| 主题：高速信号路径的设计问题 -- DVI/HDMI 电缆延长方案的挑战 |
| 在线问答： |
| [问：hkunming0668] |
1.目前优质DVI/HDMI 电缆最长可达几米?
2.对电缆的量测有哪些量测项目?
3.对电缆的量测有哪些解决方案 |
| [答：Benwang] |
DVI/HDMI通过DVI/HDMI电缆传输的距离一般在5米以内. |
[2007-7-24 10:43:39] |
| [主持人：ChinaECNet] |
各位听众（网友），上午好！欢迎参加中电网在线座谈。今天，我们有幸邀请到美国国家半导体公司的专家就“高速信号路径的设计问题 -- DVI/HDMI 电缆延长方案的挑战”举行在线座谈。在座谈中，您可就您关心的问题与美国国家半导体公司的专家在线进行直接、实时的对话交流。中电网衷心希望通过大家的共同努力，不仅能够增进各位听众（网友）对“高速信号路径的设计问题 -- DVI/HDMI 电缆延长方案的挑战”的了解和掌握，而且能够为大家事业的发展带来裨益。 |
[2007-7-24 10:46:15] |
| [问：percy_wang@ali.com.tw] |
如何控制PCB的布线阻抗？根据经验而言，需要考虑的重点有哪些？ |
| [答：Robertshen] |
主要是线型，如微带线、夹心线等。具体可以参看有关文献计算。 |
[2007-7-24 10:46:23] |
| [问：Genius_XL] |
HDMI电缆这么大的带宽，我想问一下它的信号干扰问题是怎么解决的？ |
| [答：Noelfung] |
usually the core will be shielded to reduce crosstalk or interference |
[2007-7-24 10:46:44] |
| [问：wangchen] |
1 美国国家半导体关于DVI/HDMI领域最新发展的技术都有哪些？与其它公司相比有何优势？
2 关于DVI/HDMI领域最新发展的技术的主要应用？ |
| [答：Benwang] |
国半在高速数据传输方面技术领先, 这些技术也可以应用于DVI/HDMI领域. 主要的优势包括: 高速(3.4Gbps HDMI V1.3), 可靠(8KV ESD), 低功耗, 小封装. |
[2007-7-24 10:48:01] |
| [问：huatingxp] |
请问能不能介绍一下，各种差分信号（LVDS、CML及LVPECL等）的电平标准，以及在实际应用中以上差分电平支持的最高传输速率为多少？ |
| [答：Stevenfeng] |
LVDS:350mV 3Gbps
CML:800mV 10Gbps
LVPECL:800mV 5Gbps |
[2007-7-24 10:48:40] |
| [主持人：ChinaECNet] |
我们已经进入问答阶段如果听众想重温演讲或内容可以点击下面“回顾演示”重看演讲。 |
[2007-7-24 10:48:45] |
| [问：wenjing62] |
HDMI几个规范有那些什么区别?是否向后兼容? |
| [答：Benwang] |
主要的区别是速率, HDMI v1.3支持 3.4Gbps 16-bit deep color. 支持向下兼容. |
[2007-7-24 10:50:11] |
| [问：wenjing62] |
和现有的模拟接口如复合、S-Video 和分量视频相比, HDMI的优点有哪些？ |
| [答：Robertshen] |
没有可比性。HDMI是数字高清信号标准。 |
[2007-7-24 10:50:53] |
| [问：Thomas Li] |
请教NS专家两个问题:
1.HDMI是否会被display port取代?或者是两者共存的局面?
2.HDMI电缆延长方案,目前NS有repeater的解决方案么? |
| [答：Noelfung] |
1. DisplayPort is still in the very preliminary stage while that HDMI is getting popular in both AV and PC market. I think, in the near future, HDMI will dominate the market.
