CN203590206U - Preprocessing structure before image digital-to-analog conversion - Google Patents
Preprocessing structure before image digital-to-analog conversion Download PDFInfo
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- CN203590206U CN203590206U CN201320675239.XU CN201320675239U CN203590206U CN 203590206 U CN203590206 U CN 203590206U CN 201320675239 U CN201320675239 U CN 201320675239U CN 203590206 U CN203590206 U CN 203590206U
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- 238000006243 chemical reaction Methods 0.000 title claims abstract description 17
- 238000007781 pre-processing Methods 0.000 title claims abstract description 10
- 238000005070 sampling Methods 0.000 claims abstract description 26
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Abstract
The utility model provides a preprocessing structure before image digital-to-analog conversion. The preprocessing structure allows signals having different frequencies to pass through a digital analog converter and output amplitudes of the signals to remain unchanged, quality of high-frequency component signals is improved, and working efficiency of the digital analog converter is doubled. Formed digital signals after conversion through the digital analog converter pass through an inverse-sinc function digital filter and an interpolation digital filter in order and then are accessed to the digital analog converter, the inverse-sinc function digital filter and the interpolation digital filter form a preprocessing module, a clock which is accessed to the inverse-sinc function digital filter is a sampling clock of an input signal, a clock which is accessed to the interpolation digital filter and the digital analog converter is a clock having a frequency which is twice a frequency of the sampling clock of the input signal, and a corresponding clock connecting portion between the inverse-sinc function digital filter and the interpolation digital filter is provided with a phase-locked loop.
Description
Technical field
The utility model relates to protection and monitor field, is specially the pre-processing structure before a kind of image digital-to-analogue conversion.
Background technology
Society security protection becomes more and more important, and safety monitoring basic process is the camera collection image that is monitored district, and converts digital data transmission to monitoring end by analog to digital converter, by digital to analog converter, is converted to analog signal and is driven monitor.The transmission of a large amount of monitoring images becomes an important bottleneck of system, in order to raise the efficiency, reduces cost, the transmission of multiway images becomes main flow, and way is more and more, develops into even 16 tunnels of 4 tunnels, 8 tunnels from single, double road, way means that amount of image information is larger more.Yet be subject to the pressure of system cost, transmittability does not allow significantly to improve, this reduces with regard to meaning the amount of information that every road image allows, and way is more, and the clock frequency of every road image sampling reduces, even substantially just met Nyquist law, be the doubled frequency of signal bandwidth, under the condition of this low sampling rate, the characteristic of digital to analog converter self just becomes bottleneck, digital picture is when digital to analog converter reverts to analog signal, and picture quality will go wrong.
Monitoring image way is more, and synthetic amount of information is larger, and in the situation that transmission rate is constant, the amount of information of giving every road monitoring image reduces, and in other words, the sampling clock frequency of every road image reduces.In order to guarantee that aliasing does not occur image, the lower limit of clock frequency is the twice of signal bandwidth, i.e. nyquist frequency.
Analog signal is through an analog to digital converter generating digital signal, as shown in Figure 1, process can be understood as a continuous signal data1, with clock fclk sampling quantity, change into discrete digital signal, as A, B, C, D, E, and digital signal through digital to analog converter as shown in Figure 2, process can be understood as the corresponding analog quantity of a-signal and keeps T1～T2 time, the corresponding analog quantity of B signal keeps T2～T3 time, the corresponding analog quantity of C signal keeps T3～T4 time, and the corresponding analog quantity of D signal keeps T4～T5 time.
The amplitude-frequency characteristic that has proved digital to analog converter on mathematics is a sinc function, i.e. sinx/x, and its amplitude frequency curve, as Fig. 3, can see that from figure the signal of different frequency has passed through digital to analog converter output, there is different variations in amplitude.When signal frequency fs approaches a half of clock frequency, i.e. the limit of frequency of utilization, output amplitude has fallen approximately 36%, i.e. 3.9dB.In other words, after digital to analog converter, the lowest frequency components of signal and highest frequency component changes in amplitude can differ 36%, and this greatly reduces picture quality.When the clock frequency of digital to analog converter is during far above signal bandwidth, digital to analog converter is no impact also, but signal frequency approaches clock frequency one half, and picture quality has just obviously declined.
Sampling clock frequency due to image is only the twice of signal bandwidth simultaneously, means the sampled point of high-frequency signal one-period seldom, when extreme, only has 2 points, and picture quality also declines.
Summary of the invention
For existing above-mentioned defect, the utility model provides the pre-processing structure before a kind of image digital-to-analogue conversion, and it makes the signal of different frequency through digital to analog converter, and output amplitude remains unchanged; And high frequency signal quality is improved; The operating frequency of digital to analog converter is doubled.
Pre-processing structure before a kind of image digital-to-analogue conversion, it is characterized in that: the digital signal forming after analog to digital converter conversion is in turn by anti-sinc function digit filter, after interpolation digital filter, access digital to analog converter, described anti-sinc function digit filter, interpolation digital filter forms pretreatment module, the sampling clock that the clock of described anti-sinc function digit filter access is input signal, described interpolation digital filter, the clock of the sampling clock frequency twice that the clock of digital to analog converter access is input signal, described anti-sinc function digit filter, the corresponding clock junction of interpolation digital filter is provided with phase-locked loop.
