How does computers work at Ghz range ?

[neptune]

Hello folks,
From what i see CPU are working at 3 Ghz speed.
That is L-band and S-band of microwave frequency spectrum. these high freq. can not be transffered through copper or any metal , metal has very high impedance at that freq.

So how does data transffer takes place ?

 

[JimB]

these high freq. can not be transffered through copper or any metal , metal has very high impedance at that freq.

Wrong!
What makes you think that?

So how does data transffer takes place ?

All connections are as short as possible and designed as transmission lines terminated in their characterictic impedance.

JimB

 

[neptune]

well because they use metal made waveguide to transffer signal at microwave frequency.
microwave frequency bounces back and forth in waveguide.

so you are saying that length of wire is made to match the wavelength of microwave ?

 

[ronsimpson]

well because they use metal made waveguide to transffer signal at microwave frequency.
microwave frequency bounces back and forth in waveguide. so you are saying that length of wire is made to match the wavelength of microwave ?

A wave guide, transmission line, bounces back if it is not driver correctly or is not terminated correctly.
A PCB trace, or pair of traces, used for high speed is built for 100 or 50 ohms impedance. It is driven by a IC with the matching 100 ohms output impedance and the trace is terminated with a matching 100 ohms.

 

[ronsimpson]

A different answer:
Your computer is working at 3 Ghz but it can only run small pieces of a program at that speed. The CPU and the first cash memory are together in the same piece of silicon. The CPU is using RAM that is only 0.5cm away. It does run at 3 Ghz. There is a second cash memory that is 100x larger that is 2cm away and takes more time to get to that memory so maybe the speed is only 1 Ghz. There are memory sticks 8cm running at 500mhz. Some programs (and data) are so large that they are on the hard drive's RAM and run at 10mhz or even on the hard drives platters and take (forever) to get at. There is a very complicated process of determining what data and instructions are used often and what is rarely used. Data used over and over, like a loop in software, will get pushed into memory close to the CPU. Great pieces of most programs never get used and reside far away form the CPU. So...your CPU can run at 3 Ghz and often does but part of the time it is working much slower depending on what memory it is using at that moment in time.

 

[Nigel Goodwin]

well because they use metal made waveguide to transffer signal at microwave frequency.
microwave frequency bounces back and forth in waveguide.

That's RF energy, NOT electricity - completely different things.

 

[nsaspook]

That's RF energy, NOT electricity - completely different things.

RF energy is just electricity ( electromagnetic force ) moving in free space.

Most people, including most electrical engineers, think of electricity as electrons flowing in a wire, much like water flowing in a hose. The idea of electrical energy moving through free space in a wave is a completely foreign concept. Yet, electromagnetic radiation is exactly that, electrical energy moving through space as a wave, and electrical energy in a wire is a special case in which the energy is guided by a wire. Some of the energy is internal to the wire, and some of the energy is external to the wire. When we plug an appliance into the receptacle, the power delivered to the appliance does not actually "go through the cord", but is electromagnetic energy being "guided" by the electron activity in the power cord. The electromagnetic energy delivered to the load is external to the wire. The electron activity oscillating back and forth in the wire is a result of the external electromagnetic energy and in turn serves as a way of telling the electromagnetic wave to follow the wire. The electron movement in the wire is proportional to the strength of the wave being guided. Don't be disturbed if you have difficulty grasping this concept. Even engineering students have difficulty understanding it.

https://www.osha.gov/SLTC/radiofrequencyradiation/electromagnetic_fieldmemo/electromagnetic.html

 

[Nigel Goodwin]

RF energy is just electricity ( electromagnetic force ) moving in free space.

But is completely different - and has entirely different characteristics.

 

[JimB]

Inside a waveguide, the RF energy is in the form of an electromagnetic wave, just the same as if it were in free space, except that it is constrained by the waveguide, which IS conductive.

If you look at a waveguide to coax transition, you will see that inside the waveguide is a small antenna which you could use to propagate the RF enegy into free space if you take a hacksaw and cut away the waveguide.

Inside the the coax, the RF enegy is just electrons moving about a bit. The same as DC or the 50/60hz mains supply.

JimB

 

[neptune]

what is the formula to calculate length of wire and wavelength for antenna ?
i have heard λ >> Length of wire then transit time doesnt matter

A wave guide, transmission line, bounces back if it is not driver correctly or is not terminated correctly.
A PCB trace, or pair of traces, used for high speed is built for 100 or 50 ohms impedance. It is driven by a IC with the matching 100 ohms output impedance and the trace is terminated with a matching 100 ohms.

i think this explains everything , matching of impedance with the help STUB

 

[nsaspook]

But is completely different - and has entirely different characteristics.

Not really, if you use EM field theory instead of the (near-field approximation) circuit theory they are exactly the same. The only difference is the scale. If we were to scale up a massive 60hz device to the same atomic scale as a 3ghz computer the waveguide effects and reflections would be the same. We deal with the near-field characteristics of em fields in circuit theory and normally treat current flow in wire as confined to the wire as it's usually just as accurate to do so until the dimensions shrink to a good fraction of the wavelength of flowing energy.

 

[nsaspook]

Inside a waveguide, the RF energy is in the form of an electromagnetic wave, just the same as if it were in free space, except that it is constrained by the waveguide, which IS conductive.

