837 B CN103427837 B CN 103427837B CN 201310380156 A CN201310380156 A CN 201310380156A CN 103427837 B CN103427837 B CN 103427837B
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controlled oscillator
digital controlled
look
address
sequence
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CN103427837A (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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Southeast University
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Abstract

The invention discloses a kind of high frequency resolution, high-precision numerical control oscillation signal generation method.The frequency resolution that this numerical control oscillation signal generation method utilization system requires and output signal-noise ratio, determine the extraction interval of the look-up table of digital controlled oscillator, then according to extraction interval original sine wave table to be extracted and in the hardware memory of digital controlled oscillator; Then produce end in the address of digital controlled oscillator and truncation is carried out to address, thus realize the numerical control oscillation signal of high freuqency accuracy, high frequency resolution.The design of this novel numerical control oscillator of the present invention, more existing digital controlled oscillator, can save the hsrdware requirements of digital controlled oscillator greatly, realizes the digital controlled oscillator signal of high freuqency accuracy, high frequency resolution under limited hardware resource condition.

Description

A kind of broadband digital oscillator 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, based on the method for designing of the digital controlled oscillator of the sin cos functions table of the replacement technique of identical numerical point.
Background technology
At radio reception, it of the same racely has important application to digital controlled oscillator (NCO, NumericallyControlledOscillator).The signal of such as high-speed sampling enters digital circuit and carries out in digital down converter, and digital controlled oscillator is important component part wherein, for providing variable local oscillated signal.Because frequency resolution is high, frequency error factor convenient, 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 sum functions generator two large divisions.During Digital Implementation, address accumulator adds 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, tables look-up in the address according to obtaining, and obtains the sine function of corresponding phase.Repeat this process, obtain the sinusoidal sequence of given frequency.
In high-speed digital video camera, often need high-speed sampling signal to carry out down-conversion, need the digital controlled oscillator using high freuqency accuracy, high frequency resolution.Common look-up table can realize high freuqency accuracy, high-resolution numerical control is whole swings device, but the length L of the table of natural sines of its needs 0=(f s/ Δ f) N, wherein f sbe data sampling frequency, Δ f is frequency resolution.When resolution requirement is high, the capacity of needs can become very huge.High-speed data process f susually reach more than 100MHz, during high-resolution, Δ f is at below 1Hz, and length L is 1 × 10 8, data a large amount of are like this difficult to realize storing on current high-speed digital circuit (FPGA etc.).
What another one was common can the building method of digital controlled oscillator of saving resource be cordic algorithm, it can rotary mode as the realization of direct digital synthesis technique (DDS), use less resource.But, when with FPGA hardware implementing, due to the fixed-point algorithm adopted in a large number, when completing the calculating of trigonometric function wherein and antitrigonometric function, there will be that some are small, uncertain truncated error, be difficult to reach high freuqency accuracy.Such as, by 16 word lengths, by 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 -10but, 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 limited hardware resource condition, realize high freuqency accuracy, high-resolution, can reduce the wideband numerical control oscillation signal generation method of digital controlled oscillator to digital hardware resource consumption.
Technical scheme: wideband numerical control oscillation signal generation method of the present invention, comprises the following steps:
1) the length L of the look-up table of functions meeting frequency resolution requirements is in theory obtained according to following formula 1:
L 1=f s/ Δ f, wherein, f sfor system works clock frequency, Δ f is the frequency resolution of the digital controlled oscillator of system requirements;
Then L is generated 1the SIN function sequence x of length 1(n), namely x 1 ( n ) = s i n ( 2 π n L 1 ) , n = 0 , 1 , ... L 1 - 1.
2) according to the signal to noise ratio snr of system requirements, formula is utilized the unit of signal to noise ratio snr is dB, determines the output figure place N of digital controlled oscillator, wherein expression rounds up.
3) required digital controlled oscillator look-up table length L is calculated according to following formula 2:
L 2=(2 nπ), wherein N is the figure place of the output of numerical control oscillation signal ;
Then maximum extraction coefficient D is determined max=L 1/ L 2.
4) determine to extract coefficient D according to following condition: and D is the integral number power of 2.
5) according to extraction coefficient D, to step 1) the middle SIN function sequence x generated 1n () is evenly extracted, 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, wherein represent and round downwards.
6) by step 5) sequence of function x (i) that generates is according to step 2) the figure place N of numerical control oscillation signal that determines, to step 5) in extract after sequence of function x (i) quantize, be saved in look-up table of functions by the value of the sequence of function after the quantification obtained, the concrete grammar of described quantification is: sequence of function x (i) is multiplied by (2 n-1-1), the value of the sequence of function after being multiplied is rounded downwards.