Preprocess method before a kind of image digital-to-analogue conversion, it is characterized in that: when the sample rate of picture signal approaches the twice of vision bandwidth, while being nyquist frequency, the digital signal forming after analog to digital converter conversion is accessed to digital to analog converter after amplitude preliminary treatment and interpolation again, amplitude preliminary treatment refers to an anti-sinc function, be x/sinx function, signal amplitude is compensated; Interpolation refers to inserts a new digital signal between two adjacent digital signals, make each cycle in high-frequency signal obtain more sampled point, the working clock frequency of interpolation is the twice of the sampling clock frequency of input signal, the work clock of described analog to digital converter is the twice of the sampling clock frequency of input signal, and wherein anti-sinc function and interpolation all can adopt digital filter to realize.
It is further characterized in that:
Anti-sinc function digit filter completes amplitude preliminary treatment, anti-sinc function, the amplitude-frequency characteristic of x/sinx function is that signal frequency is higher, the amplitude of output is larger, digital signal can make the signal of different frequency through digital to analog converter through anti-sinc function compensation, and the amplitude of output remains unchanged;
Interpolation digital filter completes interpolation function, a new digital signal of inserting between two adjacent digital signals in interpolation process, this new digital signal is that two adjacent digital signals are processed and calculated by interpolation digital filter, interpolation is equivalent to sample rate and is doubled, and allows digital to analog converter be operated in higher frequency;
The sampling clock that the clock of described anti-sinc function digit filter access is input signal, the corresponding clock junction of described anti-sinc function digit filter, interpolation digital filter is provided with phase-locked loop, and described phase-locked loop makes the twice of the sampling clock frequency that the frequency of subsequent clock is input signal.
When the sample rate of picture signal approaches the twice of vision bandwidth, during nyquist frequency, the impact very large on the mass formation of image of the characteristic of digital to analog converter self, at this moment will carry out preliminary treatment and overcome these impacts preparing the image of conversion.Adopt after the utility model, by digital signal is carried out to amplitude preliminary treatment and interpolation, the sinc function amplitude-frequency characteristic that wherein anti-sinc function digit filter object is exactly logarithmic mode transducer self is carried out precompensation, anti-sinc function amplitude-frequency characteristic is that signal frequency is higher, the amplitude of output is larger, this characteristic is just in time contrary with sinc function, digital signal is first passed through anti-sinc function like this, the amplitude of HFS first increases, again through after the reducing of the sinc function amplitude-frequency characteristic of digital to analog converter self, remain unchanged, therefore it has passed through anti-sinc function and digital to analog converter, under each frequency, the amplitude of signal just remains unchanged, solved the signal of different frequency through digital to analog converter, output amplitude changes different problems, the effect of interpolation digital filter is process algorithm between two signals, inserts a value of calculating, and visual quality is improved, and due to the twice of the work clock of the analog to digital converter sampling clock frequency that is input signal, its operating frequency by digital to analog converter is doubled, to sum up, it makes the signal of different frequency through digital to analog converter, and output amplitude remains unchanged, and high frequency signal quality is improved, the operating frequency of digital to analog converter is doubled.
Accompanying drawing explanation
Fig. 1 is the schematic diagram of analog to digital converter sampled signal;
Fig. 2 is the schematic diagram of digital to analog converter output waveform;
Fig. 3 is sinc function amplitude-frequency characteristic schematic diagram;
Fig. 4 is structural representation schematic diagram of the present utility model;
Fig. 5 is anti-sinc function amplitude-frequency characteristic schematic diagram;
Fig. 6 is phase-locked loop input-output wave shape schematic diagram;
Fig. 7 is digital-to-analogue output waveform schematic diagram before signal interpolation;
Fig. 8 is digital-to-analogue output waveform schematic diagram after signal interpolation.
Embodiment
Pre-processing structure before a kind of image digital-to-analogue conversion, see Fig. 4: the digital signal forming is in turn by anti-sinc function digit filter after analog to digital converter conversion, after interpolation digital filter, access digital to analog converter, described anti-sinc function digit filter, interpolation digital filter forms pretreatment module, the sampling clock that the clock of described anti-sinc function digit filter access is input signal, described interpolation digital filter, the clock of the sampling clock frequency twice that the clock of digital to analog converter access is input signal, described anti-sinc function digit filter, the corresponding clock junction of interpolation digital filter is provided with phase-locked loop.