If you look at a waveguide to coax transition, you will see that inside the waveguide is a small antenna which you could use to propagate the RF enegy into free space if you take a hacksaw and cut away the waveguide.

Inside the the coax, the RF enegy is just electrons moving about a bit. The same as DC or the 50/60hz mains supply.

JimB

RF energy inside the coax is not electrons. Just think about it for a second, electrons have mass and can't travel at the speed of light (or even get close unless accelerated by a large electric field in almost pure vacuum). The energy carrier for electrical energy are photons. Inside the coax the confined em field travels in the dielectric instead of free space. As the photons interact with the denser matter the propagation speed slows (not the actual speed of photons) as they are regenerated by the electrons. This is why a foam dielectric (more open space between cells of denser matter) has a faster propagation factor.

If the RF energy was in the electrons, the dielectric wouldn't matter for propagation speed because it's a insulator with no free electrons for current flow but it does because the energy (RF/DC/ELECTRICITY) is not in the wire electrons.

 

[neptune]

The energy carrier for electrical energy are photons.

what RF wave is photon wave ? i would have to ask my proffesor ...

 

[JimB]

RF energy inside the coax is not electrons. Just think about it for a second, electrons have mass and can't travel at the speed of light (or even get close unless accelerated by a large electric field in almost pure vacuum). The energy carrier for electrical energy are photons. Inside the coax the confined em fields travels in the dielectric instead of free space. As the photons interact with the denser matter the propagation speed slows (not the actual speed of photons) as they are regenerated by the electrons. This is why a foam dielectric (more open space between cells of denser matter) has a faster propagation factor.

If the RF energy was in the electrons, the dielectric wouldn't matter for propagation speed because it's a insulator with no free electrons for current flow but it does because the energy (RF/DC/ELECTRICITY) is not in the wire electrons.

I am humbled by your vastly superior knowledge of this subject.

JimB

 

[nsaspook]

what RF wave is photon wave ? i would have to ask my proffesor ...

**broken link removed**
**broken link removed**

 

[nsaspook]

I am humbled by your vastly superior knowledge of this subject.

JimB

My example shows the limits of just using electrons to describe electrical energy flow. The electron charge changes and movements in a wire or a semiconductor junction is critical to the controlled flow of electrical energy in most electronics but it's only part of the story of why it functions.
A 'Bucket Brigade' of slightly moving electrons (men with buckets/matter) and fast moving photons (water/energy) is a crude analogy.

A basic understanding of QED makes it much easier to really understand electricity.

 

[nsaspook]

A little quiz that explains propagation speed.
https://www.electro-tech-online.com/custompdfs/2012/01/propagationtime.pdf

 

[davenn]

A little quiz that explains propagation speed.
https://www.electro-tech-online.com/custompdfs/2012/01/propagationtime.pdf

That was a nice explanation. I knew the answer was c but could never really have explained it properly

Am well familiar with the effects of dielectric materials on EM propagation, now I have an understandable explanation

A good reference page for sure
Thanks
Dave

 

[davenn]

RF energy inside the coax is not electrons. Just think about it for a second, electrons have mass and can't travel at the speed of light (or even get close unless accelerated by a large electric field in almost pure vacuum). The energy carrier for electrical energy are photons. Inside the coax the confined em field travels in the dielectric instead of free space. As the photons interact with the denser matter the propagation speed slows (not the actual speed of photons) as they are regenerated by the electrons. This is why a foam dielectric (more open space between cells of denser matter) has a faster propagation factor.

If the RF energy was in the electrons, the dielectric wouldn't matter for propagation speed because it's a insulator with no free electrons for current flow but it does because the energy (RF/DC/ELECTRICITY) is not in the wire electrons.

OK this does touch on things I have read elsewhere.
I do understand the EM wave leaving an antenna is photons (in fact ALL EM waves are photons.... right up through light to xrays etc, they're just higher energy ones.
I can see and understand what you are saying that the EM wave surrounding the coax's centre conductor is also photons... no problem there.
But what about the actual RF current flowing in the skin of the wire ? thats still the flow of electrons ?

if not ... where's the changeover between electron flow and EM wave propagation along a wire ?

Dave

 

[nsaspook]

The electron flow that we call current is a response to electrical energy.
Energy is the key, electrons are just a mechanism of travel for energy.
What is current? Is it energy flow?
Lets see what charge is all about. https://en.wikipedia.org/wiki/Coulomb
Lots of good things, but nothing about energy.

What is energy? https://en.wikipedia.org/wiki/Joules

The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one '"coulomb volt" (C·V).

What is electrical potential? https://en.wikipedia.org/wiki/Electric_potential

Objects may possess a property known as an electric charge. An electric field exerts a force on charged objects, accelerating them in the direction of the force, in either the same or the opposite direction of the electric field. If the charged object has a positive charge, the force and acceleration will be in the direction of the field. This force has the same direction as the electric field vector, and its magnitude is given by the size of the charge multiplied with the magnitude of the electric field.

The RF frequency current/charge that is in any section of wire is caused by flow of RF energy fields around that wire. There is no changeover, electrical energy is always moved in fields, sometimes those fields are time-invariant (DC/STATIC) or change with time (AC/RF/LIGHT/ETC...)