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自己試著翻譯了一個(gè)三電平同步脈沖的短文，請(qǐng)大家指正！ |
| 作者：ywm2008ic 欄目：數(shù)字廣電 |
為什么HDTV使用三電平同步？ 作者：Dave Pincek The advent of HDTV has brought a NUMBER of new concepts and TECHNOLOGIES with it. One of the concepts put into practice is tri-level sync. Tri-level sync solves some traditional problems found with bi-level sync. Although tri-level sync is preferable with the new television SYSTEM, we still find ourselves interfacing to SYSTEMs capable of HANDLING ONLY bi-level sync. Therefore, the need exists to convert from tri-level to bi-level sync on occasion. This Tech Corner will acquaint the reader with the new tri-level sync format and its relationship to bi-level sync. HDTV的到來也帶來了許多新的概念和技術(shù)，其中之一就是三電平同步。三電平同步解決了一些過去在雙電平同步時(shí)出現(xiàn)的問題。盡管三電平同步在新的電視系統(tǒng)中使用較多，我們發(fā)現(xiàn)仍然需要同時(shí)考慮那些僅使用雙電平同步的系統(tǒng)。所以，有時(shí)候需要把三電平的同步信號(hào)轉(zhuǎn)換為雙電平的同步信號(hào)。這份“技術(shù)角”將要使讀者了解三電平的同步信號(hào)格式以及它與雙電平的同步信號(hào)的關(guān)系。 Bi-Level Sync Bi-level sync has been the STANDARD synchronization signaling method for all forms of VIDEO including COMPUTER VIDEO, composite VIDEO, S-VIDEO, and component VIDEO. Bi-level refers to two levels. For sync, this means a PULSE having two voltage levels (a high and low level, relatively speaking), hence the NAME. Systems using bi-level sync are edge triggered. Typically, the negative-going, leading edge of the PULSE triggers the synchronization PROCESS (Figure 1). DISPLAY SYSTEMs must "look" for this negative going edge in order to identify the moment in time when to re-sync the raster scan PROCESS. Most will recall that COMPUTER graphic cards sometimes OUTPUT positive-going sync. Positive-going sync signal the DISPLAY that the graphics LINE rate has changed to a new format. 對(duì)于幾乎所有格式的視頻信號(hào)（如計(jì)算機(jī)輸出的視頻信號(hào)、復(fù)合視頻、S端子視頻和分量視頻）來說，雙電平同步已經(jīng)成為了一個(gè)標(biāo)準(zhǔn)的同步信號(hào)格式。雙電平指的就是兩個(gè)電平，對(duì)于同步信號(hào)來說，顧名思義，這意味著一個(gè)脈沖包含了兩個(gè)電平值（相對(duì)而言，就是一個(gè)高電平和一個(gè)低電平）。系統(tǒng)中使用的雙同步電平是沿觸發(fā)的。一般來講，負(fù)極性的、沿觸發(fā)的脈沖信號(hào)會(huì)觸發(fā)一個(gè)同步過程（如圖1）。顯示系統(tǒng)必須“找到”這個(gè)負(fù)極性的下降沿，以便確定重新同步光柵掃描進(jìn)程的時(shí)刻。更多時(shí)候還需要計(jì)算機(jī)顯卡產(chǎn)生一個(gè)正極性觸發(fā)的同步信號(hào)，它會(huì)通知顯示終端所顯示的圖像行頻已經(jīng)改變到一個(gè)新的格式了。 Looking for the sync PULSE has always been one of the "trickiest" of tasks for the DISPLAY signal PROCESSor. It requires careful biasing of the sync PROCESSing circuitry so that the sync PULSE is made as distinguishable as possible from the other voltage levels within the VIDEO signal. As PART of the VIDEO signal, bi-level sync introduces an unwanted DC component (Figure 2). In PROCESSing of composite, S-VIDEO, or component VIDEO the DC component is not too troublesome and can easily be managed as PART of the normal sync separation routine. When bi-level sync is introduced onto RGB VIDEO channels, the PROCESS is more complex. In some SYSTEMs, sync is introduced on the GREEN channel ONLY. This requires that the sync separation PROCESS be ultra clean; in most cases, however, it is not. Usually a very narrow sync PULSE remains. 