Preprocess method before a kind of image digital-to-analogue conversion, when the sample rate of picture signal approaches the twice of vision bandwidth, while being nyquist frequency, the digital signal forming after analog to digital converter conversion is accessed to digital to analog converter after amplitude preliminary treatment and interpolation again, amplitude preliminary treatment refers to an anti-sinc function, be x/sinx function, signal amplitude is compensated; Interpolation refers to inserts a new digital signal between two adjacent digital signals, make each cycle in high-frequency signal obtain more sampled point, the working clock frequency of interpolation is the twice of the sampling clock frequency of input signal, the twice of the sampling clock frequency that the work clock of described analog to digital converter is input signal.Wherein anti-sinc function and interpolation all can adopt digital filter to realize.
Anti-sinc function digit filter completes amplitude preliminary treatment, anti-sinc function, the amplitude-frequency characteristic of x/sinx function is that signal frequency is higher, the amplitude of output is larger, digital signal can make the signal of different frequency through digital to analog converter through anti-sinc function compensation, and the amplitude of output remains unchanged; Interpolation digital filter completes interpolation function, a new digital signal of inserting between two adjacent digital signals in interpolation process, this new digital signal is that two adjacent digital signals are processed and calculated by interpolation digital filter, interpolation is equivalent to sample rate and is doubled, and allows digital to analog converter be operated in higher frequency; The sampling clock that the clock of described anti-sinc function digit filter access is input signal, the corresponding clock junction of described anti-sinc function digit filter, interpolation digital filter is provided with phase-locked loop, and described phase-locked loop makes the twice of the sampling clock frequency that the frequency of subsequent clock is input signal.
Its whole operation principle is described below: the object of anti-sinc function digit filter module is exactly that the sinc function amplitude-frequency characteristic of logarithmic mode transducer self is carried out precompensation.The amplitude-frequency characteristic of anti-sinc function digit filter is shown in Fig. 5, and this amplitude-frequency characteristic is that signal frequency is higher, and the amplitude of output is larger, and this characteristic is just in time contrary with sinc function.Digital signal is first passed through anti-sinc function digit filter like this, and the amplitude of HFS first increases, then through after the reducing of the sinc function amplitude-frequency characteristic of digital to analog converter self, remains unchanged.Passed through anti-sinc function digit filter, and digital to analog converter, under each frequency, the amplitude of signal just remains unchanged.Solved the signal of different frequency through digital to analog converter, output amplitude changes different problems.
The effect of interpolation digital filter module is process algorithm between two signals, inserts a value of calculating; As shown in Figure 7, Figure 8, traditional digital to analog converter output A, B, C, tetra-signals of D, passed through interpolation digital filter, between A, B signal, insert signal I1, between B, C signal, insert signal I2, between C, D signal, insert signal I3, A represents with A, B, C, 4 of D to the signal tradition between D like this, for new departure, A, I1, B, I2, C, I3,7 of D represent, the quality of image improves.
Because the semaphore of interpolation is many one times, the twice of the sampling clock that the work clock of interpolation digital filter is input signal, this needs a phase-locked loop to complete.As shown in Figure 6, the function of phase-locked loop is to produce a clock that frequency is input signal sampling clock fclk twice.Through interpolation, can see, during classical signal process digital to analog converter, the working clock frequency of digital to analog converter is identical with input signal sampling clock.And the work clock of digital to analog converter is the twice of input signal sampling clock frequency after interpolation.Before to mention the frequency of bandwidth ratio digital to analog converter work of signal lower, digital to analog converter self is lower on the impact of signal.
Claims (1)
1. the pre-processing structure before an image digital-to-analogue conversion, it is characterized in that: the digital signal forming after analog to digital converter conversion is in turn by anti-sinc function digit filter, after interpolation digital filter, access digital to analog converter, described anti-sinc function digit filter, interpolation digital filter forms pretreatment module, the sampling clock that the clock of described anti-sinc function digit filter access is input signal, described interpolation digital filter, the clock of the sampling clock frequency twice that the clock of digital to analog converter access is input signal, described anti-sinc function digit filter, the corresponding clock junction of interpolation digital filter is provided with phase-locked loop.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103560793A (en) * | 2013-10-30 | 2014-02-05 | 无锡思泰迪半导体有限公司 | Preprocessing method for images before digital-to-analogue conversion and structure thereof |
| CN109557995A (en) * | 2018-11-21 | 2019-04-02 | Tcl移动通信科技（宁波）有限公司 | A kind of application program interrupt control method, mobile terminal and storage medium |
-
2013
- 2013-10-30 CN CN201320675239.XU patent/CN203590206U/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103560793A (en) * | 2013-10-30 | 2014-02-05 | 无锡思泰迪半导体有限公司 | Preprocessing method for images before digital-to-analogue conversion and structure thereof |
| CN109557995A (en) * | 2018-11-21 | 2019-04-02 | Tcl移动通信科技（宁波）有限公司 | A kind of application program interrupt control method, mobile terminal and storage medium |
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Effective date of registration: 20221221 Address after: No. 16, Changjiang Road, Xinwu District, Hangzhou, Zhejiang 310000 Patentee after: Hangzhou Sitai Microelectronics Co.,Ltd. Address before: No. 16, Changjiang Road, New District, Wuxi City, Jiangsu Province, 214028 Patentee before: STEADICHIPS Inc. |
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Granted publication date: 20140507 |