CN1119873C - Adaptive amplitude-limiting equalizer for mask CD read-out signal - Google Patents
Adaptive amplitude-limiting equalizer for mask CD read-out signal Download PDFInfo
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- CN1119873C CN1119873C CN 00129795 CN00129795A CN1119873C CN 1119873 C CN1119873 C CN 1119873C CN 00129795 CN00129795 CN 00129795 CN 00129795 A CN00129795 A CN 00129795A CN 1119873 C CN1119873 C CN 1119873C
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Abstract
The present invention belongs to the technical field of high-density digital optical storage. The equalizer of the present invention comprises a signal resolution acquisition unit for acquiring primitive HF signals, an equalizer parameter calculation unit for acquiring characteristic quantity from signals and an amplitude-limiting equalizing link unit for equalizing and compensating read signals. The equalizer can adaptively compensate the variation of different frequency component caused by the variation of optical transfer function. The equalizer of the present invention overcomes intersymbol interference and enhances signal-to-noise ratio, which is a key technology for effectively reading a super-resolution mask optical disc.
Description
Technical field
The invention belongs to the high-density digital field of optical storage technology, particularly be used for the structural design of the equalizer of mask CD read-out signal.
Background technology
The utilization mask layer realizes that the high density storage above the spot size limit is to realize one of important directions of highly dense optical storage.Its structure is to add as one deck mask layer layer 3 between the reflector 2 of common read-only optical disc and dish base 4 as shown in Figure 1, and other parts such as protective layer 1, reflector and dish are basic, and all the CD with common is identical.The material of mask layer reaches at incident light 6 that transmissivity obviously improves under the situation of certain exposure, thereby in irradiation area, forming an effective hot spot less than the irradiation hot spot, be that an effective hot spot is less than the diffraction limit that lambda1-wavelength and object lens 5 are determined, thereby realize the super-resolution storage.Different with common read-only optical disc is, because the hot spot that forms in the mask layer is relevant with exposure in the incident light zone, so the optics amplitude transfer function of system will no longer be a definite value.The optical transfer function (MTF) that has mask CD is all relevant with CD speed and incident optical power, as shown in Figures 2 and 3, among the figure, ordinate optical transfer function, no unit; Horizontal seat is mark tangential spatial frequency (fx), and unit is NA/ λ, and thick line is represented the optical transfer function of common read-only optical disc, and other curve is then represented the optical transfer function of mask CD under different rotating speeds and the incident optical power.Therefrom as can be seen, the spatial-cut-off frequency of mask CD will be higher than common read-only optical disc, and this is the super-resolution effect of mask layer just, but simultaneously as can be seen, because the existence of mask makes that the space transfer function no longer is a definite value.This just requires subsequent process circuit to want and can signal be compensated self adaptation.
Mainly be to use equalizer to come the optical transfer function with low-pass characteristic of compensation optical system in the subsequent compensation circuit in the optical storage system, improve signal to noise ratio.At present, because the optical transfer function of common read-only optical disc is a definite value, so the equalizer that uses is fixing cosine equalizer.The theory diagram of cosine equalizer as shown in Figure 4.Preamplifier A1 in the equalizer is used for isolation signals, and its output impedance equals the surge impedance of delay line.Delay line is with τ signal delay time, and proportional amplifier A2 has then determined balanced amplitude.Then the output amplitude envelope is normalized to,
A(ω)＝1-2acosωτ (1)
Simultaneously can realize that also the expression formula of digital cosine equalizer transfer function is by the digital cosine equalizer:
H(z)＝1-k(z
-2+z
2) (2)
The unit delay of representing in the formula is a clock cycle T in the optical disc encoding.Fig. 5 has represented the action principle of cosine equalizer.Solid line among the figure is the optical transfer function MTF of common read-only optical disc and the amplitude transfer function that dotted line is cosine equalizer, chain-dotted line for both in conjunction with after ssystem transfer function.Abscissa is a frequency among the figure, by
Carried out normalization.As seen, the ssystem transfer function after the isostatic compensation of process cosine equalizer is at working frequency range
Interior amplitude characteristic has improved signal to noise ratio like this near horizontal line.