7) phase-accumulated step-length λ is calculated according to the following formula:
wherein, f is the frequency values of output signal;
Then carrying out step-length to phase place is the cumulative of λ, generates phase value, is L using phase value as length 1the address of look-up table of functions.
8) at address interceptor to step 7) address of look-up table of functions that generates intercepts, namely step 7) log of low level in the address of look-up table of functions that generates 2d removes position, obtains the address after intercepting.
9) under the effect of system clock, according to step 8) address after the intercepting that obtains, from look-up table of functions, take out numerical value, obtain numerical control oscillation signal.
Actual table of natural sines, can also according to its symmetry, the signal value only storing its front 1/4 cycle is just passable, and the sinusoidal signal of remainder can by the signal in front 1/4 cycle by simple operations generations such as anti-pleat, upsets, thus can saving resource further.These contents are identical with the method used 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, and by EDA design softwares such as VHDL language, the logic that design is relevant, passes through the comprehensive of relevant eda software, FPGA or VLSI hardware realizes.
It is inner that the inventive method is applied in astronomical ground receiver, in igh-speed wire-rod production line, 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 is 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 occupying a large amount of hardware storage space of original theory, extracts according to the extraction coefficient determined in method for designing.Look-up table of functions after extraction can decrease data bulk, can conveniently on hardware realize.Under limited digital hardware resource, achieve digital controlled oscillator high freuqency accuracy, high-frequency differentiates output.
2) accumulated phase value of phase accumulator output, intercepts according to the figure place determined in method for designing, just directly as the address of look-up table of functions, can facilitate hardware implementing.
Accompanying drawing explanation
Fig. 1 is the logic diagram of the method flow that wideband numerical control oscillation signal generates;
Fig. 2 is the structured flowchart of wideband numerical control oscillator.
Embodiment
Below in conjunction with the detailed description of accompanying drawing to exemplifying application, method for designing of the present invention can be made better to be understood.
Fig. 1 is the logic diagram of the method flow that wideband numerical control oscillation signal generates.Fig. 2 is the structured flowchart of wideband numerical control oscillator.As shown in Figure 2, comprise according to the digital controlled oscillator of the realization of the inventive method and be with the phase accumulator part address blocked to intercept transducer, store the function generator part after extracting, output register.
1) according to system works clock frequency f sthe frequency resolution Δ f=1Hz of the digital controlled oscillator of=256MHz and system requirements, obtains the length L of the look-up table of functions meeting frequency resolution requirements in theory according to following formula 1: L 1=f s/ Δ f=256 × 10 6, approximately need 28 bits to represent, need very large hardware memory space.Then L is generated 1the SIN function sequence x of length 1(n), namely x 1 ( n ) = s i n ( 2 π n L 1 ) , n = 0 , 1 , ... L 1 - 1.
2) require to be greater than 60dB, according to the figure place of formula determination numerical control oscillation signal according to the signal to noise ratio snr of system requirements
3) according to the figure place N of digital control signal, required digital controlled oscillator look-up table length L is calculated according to following formula 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 determine maximum extraction coefficient D max=L 1/ L 2=79577;
4) determine to extract coefficient D, determine to extract coefficient D according to following condition: and D meets the integral number power of 2, therefore determine to extract coefficient D=2 14=16384, extract coefficient D and represent sequence x 1n () every D number is got a point and is retained, all the other are cast out.
5) according to extraction coefficient D=16384 to step 1) to obtain length be 256 × 10 6sequence of function x 1n () table evenly extracts, every 16384 data are got first data and retained, and 16383 data are below 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, if consider the symmetry of sinusoidal sequence x (i), only store four/one-period in a lookup table just passable, resource can also be needed to be reduced to original 1/4 further.
6) by step 5) sequence of function x (i) that generates is according to step 2) the figure place N of numerical control oscillation signal that determines quantizes.Quantification is according to quantified precision N position, makes x (i) be multiplied by 2 n-1-1, then round value downwards.In the present embodiment, according to quantization digit 10, x (i) is made to be multiplied by 2 n-1-1=511, then rounds value 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 oscillation signal of system requirements and the frequency values f=25.81MHz of output signal, phase-accumulated step-length λ is calculated, carry out to phase place the Accumulating generation phase value that step-length is λ, the namely address of generating function look-up table, now the maximum of address is 256 × 10 6.
8) intercept, the log of low level in the address of address interceptor to the look-up table of functions that the 7th step generates 2d=14 removes position, and after intercepting, the maximum of address is 15625, and the length with regard to sum functions look-up table is equal.
9) at operating frequency f sunder the system works clock effect of=256MHz, according to step 8) address after the intercepting that obtains, from look-up table of functions, take out numerical value, obtain the numerical control oscillation 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 do not occur any frequency departure.

