硬件上是怎么实现的？ 4点几G赫兹的脉冲是怎么搞出来的？
内部RC电路跟外部时钟对齐？
问个真学术问题 CPU的内部时钟
版主： huangchong
Re: 问个真学术问题 CPU的内部时钟
外部时钟是压电晶体, 但是要在半导体芯片上集成压电晶体是不是有点难度？因为压电晶体时钟实际是机械振动时钟 必须要能独立振动才行。
当然cpu或者gpu封装的时候可以在底面或者铁壳里塞个晶体 但是好像裸露的处理器上从来没有看到过疑似压电晶体 只见过反面有电容
另外，我看低端微处理器 microsconttroller ，经常是设计成既可以外接一个压电晶体，来得到精确的时钟，也可以脱离外部压电晶体，靠内部的RC回路产生一个不大精确的时钟。
Re: 问个真学术问题 CPU的内部时钟
跟jiml说得一样（原来主板上的石英晶体是14.318MHz. 我修显示器的时候还买过若干 没想到GHz信号也是从它翻出来的）
https://electronics.stackexchange.com/q ... es-it-work
Electrical Engineering
What generates the clock signal in a fast CPU and how does it work?
Asked 8 years, 1 month ago
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Often, for integrated circuits, a quartz crystal is used to generate the clock signal. However, this only reaches speeds in MHz. What component, or what circuit, generates signals up to 5 GHz like in computer processors?
How is it possible to increase that speed when you overclock a PC (since I don't assume that a crystal speeds up when you put a higher voltage across it, or make it cooler)?
signalclockmicroprocessorcrystalclock-speed
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edited Aug 26, 2015 at 22:01
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Why would you assume that quartz crystals only reach frequencies up to a few kilohertz ? I have a 27 MHz crystals lying in my drawer. –
Bimpelrekkie
Aug 26, 2015 at 13:04
You're right @FakeMoustache, but I meant crystals of 1 gigahertz and above. –
Markinson
Aug 26, 2015 at 13:10
OK, I have seen crystal oscillators up to 150 MHz, in practice up to 50 MHz is used. Frequencies above that are made using a PLL as Wouter mentions. I work on a product where we use a PLL to convert 25 MHz in 60 GHz ! –
Bimpelrekkie
Aug 26, 2015 at 13:12
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Actually crystal oscillators can easily go up to 10's of MHz. Above that in most cases a PLL (Phase Locked Loop) is used, which is an oscillator that is not very accurate in itself, but can be tuned (its frequency can be adjusted somewhat). The frequency of this high-frequency oscillator is divided by a suitable factor (dividing a signal by a power of 2 is easy and totally accurate), and then compared to a let's say a 10 MHz oscillator. The comparison is used to adjust the high-frequency oscillator. Thus a high frequency is made with (almost) the accuracy of the lower frequency crystal oscillator.
In most cases, the circuitry to do all this is built into the processor chip. This is so it can be configured under software control, and routing such a high-frequency signal between chips is a nightmare.
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edited Feb 24, 2021 at 16:40
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answered Aug 26, 2015 at 13:01
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It was true 5 years ago (and probably still today) that most motherboards have a good old-fashioned 14.318MHz crystal, and a clock generator (PLL) chip that generates other bus frequencies like 33MHz (PCI), 48MHz (USB), and an intermediate "FSB" frequency like 100 or 200 MHz from there. The CPU then takes the FSB frequency and multiplies it up to the GHz range with another PLL on-chip, which avoids the problem of actually transporting the GHz clock any distance or getting it through the CPU pins
–
hobbs
Aug 26, 2015 at 17:33
https://electronics.stackexchange.com/q ... es-it-work
Electrical Engineering
What generates the clock signal in a fast CPU and how does it work?
Asked 8 years, 1 month ago
Modified 2 years, 7 months ago
Viewed 21k times
17
Often, for integrated circuits, a quartz crystal is used to generate the clock signal. However, this only reaches speeds in MHz. What component, or what circuit, generates signals up to 5 GHz like in computer processors?
How is it possible to increase that speed when you overclock a PC (since I don't assume that a crystal speeds up when you put a higher voltage across it, or make it cooler)?
signalclockmicroprocessorcrystalclock-speed
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edited Aug 26, 2015 at 22:01
Peter Mortensen's user avatar
Peter Mortensen
1,67633 gold badges1717 silver badges2323 bronze badges
asked Aug 26, 2015 at 12:58
Markinson's user avatar
Markinson
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Why would you assume that quartz crystals only reach frequencies up to a few kilohertz ? I have a 27 MHz crystals lying in my drawer. –
Bimpelrekkie
Aug 26, 2015 at 13:04
You're right @FakeMoustache, but I meant crystals of 1 gigahertz and above. –
Markinson
Aug 26, 2015 at 13:10
OK, I have seen crystal oscillators up to 150 MHz, in practice up to 50 MHz is used. Frequencies above that are made using a PLL as Wouter mentions. I work on a product where we use a PLL to convert 25 MHz in 60 GHz ! –
Bimpelrekkie
Aug 26, 2015 at 13:12
Add a comment
2 Answers
Sorted by:
Highest score (default)
24
Actually crystal oscillators can easily go up to 10's of MHz. Above that in most cases a PLL (Phase Locked Loop) is used, which is an oscillator that is not very accurate in itself, but can be tuned (its frequency can be adjusted somewhat). The frequency of this high-frequency oscillator is divided by a suitable factor (dividing a signal by a power of 2 is easy and totally accurate), and then compared to a let's say a 10 MHz oscillator. The comparison is used to adjust the high-frequency oscillator. Thus a high frequency is made with (almost) the accuracy of the lower frequency crystal oscillator.