But have in the CD of mask layer, because the variation of the optical transfer function that mask causes makes that this fixing cosine equalizer is no longer suitable.At first be that cosine equalizer does not possess adaptive characteristic, can't satisfy the requirement of the optical transfer function of offset mask layer disc variations.In addition, cosine equalizer will cause intersymbol interference, particularly when its equilibrium degree increases.So-called intersymbol interference is meant because influences such as the width of cloth of system, phase-frequency characteristic make when receiving end is adjudicated digital influence before and after data are subjected to.Specific to the cosine equalizer in the Disc player, its operation principle as shown in Figure 6.Fig. 6 (a) is read by optical head for different hole dot pattern on the disc, and generates regeneration high frequency (HF) signal shown in Fig. 6 (b), through over-sampling, realizes balanced shown in Fig. 6 (c) according to formula 2 by cosine equalizer.Suppose to disturb between balanced preceding signal nonexistent code, promptly when crossing " 0 " (clipping level), be the ideal decision point.In cosine equalizer, the x (n) that is added in behind-k on duty of x (n-2) and x (n+2) goes up and obtains output z (n).Since the influence of MTF, the signal amplitude difference of different scanning length.In the sweep length difference of the sign indicating number of crossing " 0 " some both sides, under the unequal situation of absolute value of x (n-2) and x (n+2), z (n) value will depart from " 0 " point like this.Like this, when judging, certainly lead to intersymbol interference.Simultaneously for different parametric equalizer k, the degree of intersymbol interference is different and obviously increase with the raising intersymbol interference of equilibrium degree.Owing under intersymbol interference and the common influence of media noise, will produce bigger error code, need handle this problem as the adaptive equalizer of mask CD.This shows that present cosine equilibrium can't be satisfied the equilibrium of mask CD read-out signal.
Summary of the invention
The objective of the invention is for overcoming the weak point of prior art, but design a kind of self adaptation adjustment and eliminate the equalizer of intersymbol interference, make it can adapt to the photochromic mask CD situation that optical transfer function constantly changes when work.Overcome intersymbol interference simultaneously, improved signal to noise ratio.Satisfied the requirement that the mask layer CD effectively reads.
A kind of adaptive amplitude-limiting equalizer that is used for mask CD read-out signal that the present invention proposes, it is characterized in that, comprise the signal resolution degree acquiring unit that obtains original high frequency (HF) signal, from signal, obtain the parametric equalizer computing unit of characteristic quantity and to three unit, the balanced link unit of amplitude limit of the isostatic compensation of read output signal, said signal resolution degree acquiring unit links to each other with said parametric equalizer computing unit, and the balanced link of said amplitude limit unit links to each other with said parametric equalizer computing unit.
Said signal resolution degree acquiring unit can be made of a high pass filter and two amplitude discriminators, the input of one of them amplitude discriminator is connected in the output of said high pass filter, another amplitude discriminator institute input directly obtains original high frequency (HF) signal, and the output of these two amplitude discriminators links to each other with said parametric equalizer computing unit simultaneously.
Said balanced link parameter calculation unit can be made of digital signal processor and the program of working out according to respective algorithms in advance that is stored in wherein.
The balanced link of said amplitude limit unit can be made up of even symmetry high-frequency digital (FIR) filter on an amplitude limiter and coupled one 5 rank.
Balanced link unit of said amplitude limit and balanced link parameter calculation unit all can be made of digital signal processor and the program of working out according to respective algorithms in advance that is stored in wherein.
The structure of adaptive amplitude-limiting equalizer of the present invention as shown in Figure 7.Wherein the balanced link of amplitude limit unit is the core cell of this equalizer, and it finishes the isostatic compensation to read output signal.And signal resolution acquiring unit I and parametric equalizer computing unit II constitute a feedforward path, in order to obtain characteristic quantity and realize self adaptation with this parameter that changes amplitude limiter from signal.Therefore, this system can obtain the signal resolution degree in real time and obtain the parametric equalizer that needs under this equilibrium degree, and then the parameter of adjustment equalizer makes the desirable portfolio effect of acquisition for the read output signal (HF signal) of mask disc.