2. As of today, we only have EQ. |
[2007-7-24 10:51:01] |
| [问：peng_peng] |
通常我们对DVI信号，是采用严格参考地平面来设计的。为了尽量减少其他信号对DVI信号的干扰，我们至少应该保持其他信号距离DVI信号多少距离才合适？ |
| [答：Noelfung] |
Remember that there is parameter called "s" in the pcb layout section? "s" is the separation between the differential pair. We usually place adjacent differential pair at least 2s away. Place TTL signals at least 3s away. |
[2007-7-24 10:54:16] |
| [问：ys3663391] |
针对不同的电缆，是不是也有不同的方案，还是在一定范围内方案都能适用 |
| [答：Benwang] |
可以这样说, 例如, DS16EV5110 可以用在HDMI/DVI电缆和CAT5网线应用中. |
[2007-7-24 10:54:27] |
| [问：cake_king] |
如果两条线迹长度不同，有什么方法可以调整？ |
| [答：Robertshen] |
如果是PCB布线的话，通过弯线来增加短线的长度，使之尽量相等。 |
[2007-7-24 10:55:33] |
| [问：zjlicool] |
差分信号布线,两边需要加地线保护吗? |
| [答：Benwang] |
根据不同的应用可能不同, 具体可以参考国半"LVDS用户手册". |
[2007-7-24 10:56:38] |
| [问：creative520] |
各位专家好，我想问一下LVDS中的CDR问题，目前常用的CDR方法有那些？其优缺点有那些？对1G以上的LVDS信号其中的CDR关键问题是什么？ |
| [答：Noelfung] |
CDR is a difficult yet important issue in LVDS. There are several topologies to implement CDR, analog or digital. I don"t want to go over this topic in this seminar because it will take quite a long page to describe. Basically, the key element in CDR is the PLL. |
[2007-7-24 10:57:37] |
| [主持人：ChinaECNet] |
各位观众，现在用户提问很踊跃，专家正在逐一回答。请耐心等待您问题的答案，同一问题请不要多次提交。 |
[2007-7-24 10:59:01] |
| [问：zjlicool] |
两层板如何控制差分阻抗? |
| [答：Robertshen] |
在一面平行布线，调整线的间距和线宽。 |
[2007-7-24 11:00:27] |
| [问：wyp791223] |
HDMI 支持哪种类型的视频？ |
| [答：Benwang] |
HDMI支持几乎所有的数字视频和数字音频. 例如: 1080P/1080i/720P 等等. |
[2007-7-24 11:00:58] |
| [问：zhouyu0779] |
如何減低供電線路所產生的噪音? |
| [答：Stevenfeng] |
选用较好DC/DC的转换器， 或好的低压降稳压器。例如：LM3674,LM1770,LM25576,LP38691. |
[2007-7-24 11:01:06] |
| [问：yujie1104] |
请问贵公司有没有有源的cable 延长方案？如何解决其供电的问题？ |
| [答：JanetWu] |
National Semiconductor has released a Video Equalizer for DVI, HDMI, and CAT5 Cables DS16EV5110 which can extend cable. Please go to our website for more information. |
[2007-7-24 11:01:14] |
| [问：xl_cumt] |
PCB良好的设计如何做到好的S/N，如果采用双面板，能否做到好的抗干扰能力，再怎么说PCB板也只是在2维空间，对于三维空间的干扰，怎样处理？ |
| [答：Noelfung] |
We didn"t show the principle of microstrip line in the presentation. Basically, a transmission line on top of a "large" ground plane would confine the E-field of the transmission line within the dielectric of the pcb. As a result, the EMI or RF emission will be reduced. It would be easiler to understand if we could show you a picture, unfortunately, this on-line section doesn"t allow us to do so. |