對(duì)于顯示信號(hào)處理器來說，尋找同步脈沖一直都是一項(xiàng)十分重要的工作。為了能夠方便的將同步脈沖從包含著許多其他電平分量的視頻信號(hào)中區(qū)分出來，需要仔細(xì)設(shè)計(jì)同步信號(hào)處理電路。作為視頻信號(hào)的一部分，雙電平同步包含了一部分并不需要的直流分量（如圖2）。在對(duì)復(fù)合視頻信號(hào)、S端子信號(hào)或者是分量信號(hào)的處理過程中，直流分量并非難以處理，它能夠在通常的同步分離過程中被進(jìn)行處理掉。當(dāng)雙電平同步被引入RGB視頻信號(hào)通道后，處理過程就變得復(fù)雜了。在一些系統(tǒng)中，同步信號(hào)只是疊加在綠色通道上面，這就要求同步分離電路相當(dāng)出色，但在大多情況下其實(shí)并不如意。通常只會(huì)有較窄的同步脈沖被分離出來。 Residual sync results from incomplete removal of the sync information from a VIDEO PROCESSing channel. Sync is typically imposed on the GREEN channel in RGsB SYSTEMs. High definition component VIDEO signals contain sync on each channel.!Depending on the performance characteristics of the DC restoration circuitry within the VIDEO PROCESSing channel, some or all of the sync PULSE may not be removed from the GREEN channel. Residual sync causes the GREEN channel to bias incorrectly with respect to red and BLUE at the DISPLAY CRT, thus causing a color shift. Even in RGB SYSTEMs where sync is introduced on all three channels, there is some difficulty with maintaining consistent PROCESSing between the three channels. Again, small DC shifts in the black level caused by residual sync can disturb the color balance or gains of the VIDEO channels. 剩下的同步信息均是來源于視頻處理通道的不完整的同步信息。同步信息通常附加在RGsB系統(tǒng)中的綠色通道中。高分辨率的分量視頻信號(hào)在其每一個(gè)通道中都包含了同步信息！根據(jù)視頻處理通道中的直流電平恢復(fù)電路的性能，部分或全部的同步脈沖不會(huì)從綠色通道中移除。剩余的同步信息將使綠色通道無法與CRT顯示所需的紅色和藍(lán)色通道相匹配，因而會(huì)導(dǎo)致色偏。即使在RGB系統(tǒng)中三個(gè)通道中都有同步信息，在保持三個(gè)通道處理的一致時(shí)仍會(huì)有一些困難。同樣，由于殘留的同步信號(hào)而導(dǎo)致的黑電平上很小的直流偏移依然能夠影響顏色的平衡和各個(gè)視頻通道的增益。 A significant amount of POWER is used by the broadcast transmitter to send the sync PULSE. Polarity of the VIDEO signal is designed to minimize the amount of POWER used to transmit sync. And, while we have not transmitted ANALOG versions of high definition television terrestrially, early testing done during HDTV development demonstrated a need to improve the management of synchronization in the new television SYSTEM. Tri-level sync eliminates the DC component and provides a more robust way to identify the coming of synchronization in the signal chain. 由于大量的功率被廣播發(fā)射機(jī)用來發(fā)送同步脈沖，一般將視頻信號(hào)的極性設(shè)計(jì)為在傳送同步信號(hào)降低功耗的方式。同時(shí)，我們?cè)诘孛鎻V播中到目前也沒有傳送高清電視信號(hào)的版本。早期在HDTV開發(fā)中完成的測(cè)試證明，在新的電視系統(tǒng)中需要改進(jìn)同步信號(hào)的處理方式。三電平同步方式消除了直流分量，提供了更有效的辦法來確定同步信號(hào)在信號(hào)鏈的位置。 Tri-Level Sync Tri-level sync was introduced with the SMPTE 240 ANALOG HDTV STANDARD. Previous to that, the early HDTV 1125/60 SYSTEMs used various synchronization waveforms, as provided by various 1125/60 EQUIPMENT manufacturers. The creators of the later SMPTE 240 HDTV STANDARD searched for a STANDARD sync waveform that would ensure SYSTEM compatibility. The goal was to provide more precise synchronization and relative timing of the three component VIDEO signals. HDTV component VIDEO has sync present on all three channels: Y, Pb, and Pr. In addition, the sync structure needs to be resilient enough to endure multigenerational recording and other noisy situations. Tri-level sync met the requirements. 