The composition and the operation principle of each unit are described respectively below:
The balanced link of amplitude limit unit
It is in order to overcome intersymbol interference that the present invention adopts the balanced link of amplitude limit.The balanced link of this amplitude limit can be made up of even symmetry high-frequency digital (FIR) filter on an amplitude limiter and coupled one 5 rank, and its structure as shown in Figure 8.Its operation principle is: the coefficient of this high-frequency digital (FIR) filter for (k, k, 1, k ,-k).Input signal is x (n), equally x (n) is carried out amplitude limit, and the threshold value of amplitude limit is less than or equal to the amplitude of 3T signal, and obtains another sequences y (n).The output signal of amplitude-limiting equalizer can be expressed as like this:
z(n)＝x(n)-k[y(n2-2)-y(n-1)-y(n+1)+y(n+2)]
＝x(n)-k{Limit[x(n-2)]-Limit[x(n-1)]- (3)
Limit[x (n+1)]+Limit[x (n+2)] x (n) is an input signal in the formula, y (n) is the input signal behind the amplitude limit, z (n) is an output signal, k is a parametric equalizer, Limit[x (n)] be the limitation signal of x (n).Since be positioned at the identical half period that the x (n-2) that puts on the level "0" and x (n-1) and x (n+1) and x (n+2) are in identical sweep length, so have:
Limit[x(n-2)]＝Limit[x(n-1)] (4)
Limit[x (n+2)]=Limit[x (n+1)] like this, owing to crossing " 0 " some place, (4) formula always satisfies, and therefore can not produce additional intersymbol interference.The operation principle of the balanced link of this amplitude limit unit as shown in Figure 9, the amplitude of amplitude limit is the amplitude of highest frequency component in the CD read-out signal.As can be seen from the figure, because the processing of symmetry, the zero crossing place can not produce intersymbol interference.
Signal resolution degree acquiring unit and balanced link parameter calculation unit
As previously mentioned, feedforward path of the common formation in these two unit of signal resolution degree acquiring unit and balanced link parameter calculation unit is in order to change the parameter of balanced link.Signal resolution degree acquiring unit is made of a high pass filter and two amplitude discriminators, and balanced link parameter calculation unit is made of according to respective algorithms digital signal processor (DSP).Its operation principle is: original high frequency (HF) signal now passes through high pass filter, and the cut-off frequency of high pass is located between 3T and the 4T, can obtain the signal of 3T like this.This signal is carried out the amplitude I3 that amplitude discrimination just can obtain the 3T signal.Amplitude discrimination is directly carried out to high frequency (HF) signal in another road, because the amplitude of 11T signal is the peak in all frequency components in high frequency (HF) signal.Therefore, directly just can obtain the amplitude I11 of 11T signal to high frequency (HF) signal amplitude discrimination.Two amplitude signals are divided by just can obtain the resolution Reso of this signal.Calculate required parametric equalizer k by resolution, enter the balanced link of amplitude limit and carry out equilibrium, so just can realize adaptive equalization.
For amplitude-limiting equalizer of the present invention, on the 3T signal frequency, the amplitude of equalizer is exactly the amplitude on this frequency of 5 rank high-frequency digital (FIR) filters wherein.The transfer function of 5 rank high-frequency digitals (FIR) in the amplitude-limiting equalizer is:
H (ω)=1+k (e
-j ω+ e
J ω)-k (e
-j2 ω+ e
J2 ω)=1+2kcos (ω)-2kcos (2 ω) (5) is for the 11T signal, because the amplitude height, the cycle is long, when its crest and trough, (4) formula also satisfies, and therefore the multiplication factor perseverance of equalizer is 1 on the frequency of 11T signal, and the equilibrium degree that can obtain this equalizer thus is:
Can draw the relation between the resolution Reso of amplitude-limiting equalizer parameter k and signal
(7) formula is the balance parameters algorithm of this equalizer.