In most cases, the circuitry to do all this is built into the processor chip. This is so it can be configured under software control, and routing such a high-frequency signal between chips is a nightmare.
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edited Feb 24, 2021 at 16:40
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CommunityBot
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answered Aug 26, 2015 at 13:01
Wouter van Ooijen's user avatar
Wouter van Ooijen
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It was true 5 years ago (and probably still today) that most motherboards have a good old-fashioned 14.318MHz crystal, and a clock generator (PLL) chip that generates other bus frequencies like 33MHz (PCI), 48MHz (USB), and an intermediate "FSB" frequency like 100 or 200 MHz from there. The CPU then takes the FSB frequency and multiplies it up to the GHz range with another PLL on-chip, which avoids the problem of actually transporting the GHz clock any distance or getting it through the CPU pins
– hobbs
Aug 26, 2015 at 17:33
Re: 问个真学术问题 CPU的内部时钟
现在北桥没了 内存控制器直接在CPU芯片上， CPU和内存之间以1到2G赫兹的时钟频率直接通信。CPU本身通过DMI和PCH通信。huangchong 写了： ↑2023年 10月 8日 18:52 跟jiml说得一样（原来主板上的石英晶体是14.318MHz. 我修显示器的时候还买过若干 没想到GHz信号也是从它翻出来的）
https://electronics.stackexchange.com/q ... es-it-work
Electrical Engineering
What generates the clock signal in a fast CPU and how does it work?
Asked 8 years, 1 month ago
Modified 2 years, 7 months ago
Viewed 21k times
17
Often, for integrated circuits, a quartz crystal is used to generate the clock signal. However, this only reaches speeds in MHz. What component, or what circuit, generates signals up to 5 GHz like in computer processors?
How is it possible to increase that speed when you overclock a PC (since I don't assume that a crystal speeds up when you put a higher voltage across it, or make it cooler)?
signalclockmicroprocessorcrystalclock-speed
Share
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edited Aug 26, 2015 at 22:01
Peter Mortensen's user avatar
Peter Mortensen
1,67633 gold badges1717 silver badges2323 bronze badges
asked Aug 26, 2015 at 12:58
Markinson's user avatar
Markinson
31711 gold badge44 silver badges88 bronze badges
1
Why would you assume that quartz crystals only reach frequencies up to a few kilohertz ? I have a 27 MHz crystals lying in my drawer. –
Bimpelrekkie
Aug 26, 2015 at 13:04
You're right @FakeMoustache, but I meant crystals of 1 gigahertz and above. –
Markinson
Aug 26, 2015 at 13:10
OK, I have seen crystal oscillators up to 150 MHz, in practice up to 50 MHz is used. Frequencies above that are made using a PLL as Wouter mentions. I work on a product where we use a PLL to convert 25 MHz in 60 GHz ! –
Bimpelrekkie
Aug 26, 2015 at 13:12
Add a comment
2 Answers
Sorted by:
Highest score (default)
24
Actually crystal oscillators can easily go up to 10's of MHz. Above that in most cases a PLL (Phase Locked Loop) is used, which is an oscillator that is not very accurate in itself, but can be tuned (its frequency can be adjusted somewhat). The frequency of this high-frequency oscillator is divided by a suitable factor (dividing a signal by a power of 2 is easy and totally accurate), and then compared to a let's say a 10 MHz oscillator. The comparison is used to adjust the high-frequency oscillator. Thus a high frequency is made with (almost) the accuracy of the lower frequency crystal oscillator.
In most cases, the circuitry to do all this is built into the processor chip. This is so it can be configured under software control, and routing such a high-frequency signal between chips is a nightmare.
Share
Cite
Follow
edited Feb 24, 2021 at 16:40
Community's user avatar
CommunityBot
1
answered Aug 26, 2015 at 13:01
Wouter van Ooijen's user avatar
Wouter van Ooijen
48.5k11 gold badge6363 silver badges136136 bronze badges
8
It was true 5 years ago (and probably still today) that most motherboards have a good old-fashioned 14.318MHz crystal, and a clock generator (PLL) chip that generates other bus frequencies like 33MHz (PCI), 48MHz (USB), and an intermediate "FSB" frequency like 100 or 200 MHz from there. The CPU then takes the FSB frequency and multiplies it up to the GHz range with another PLL on-chip, which avoids the problem of actually transporting the GHz clock any distance or getting it through the CPU pins
hobbs
Aug 26, 2015 at 17:33
估计时钟信号的源头是从主板通过DMI 传递给CPU的。然后CPU和内存之间的时钟应该是内置内存控制器从CPU得到的。