在模擬高清晰度電視標(biāo)準(zhǔn)SMPTE240中引入了三電平同步。在過去，由于眾多不同的1125/60儀器制造商的出現(xiàn)，早期的HDTV 1125/60系統(tǒng)使用了很多中同步波形。后來SMPTE 240 HDTV標(biāo)準(zhǔn)的出現(xiàn)確立了一個(gè)標(biāo)準(zhǔn)的同步信號(hào)波形，確保了系統(tǒng)的兼容性。目標(biāo)是提供更為精確的同步信息及相關(guān)的三個(gè)分量視頻信號(hào)的時(shí)序。HDTV分量視頻信號(hào)的Y、Pb、Pr三個(gè)通道中均有同步信號(hào)。同時(shí)，同步信號(hào)的構(gòu)成方式需要足夠可靠有效并承受持續(xù)長(zhǎng)期的充滿噪聲的環(huán)境。三電平同步正好滿足了這個(gè)要求。 Figure 3 shows a graphic representation of a tri-level sync signal. As defined by the SMPTE 240 STANDARD, the PULSE will start at the |
| 2樓： | >>參與討論 | ||
| 作者： iC921 于 2006/3/11 2:50:00 發(fā)布：
Tri-Level Sync in a Bi-Level World Tri-Level Sync in a Bi-Level Worldby Dave Pincek, Vice President of PRODUCT Development The advent of HDTV has brought a NUMBER of new concepts and TECHNOLOGIES with it. One of the concepts put into practice is tri-level sync. Tri-level sync solves some traditional problems found with bi-level sync. Although tri-level sync is preferable with the new television SYSTEM, we still find ourselves interfacing to SYSTEMs capable of HANDLING ONLY bi-level sync. Therefore, the need exists to convert from tri-level to bi-level sync on occasion. This Tech Corner will acquaint the reader with the new tri-level sync format and its relationship to bi-level sync. Bi-Level SyncBi-level sync has been the STANDARD synchronization signaling method for all forms of VIDEO including COMPUTER VIDEO, composite VIDEO, S-VIDEO, and component VIDEO. Bi-level refers to two levels. For sync, this means a PULSE having two voltage levels (a high and low level, relatively speaking), hence the NAME. Systems using bi-level sync are edge triggered. Typically, the negative-going, leading edge of the PULSE triggers the synchronization PROCESS (Figure 1). DISPLAY SYSTEMs must "look" for this negative going edge in order to identify the moment in time when to re-sync the raster scan PROCESS. Most will recall that COMPUTER graphic cards sometimes OUTPUT positive-going sync. Positive-going sync signal the DISPLAY that the graphics LINE rate has changed to a new format.Looking for the sync PULSE has always been one of the "trickiest" of tasks for the DISPLAY signal PROCESSor. It requires careful biasing of the sync PROCESSing circuitry so that the sync PULSE is made as distinguishable as possible from the other voltage levels within the VIDEO signal. As PART of the VIDEO signal, bi-level sync introduces an unwanted DC component (Figure 2). In PROCESSing of composite, S-VIDEO, or component VIDEO the DC component is not too troublesome and can easily be managed as PART of the normal sync separation routine. When bi-level sync is introduced onto RGB VIDEO channels, the PROCESS is more complex. In some SYSTEMs, sync is introduced on the GREEN channel ONLY. This requires that the sync separation PROCESS be ultra clean; in most cases, however, it is not. Usually a very narrow sync PULSE remains.