The present invention has following characteristics and useful effect:
The present invention mainly is a kind of adaptive equalizer that is adapted to mask CD, and its main points are the balanced link of adaptive structure and amplitude limit.In order to realize self adaptation, just need from CD read-out signal, obtain required parameter.Because CD adopts eight-14 modulation (EFM) at present.Highest frequency is the signal of half period 3T to the read output signal of CD (being commonly referred to as the HF signal), and low-limit frequency is to be the signal of 11T the half period.By the low-pass characteristic of MTF as can be known, the amplitude minimum of 3T signal in CD read-out signal and the amplitude maximum of 11T signal, and the amplitude of other frequency component is all between the two.So as long as carry out efficient balance for 3T and 11T amplitude, other amplitude is also corresponding to be satisfied.In compact disk standards, the 3T/11T in high frequency (HF) signal is called as the resolution of signal.So can carry out the self adaptation adjustment to parametric equalizer by the resolution of obtaining high frequency (HF) signal, realize adaptive equalization.
The present invention uses the CD-R CD that becomes the power imprinting to simulate the CD read-out signal of different resolutions.And carry out equilibrium with this adaptive amplitude-limiting equalizer and test.The high frequency that obtains (HF) signal has different signal resolution degree, and has obtained balanced parameter k by (7) formula, and is as shown in table 1
Table 1 experimental signal resolution and parametric equalizer
Carry out the equilibrium experiment for these three signals.Figure 10～12 are these three signal equalizations comparison diagrams as a result, wherein Figure 10 (a), Figure 11 (a) are these three primary signals with different resolutions with Figure 12 (a), and Figure 10 (b), Figure 11 (b) and Figure 12 (b) then are that these three signals are by the signal behind the adaptive amplitude-limiting equalizer.From experimental result as seen, though the resolution difference of primary signal, (wherein a-signal has than high-resolution, the resolution of C signal is then lower), but through after the adaptive equalizer, the radio-frequency component of signal all obtains suitable amplification, makes signal resolution degree after the equilibrium near 1, and promptly the signal amplitude of different frequency component is about equally in the signal.Therefore, this equalizer can both effectively carry out equilibrium for the CD read-out signal (high frequency (HF) signal) of different resolutions, improves the signal to noise ratio of signal.
| The signal numbering | The signal resolution degree | Amplitude-limiting equalizer parameter k |
| A | 0.8083 | 0.1186 |
| B | 0.7378 | 0.1777 |
| C | 0.6113 | 0.3179 |
Description of drawings
Fig. 1 is a mask layer optical disk structural representation.
Fig. 2 is the MTF on the mask CD fx direction and the graph of a relation of disc rotation speed.
Fig. 3 is the MTF on the mask CD fx direction and the graph of a relation of incident optical power.
Fig. 4 is existing cosine equalizer schematic diagram.
Fig. 5 is the balanced schematic diagram of cosine equalizer to MTF.
Fig. 6 is a cosine equalizer operation principle schematic diagram.
Fig. 7 is an adaptive amplitude-limiting equalizer structural representation of the present invention.
Fig. 8 is the composition frame chart of the balanced link of amplitude limit of the present invention.
Fig. 9 is the balanced link work of an amplitude limit of the present invention schematic diagram.
Figure 10 is that the present invention is to a-signal equilibrium result contrast signal figure.
Figure 11 for the present invention to B signal equalization contrast signal figure as a result.
Figure 12 for the present invention to C signal equalization contrast signal figure as a result.
The quadravalence high pass Butterworth filter circuit theory diagrams that Figure 13 adopts for embodiments of the invention.
Figure 14 is the amplitude-frequency and the phase frequency figure of the quadravalence Butterworth high pass filter among Figure 13.
Figure 15 mimic high pass filter measured signal
The amplitude discrimination circuit schematic diagram that Figure 16 adopts for embodiments of the invention.
