茶馆 ： 所有"无关紧要的"话题

Off topic: 茶馆 ： 所有"无关紧要的"话题

wherestip
United States
Local time: 21:49
Chinese to English
+ ...
 Multiples of the system clock Feb 21, 2008

Wenjer Leuschel wrote:

Steve,

No, I am not translating anything like that. I just want to know what if a system clock is composed of an oscillator and the same oscillator with two outputs 90° out of phase to have sine and cosine combined at the same time. The idea is, sine and cosine would cancell each other at 90° and 270° and thus produce a distinct drop at those points, while during other times, the oscillation is either "high" or "low." The precision is a problem, I know.

- Wenjer

Wenjer,

Yes, to produce an exact 90 degree phase shift could be a challenge. In addition, the lack of a multiplier relationship to the reference clock could also be problematic. The rising and falling edges won't exactly be at the 1/4 and 3/4 points of the sine wave. They are actually a bit more to the left. Don't quote me, but I think they are at the 1/8 and 5/8 points of the sine wave.

It's good to have a multiplier relationship between the system clock and the reference clock, especially if any other multiples of the system clock is needed, for example a 2x system clock or a 4x system clock. They then can all be generated using the same PLL.

[Edited at 2008-02-21 02:33]

Wenjer Leuschel
Taiwan
Local time: 10:49
English to Chinese
+ ...
 The falling edge Feb 21, 2008

wherestip wrote:

Wenjer,

Yes, to produce an exact 90 degree phase shift could be a challenge. In addition, the lack of a multiplier relationship to the reference clock could also be problematic. The rising and falling edges won't exactly be at the 1/4 and 3/4 points of the sine wave. They are actually a bit more to the left. Don't quote me, but I think they are at the 1/8 and 5/8 points of the sine wave.

It's good to have a multiplier relationship between the system clock and the reference clock, especially if any other multiples of the system clock is needed, for example a 2x system clock or a 4x system clock. They then can all be generated using the same PLL.

Steve,

I can see the reason why we need a muliplier relationship between the system clock and the reference clock. If we want to invert a 2x system clock and divide it then for a 90° shift to the left, we need the relationship.

However, the sine and the cosine waves cross at 1/8 to maintain "high" until they reach 1/4 of the cycle to sum up to zero and falls to "low" immediately after. From the falling edge at 1/4 on, it must stay at "low" even when both waves cross at 5/8 of the cycle. When they reach 3/4, the sum rises to zero and jumps to "high" immediately after. This is easily calculated by definition of sine and cosine. But we know that there isn't such "idealistic" waves in the reality to sum up to be an "idealistic" clock as such. So, there must be some clocking between 3/16 and 5/16 as well as between 11/16 and 13/16 to ensure the reading of "high" and "low."

I know it isn't easy to realize such a system clock, the more difficult the higher frequency is. But, what I wanted to know is if it is possible theoretically. Purely mathematically, the sum of a sine and a cosine do make such distinct falls and rises, doesn't it? Or else, a sine wave is already good enough to serve as a system clock, isn't it?

I appreciate your hint to PLL for possible realization of a cosine wave with the one and the same oscillator. At least it confirms my supposition of the possibility of having a system clock with the sum of sine and cosine. A lot of trouble, I know, but it's possible to achieve such a "discrete timing" as I presumed.

- Wenjer

P.S. Here I got one sine/cosine wave oscillator.
http://www.interq.or.jp/japan/se-inoue/e_ckt20.htm
However, it is in low frequency. I guess, it must be quite difficult in high frequency.

[Edited at 2008-02-21 06:46]

wherestip
United States
Local time: 21:49
Chinese to English
+ ...
 Reference Clock Feb 21, 2008

Wenjer,

Theoretically, yes. You can sum a sine wave and a cosine wave to achieve a bigger amplitude in the waveform, and therefore also achieve a more dramatic rise and fall.