Residual sync results from incomplete removal of the sync information from a VIDEO PROCESSing channel. Sync is typically imposed on the GREEN channel in RGsB SYSTEMs. High definition component VIDEO signals contain sync on each channel. Depending on the performance characteristics of the DC restoration circuitry within the VIDEO PROCESSing channel, some or all of the sync PULSE may not be removed from the GREEN channel. Residual sync causes the GREEN channel to bias incorrectly with respect to red and BLUE at the DISPLAY CRT, thus causing a color shift. Even in RGB SYSTEMs where sync is introduced on all three channels, there is some difficulty with maintaining consistent PROCESSing between the three channels. Again, small DC shifts in the black level caused by residual sync can disturb the color balance or gains of the VIDEO channels. A significant amount of POWER is used by the broadcast transmitter to send the sync PULSE. Polarity of the VIDEO signal is designed to minimize the amount of POWER used to transmit sync. And, while we have not transmitted ANALOG versions of high definition television terrestrially, early testing done during HDTV development demonstrated a need to improve the management of synchronization in the new television SYSTEM. Tri-level sync eliminates the DC component and provides a more robust way to identify the coming of synchronization in the signal chain. Tri-Level SyncTri-level sync was introduced with the SMPTE 240 ANALOG HDTV STANDARD. Previous to that, the early HDTV 1125/60 SYSTEMs used various synchronization waveforms, as provided by various 1125/60 EQUIPMENT manufacturers. The creators of the later SMPTE 240 HDTV STANDARD searched for a STANDARD sync waveform that would ensure SYSTEM compatibility. The goal was to provide more precise synchronization and relative timing of the three component VIDEO signals. HDTV component VIDEO has sync present on all three channels: Y, Pb, and Pr. In addition, the sync structure needs to be resilient enough to endure multigenerational recording and other noisy situations. Tri-level sync met the requirements.
Figure 3 shows a graphic representation of a tri-level sync signal. As defined by the SMPTE 240 STANDARD, the PULSE will start at the zero volts (specified black level) and first transitions negative, to -300 mV (+/- 6 mV). After a specified period, it transitions positive + 300 mV (+/- 6 mV), holds for a specified period and then returns to zero or black level. The DISPLAY SYSTEM "looks" for the zero crossing of the sync PULSE. Each half of the tri-level sync PULSE is defined to be 44 samples (reference clock periods) wide, for a total sync PULSE width of 88 samples. The rise time is defined to be four samples wide +/- 1.5 samples. This symmetry of design results in a net DC VALUE of zero volts. This is one major advantage of tri-level sync. This solves the problem of a bi-level signal introducing a DC component into the VIDEO signal. The elimination of DC offset makes signal PROCESSing easier. Within our new DIGITAL television SYSTEM, the unique excursions of the sync derive numerical VALUEs that are easily coded and easily recognized within the DIGITAL transmission channel. Converting Tri-Level to Bi-Level SyncThere are times when it is necessary to convert tri-level sync to bi-level sync such as when component HDTV is converted to RGBHV. A format converter, like Extron's CVC 200, will perform the conversion of tri-level to bi-level sync as PART of the component HDTV to RGB conversion PROCESS. Traditional DISPLAYs and projectors not capable of HANDLING tri-level sync will "see" sync information in the traditional way.Any time signals are converted from one format to another, the relative timing of the conversion is of prime importance. The introduction of timing error, once introduced into a signal channel, is difficult to REPAIR. The positioning of tri-level sync with respect to active VIDEO and the wider excursion from peak negative (-300 mV) to peak positive (+300 mV) provided by this format establishes easier sync detection and more consistent triggering through the use of the zero crossing. When converting bi-level sync, the leading edge of the bi-level PULSE should be aligned using the zero crossing of the tri-level sync. By doing so, the bi-level sync PULSE will provide leading-edge trigger at the proper point and correct timing will be maintained. Figure 4 shows the relationship of a tri-level sync signal to a properly-timed bi-level sync signal. Anyone involved in interfacing VIDEO signals will, at some point, encounter the need to convert tri-level sync to bi-level sync. As time progresses, a growing GROUP of DISPLAYs and projectors will be designed to cope directly with these format differences. In the meantime, technicians should be aware of the differences in sync construction and the proper timing relationship for conversion between these two common formats. |
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| 3樓： | >>參與討論 |
| 作者： iC921 于 2006/3/11 3:06:00 發(fā)布：
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| 4樓： | >>參與討論 |
| 作者： ywm2008ic 于 2006/3/13 22:05:00 發(fā)布：
謝謝ic921 對(duì)，就是這篇文章，我看了覺得還是有點(diǎn)收獲，所以一時(shí)興起就試著翻了一下�？上Ш竺鎴D沒貼上去，遺憾遺憾。 倒是謝謝ic921幫了我這個(gè)忙了。 ：） |
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| 5樓： | >>參與討論 |
| 作者： iC921 于 2006/3/13 23:15:00 發(fā)布：
不用謝 我也是看了沒圖就把它找出來的。 我不知道GOOLE翻譯在哪了，回來找一下。有興趣到模擬多多參與我們的翻譯。 |
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