Embodiment
The adaptive amplitude-limiting equalizer embodiment that the present invention is used for mask CD read-out signal is described with reference to the accompanying drawings as follows:
The example structure of adaptive amplitude-limiting equalizer of the present invention is by signal resolution degree acquiring unit I, and the balanced link of parametric equalizer computing unit II and amplitude limit unit is formed, as shown in Figure 7.Wherein, the balanced link of the balanced link parameter calculation unit of present embodiment and amplitude limit unit all is to carry out after signal sampling and digitlization, because algorithm is simpler and clearer, according to the formula that provides above, realizes in a digital signal processor (DSP).Signal resolution degree acquiring unit is an analog circuit, is made up of high pass and two links of amplitude discrimination.The high pass link of present embodiment is selected general 4 rank Butterworth (Butterworth) high pass filters for use, and cut-off frequency is 700Hz, is about the signal of 3.1T.Particular circuit configurations and parameter as shown in figure 13, the capacitance-resistance parameter is among the figure: capacitance is 200pF, R
502=1.05K, R
508=1.23K, R
503=1.49K, R
509=0.869K, all the other resistances are 10K.The amplitude-frequency of this circuit and phase-frequency characteristic are as shown in figure 14.Figure 15 is the experimental result of actual high frequency (HF) signal by this high pass circuit, and " 1 " road signal is original high frequency (HF) signal among the figure; " 2 " road signal is by high frequency (HF) signal after the high pass link.Therefrom as can be seen, the high pass link has stronger inhibitory action for frequency less than the component of 3T signal, the 3T signal is not then suppressed, thereby guaranteed subsequent conditioning circuit correct detect the I3 amplitude.All obtain the positive negative peak of 3T and 11T signal through high frequency (HF) signal of filtering and original high frequency (HF) signal via amplitude discrimination circuit, and obtain thus I3 and I11 value.The amplitude discrimination circuit of present embodiment adopts general amplitude discrimination circuit, is made up of unidirectional peak value detection and capacitance-resistance amplitude holding circuit that diode and operational amplifier constitute, and circuit as shown in figure 16.
After obtaining the positive negative peak of I3 and I11, can obtain corresponding numerical value by AD sampling, obtain the resolution of signal through computing, and and then have dsp chip to draw the parameter k of adaptive equalizer, realize balanced self adaptation.
Claims (5)
1, a kind ofly is used for the adaptive amplitude-limiting equalizer that mask CD is read high-frequency signal, it is characterized in that, comprise the signal resolution degree acquiring unit that obtains original high-frequency signal, from this signal, obtain the parametric equalizer computing unit of characteristic quantity and to three unit, the balanced link unit of amplitude limit of the isostatic compensation of read output signal, said signal resolution degree acquiring unit links to each other with said parametric equalizer computing unit, and the balanced link of said amplitude limit unit links to each other with said parametric equalizer computing unit.
2, adaptive amplitude-limiting equalizer as claimed in claim 1, it is characterized in that, said signal resolution degree acquiring unit is made of a high pass filter and two amplitude discriminators, the input of one of them amplitude discriminator is connected in the output of said high pass filter, the input of another amplitude discriminator directly obtains original high-frequency signal, and the output of these two amplitude discriminators links to each other with said parametric equalizer computing unit simultaneously.
3, adaptive amplitude-limiting equalizer as claimed in claim 1 is characterized in that, said parametric equalizer computing unit is by digital signal processor and be stored in constituting according to the program of respective algorithms establishment in advance wherein.
4, adaptive amplitude-limiting equalizer as claimed in claim 1 is characterized in that, said amplitude-limiting equalizer unit is made up of the even symmetry high-frequency digital filter on an amplitude limiter and coupled one 5 rank.
5, adaptive amplitude-limiting equalizer as claimed in claim 1 is characterized in that, said amplitude-limiting equalizer unit and parametric equalizer computing unit are by digital signal processor and be stored in constituting according to the program of respective algorithms establishment in advance wherein.
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| CN 00129795 CN1119873C (en) | 2000-10-13 | 2000-10-13 | Adaptive amplitude-limiting equalizer for mask CD read-out signal |
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| CN 00129795 CN1119873C (en) | 2000-10-13 | 2000-10-13 | Adaptive amplitude-limiting equalizer for mask CD read-out signal |
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| CN101079273B (en) * | 2006-03-14 | 2010-09-08 | 株式会社理光 | Data reproducing method, data reproducing device, compact disc and data recording/reproducing device |
| CN106128449B (en) * | 2016-08-16 | 2023-09-01 | 青岛歌尔声学科技有限公司 | Active noise reduction method for automobile |
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