[2007-7-24 11:03:13] |
| [问：callancc] |
用什么线传输LVDS信号(1G)，和电路板的联接采用什么样的端口？需要注意些什么？ |
| [答：Benwang] |
标准中没有规定LVDS的传输媒介, 可以是用CAT5, PCIe或专用线, 等等. 也没有规定具体的接口. |
[2007-7-24 11:04:03] |
| [问：zjlicool] |
DVI/HDMI 电缆/插座认证机构有哪些? |
| [答：Stevenfeng] |
ATC认证机构。 |
[2007-7-24 11:05:11] |
| [问：ys3663391] |
在设计中如何平衡传输速度和损耗，有什么经验可以分享？ |
| [答：Noelfung] |
That depends on the transmission media. If the media is pcb, use low loss dielectric material and thicker copper cladding. If the media is cable, of course, you have to use high quality cable. For example, low loss, low crosstalk, low skew, shielded cable. |
[2007-7-24 11:05:58] |
| [问：zhouyu0779] |
在HDMI中如何加強信號路徑的性能? |
| [答：Robertshen] |
补偿方法，如加重/去加重、均衡等来提升信号的质量。 |
[2007-7-24 11:07:28] |
| [问：callancc] |
800Mbps的串行信号，采用LVDS方式传输的话，比较保险的传输距离最长多远？是12米么？ |
| [答：Noelfung] |
This is a very typical question we got everyday. The answer is, that"s depend. For example, what type of cable you are using? In addition, if you have pre-emphasis or EQ, that will be another story. In addition, whether your data is DC-balanced or not will also affect the overall performance. |
[2007-7-24 11:08:26] |
| [问：ylz8690@yahoo.com.cn] |
电缆延长主要还是靠信号中继吗? |
| [答：Robertshen] |
中继是一个方法，也可以采用其它方法，如提高电缆的质量，提升信号的质量。 |
[2007-7-24 11:09:55] |
| [问：ylq661] |
不同的电缆损耗不一样,预加重也不一样,在应用上如何进行预加重? |
| [答：Benwang] |
可以用带可调预加重的器件. |
[2007-7-24 11:11:28] |
| [问：callancc] |
我注意到一些芯片的管脚支持LVDS方式传输，并且输出电压2.5伏，请问这是业内的标准么？请问输出电压有更高些的么？ |
| [答：Noelfung] |
Usually, the common mode voltage of LVDS is 1.2V while that CML is 2.5V. LVDS is a standard while that CML is not. Since CML is not a standard, AC coupling is usually adopted |
[2007-7-24 11:14:47] |
| [问：keenron] |
阻抗断层的加重会不会加剧系统抖动,应如何减少这种回波带来的噪声影响呢?谢谢! |
| [答：Benwang] |
您指的是阻抗匹配问题吗? 阻抗不匹配是抖动的主要原因, 因尽量做到阻抗匹配. |
[2007-7-24 11:15:47] |
| [问：hunterzw] |
采用LVDS芯片，再加上预加重功能的支持，高频增益增幅能达到多少？ |
| [答：Noelfung] |
Typical gain is 3dB to 6dB |
[2007-7-24 11:16:38] |
| [问：huamuzi12@etang.com] |
交流耦合及互操作性问题该如何解决? |
| [答：Benwang] |
如果是不同的电平, 应使用AC偶合的方式. |
[2007-7-24 11:16:53] |
| [问：yujie1104] |
请问专家 DS38EP100的工作原理是什么？如何做到无源补偿？ |
| [答：Noelfung] |
Actually, an EQ is a high pass filter. So it doesn"t matter whether it is active or passive. |
[2007-7-24 11:17:41] |
| [问：huijie] |
无源均衡器和有源均衡器在使用上有什么优缺点? |
| [答：Benwang] |
有源EQ可以放大信号, 无源EQ对信号有衰减.