Claims (1)

1. a wideband numerical control oscillation signal generation method, it is characterized in that, the method comprises the following steps:
1) the length L of the look-up table of functions meeting frequency resolution requirements is in theory obtained according to following formula 1:
L 1=f s/ Δ f, wherein, f sfor system works clock frequency, Δ f is the frequency resolution of the digital controlled oscillator of system requirements;
Then L is generated 1the SIN function sequence x of length 1(n), namely n=0,1 ... L 1-1;
2) according to the signal to noise ratio snr of system requirements, formula is utilized the unit of signal to noise ratio snr is dB, determines the output figure place N of digital controlled oscillator, wherein expression rounds up;
3) required digital controlled oscillator look-up table length L is calculated according to following formula 2:
L 2=(2 nπ), wherein N is the figure place of the output of digital controlled oscillator;
Then maximum extraction coefficient D is determined max=L 1/ L 2;
4) determine to extract coefficient D according to following condition: and D is the integral number power of 2;
5) according to extraction coefficient D, to described step 1) the middle SIN function sequence x generated 1n () is evenly extracted, 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, wherein represent and round downwards;
6) according to step 2) the figure place N of the output of digital controlled oscillator that determines, to described step 5) in extract after sequence of function x (i) quantize, be saved in look-up table of functions by the value of the sequence of function after the quantification obtained, the concrete grammar of described quantification is: sequence of function x (i) is multiplied by (2 n-1-1), the value of the sequence of function after being multiplied is rounded downwards;
7) phase-accumulated step-length λ is calculated according to the following formula:
wherein, f is the frequency values of output signal;
Then carrying out step-length to phase place is the cumulative of λ, generates phase value, is L using described phase value as length 1the address of look-up table of functions;
8) at address interceptor to described step 7) address of look-up table of functions that generates intercepts, namely step 7) log of low level in the address of look-up table of functions that generates 2d removes position, obtains the address after intercepting;
9) under the effect of system clock, according to step 8) address after the intercepting that obtains, from look-up table of functions, take out numerical value, just obtain numerical control oscillation signal.
CN201310380156.2A 2013-08-27 2013-08-27 A kind of broadband digital oscillator generation method Expired - Fee Related CN103427837B (en)

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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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