There are also some other considerations in maintaining the synchronicity between the reference clock and the system clock. For example, a microprocessor is typically fed by a lower frequency reference clock generated on the system board. Typically one would want to synchronize the system clock used by the microprocessor to that used by the other system control chips on the board as much as possible. Of course, with today's high speed devices, that sometimes becomes a challenge.

[Edited at 2008-02-21 14:15]

Wenjer Leuschel
Taiwan
Local time: 10:49
English to Chinese
+ ...
 Glad to be out Feb 21, 2008

To tell you the truth, Steve, I am glad that I am out of that field since decades. Or else, I would have headaches to cope with the high frequencies and high speeds of nowadays.

xxxchance
French to Chinese
+ ...
TOPIC STARTER
 老孙： Feb 26, 2008

ysun
United States
Local time: 21:49
English to Chinese
+ ...
 能劝阻就尽量劝阻 Feb 26, 2008

chance,

[Edited at 2008-02-26 16:52]

xxxchance
French to Chinese
+ ...
TOPIC STARTER
 明白，谢谢！ Feb 26, 2008

Yueyin Sun wrote:

chance,

[Edited at 2008-02-26 16:52]

ysun
United States
Local time: 21:49
English to Chinese
+ ...
 我思想比较保守 Feb 26, 2008

chance wrote:

http://shop.vegas.com/shows/showtimes2.jsp?show=40

xxxchance
French to Chinese
+ ...
TOPIC STARTER
 对，我指的也是这类 Feb 26, 2008

Yueyin Sun wrote:

chance wrote:

http://shop.vegas.com/shows/showtimes2.jsp?show=40

ysun
United States
Local time: 21:49
English to Chinese
+ ...
 我觉得 Jubilee 这种 show 不能算黄色 Feb 26, 2008

chance wrote:

[Edited at 2008-02-27 00:37]

ysun
United States
Local time: 21:49
English to Chinese
+ ...
 不老实的人总会栽跟头 Feb 26, 2008

jyuan_us
United States
Local time: 22:49
Member (2005)
English to Chinese
+ ...
 英达夸自己老婆的一句话挺逗的 Feb 26, 2008

jyuan_us
United States
Local time: 22:49
Member (2005)
English to Chinese
+ ...
 我朋友她爸为团长的一个团 Feb 26, 2008

Yueyin Sun wrote:

chance,

[Edited at 2008-02-26 16:52]

[Edited at 2008-02-26 21:31]

[Edited at 2008-02-26 21:32]

xxxchance
French to Chinese
+ ...
TOPIC STARTER
 不知我们这里有没有会打高球的？ Feb 26, 2008

[Edited at 2008-02-27 00:13]

ysun
United States
Local time: 21:49
English to Chinese
+ ...
 年代不同了 Feb 27, 2008

jyuan_us wrote:

80年代，天津某大公司有个团去日本。日方替他们付了旅馆费，然后把发票给他们回国报销。于是，他们就用这笔钱每人买了台彩电。回国后风声走漏，团长被判一年徒刑。要是搁现在，这点事算什么？那团长是搞技术出身的副总经理、引进项目现场总代表。外方总代表不知他为何突然消失。新任总代表说他病了。外方总代表就说，那就等他病好了再谈，你不懂，我跟你讲不清！没想到那前任总代表的病假比产假还长得多。:D

80年代在国内工作时，哪怕出国就是为了出席一天的国际会议，也得接受3天外事教育。从宣读文件一直到告诉你喝汤不准发出声。像拉斯维加斯、大西洋赌城、自由女神像这些地方按规定都是不准去的，日本东京新宿的歌舞伎町、靖国神社也是不准去的。如果去莫斯科开一天的会，3天外事教育，去时坐一星期的火车，回来也是一星期的火车。这种会还不如不参加。

http://zh.wikipedia.org/wiki/歌舞伎町

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茶馆 ： 所有"无关紧要的"话题

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