有源EQ需要耗电, 无源EQ不需要电源.
|
[2007-7-24 11:18:46] |
| [问：xiaobibi1984] |
请专家解释,重复计时器是如何保证接收时钟和发送时钟同步? |
| [答：Noelfung] |
There is a PLL inside a reclocker, so the PLL will lock to the incoming data and thus synchronized. |
[2007-7-24 11:19:37] |
| [问：jimlee0924] |
什么是UI?它代表多少时间? |
| [答：Benwang] |
UI代表Unit Interval, 即单位比特的时间. |
[2007-7-24 11:19:46] |
| [问：liyong98847] |
“标准”HDMI 电缆和“高速”电缆之间有何不同？ |
| [答：Robertshen] |
主要是要符合HDMI的标准。见讲演资料的25页 |
[2007-7-24 11:20:28] |
| [问：zhouyu0779] |
National產品中是否有带可调预加重的器件? |
| [答：Benwang] |
有, 例如DS25BR100系列, 等等. |
[2007-7-24 11:20:43] |
| [问：yujie1104] |
DS16EV5110可以用于不带独立电源的repeater设计吗？如何解决它的供电问题？ |
| [答：Benwang] |
可以, 可以用电缆供电. |
[2007-7-24 11:21:32] |
| [问：djwlwxl] |
如何确定均衡器的补偿度?它和那些因素有关? |
| [答：Noelfung] |
For adaptive EQ, the feedback system inside the EQ will determine the appropriate compensation. For settable EQ, the user can adjust the compensation by looking at the eye diagram coming out from the EQ or it could be determined by the system BER. |
[2007-7-24 11:22:49] |
| [问：scale_xie] |
HDMI 相对于现有的模拟视频接口如复合、S-Video 和分量视频的优点有哪些？ |
| [答：Robertshen] |
HDMI是数字高清标准。与模拟视频信号没有可比性。 |
[2007-7-24 11:23:07] |
| [问：huatingxp] |
lvds信号传输，在做为输出，和输入时，有没有什么不同？ |
| [答：Benwang] |
电平标准一样, 但匹配不同. |
[2007-7-24 11:23:07] |
| [问：zhouyu0779] |
如何解決電壓漂移時產生能量輻射,從而導致EMI的問題? |
| [答：JanetWu] |
Balanced cables (twisted pair) are usually better than unbalanced cables (ribbon cable, multi-conductor) for noise reduction and signal quality. Balanced cables tend to generate less EMI due to field canceling effects. They also tend to pick up electromagnetic radiation as common-mode (not differential-mode) noise, which is rejected by the receiver.
|
[2007-7-24 11:23:45] |
| [问：zjlicool] |
差分信号阻抗匹配电阻一般加在那一端比较好?(源端/负载端只允许加一个) |
| [答：Benwang] |
LVDS信号在负载端加匹配. |
[2007-7-24 11:24:19] |
| [主持人：ChinaECNet] |
各位观众，现在用户提问很踊跃，专家正在逐一回答。请耐心等待您问题的答案，同一问题请不要多次提交。 |
[2007-7-24 11:24:48] |
| [问：szcharle] |
HDMI支持哪种类型的视频？ |
| [答：Andrewchiu] |
HDMI支持几乎所有的数字视频和数字音频. 例如: 1080P/1080i/720P 等等. |
[2007-7-24 11:26:29] |
| [问：keenron] |
关于走线.采用微带走线通孔相当串入电感,有好的办法改善其影响吗?是否可以通过电容匹配来补偿? |
| [答：Robertshen] |
首先尽量减少过孔。如果串入电感严重，可以通过增加电阻和电容网络来补偿。 |
[2007-7-24 11:27:06] |
| [问：peng_peng] |
如何选择DVI的connector？除了要求它具有较低的损耗外，还应该考虑哪些因素。谢谢！ |
| [答：Benwang] |
有标准的DVI接口, 选择满足标准的接口. |
[2007-7-24 11:27:47] |
| [问：sorryhaha] |
高速信号在传输时，怎么计算传输长度（带来电容、电感效应）对传输信号的影响？ |
| [答：Noelfung] |
That has to done by simulation. You got the simulation parameters from PCB vendor or cable manufacturer and then perform a simulation. This is the most accurate way to estimate. |
[2007-7-24 11:27:56] |
| [问：liyong98847] |
HDMI 向后兼容 DVI （数字视频接口）吗？ |
| [答：Benwang] |
是. |
[2007-7-24 11:29:51] |
| [问：Alice Hui] |
Is it possible to use CAT5 cable in HDMI v1.3 application? |
| [答：Andrewchiu] |
It is difficult but not impossible. CAT5 cable is cheap because it is not independently sealed, high skew, high loss and high cross talk. The problems get serious at high frequency. Even though you use a high quality CAT5 cable with excellent performance in the aforesaid parameters, you cannot overcome the cross talk appear in the RJ-45 connector. |
[2007-7-24 11:31:52] |
| [问：amatist] |
在可靠性要求高的场合，是否需要对接口进行相关的保护，如何对接口进行保护？ |
| [答：Benwang] |
是, 因为接口是最外的器件, 直接跟电缆相连. 可以选择具有更高ESD保护等级的器件, 以及外加独立保护器件. |
[2007-7-24 11:31:55] |
| [问：xiaobibi1984] |
LVDS和TMDS有什么区别？ |
| [答：Robertshen] |
TMDS是一类似CML信号。主要是电平的差别。 |
[2007-7-24 11:31:59] |
| [问：amatist] |
有的设计中，在差分数据通道中加入共模抑制器，是否有必要？ |
| [答：Stevenfeng] |
共模抑制器能更好的抑制共模干扰，根据系统要求确定。 |
[2007-7-24 11:32:20] |
| [问：peng_peng] |
如何通过信号完整性的仿真，来评估一个具有DVI Connector和DVI电缆的通道。 |
| [答：Noelfung] |
I guess Spice model is the commonly used model today. If you have the spice model of the connector and cable, you can perform a simulation and see whether the eye diagram is good or not. |
[2007-7-24 11:32:41] |
| [问：percy_wang@ali.com.tw] |
高频增益是否会导致EMI问题？ |
| [答：Robertshen] |
高频增益不会导致EMI。信号的幅度会导致EMI。 |
[2007-7-24 11:33:17] |
| [问：keenron] |
由于累积电荷(长时间高电平或低电平)引起的符号间干扰应该如何均衡?自适应吗? |
| [答：Noelfung] |
It would be difficult to compensate on the receiver side because some bits may have lost. You have to encode your TX data to DC-balanced type. For example, 8b/10b coding is one of the DC-balanced code. |
[2007-7-24 11:35:09] |
| [问：chyren] |
请问HDMI接口和SPDIF接口有什么区别？ |
| [答：Benwang] |
不同的标准, HDMI包括视/音频, SPDIF是音频标准. |
[2007-7-24 11:35:10] |
| [问：magic_2218] |
请问HDMI信号的布线的宽度和长度的最佳方案是什么? |
| [答：Robertshen] |
要看PCB的材质而定。计算阻抗匹配为最佳。 |
[2007-7-24 11:37:21] |
| [问：yangao] |
HDMI 支持 Dolby Digital、DTS 和高分辨率的音频格式吗？ |
| [答：Noelfung] |
Yes, expecailly HDMI v1.3. It supports the latest digital audio technology. |
[2007-7-24 11:37:37] |
| [问：move on] |
高速信号路径的设计将如何避免一些干扰问题？？ |
| [答：Benwang] |
遵守3S准则, 线对1S间距, 线对间2S, 差分与单端间3S. |
[2007-7-24 11:39:59] |
| [问：yjbs] |
HDMI电缆延长线能够延长到几米的距离，能否由一个源分出多路来传输 |
| [答：Stevenfeng] |
25米28AWG 1080P,20米CAT5 1080P.
点对点。 |
[2007-7-24 11:40:03] |
| [问：huamuzi12@etang.com] |
