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Al Farouk
Joined: 13 Jan 2003
Posts: 194
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 18 May 2003 10:13 When the PCB design is considered to be high speed |
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Dear all
I'm asking for figers of merit to consider the PCB design to be high speed desin. i.e what are the limit of frequency of the signals carried by the tracks, the length of tracks, ....etc.
Regards
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mr_ghz
Joined: 01 Apr 2002
Posts: 294
Helped: 2
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| 18 May 2003 11:18 |
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Hi Al Farouk
What do you want to design: a digital or an anlog system? In which
frequency range should the system be working?
Bye
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Al Farouk
Joined: 13 Jan 2003
Posts: 194
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| 18 May 2003 11:52 |
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| It is digital design and the maximum frequency about 50 Mhz but I have about 6 layers.
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mr_ghz
Joined: 01 Apr 2002
Posts: 294
Helped: 2
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| 18 May 2003 12:18 |
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Hi Al Farouk,
generally you have to take attention to three things:
- The impedance of the trace is to match the impedance of your sender.
The impedance is given by the width of the trace, the thickness of your
PCB and the material (er) of your PCB. You have to take this in account
for analog signals with a frequency over 100MHz and for digital signals
over 100MHz. So this point is not as interresting for your design
- The impedance of the receiver should be the same as the impedance of
your sender, or you will get reflections. In digital designs this can cause
to problems, when the length of a trace is more than 1/10 of the wave-
length of your signal. On FR-4 the wavelength for 50MHz is about
3meters. So if you keep your traces shorter than 30cm, everything is
OK. If this is not possible you have to work with resistors that will
terminate your lines.
- The line-length of a bus system should match more or less. The phase-
difference on two bus-lines should be no more than about 10°. So the
length of these lines should match to about 1/36 of the wavelength,
this will give about 8cm max difference. This should also be a reachable
value.
It is to say that a design for 50MHz can be made without big problems if
you have proper VCC and GND (planes!).
These values I gave above are estimations!
Bye
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Al Farouk
Joined: 13 Jan 2003
Posts: 194
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| 18 May 2003 12:34 |
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Dear mr_ghz
thanks for your valuable information. I want to discuss with you two points
1- Did you get the wave length equal to 3 meter for FR4 and 50Mhz by considering that the signal travel with have the speed of light on PCB board?
2- I read that the rise of the digital signal dominat the PCB design more that the frequency of it in case it had sharp edges. as sharp edges cause high frequency components if it is analysed by fourier. so I think the rule of that 1/10 wavelengh can be mre suitably applied for the rise time of the signal rather that the ignal frequency in case of sharp edges, so the 50Mhz design can be treated as high speed design. what is your main?
Regards
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mr_ghz
Joined: 01 Apr 2002
Posts: 294
Helped: 2
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| 18 May 2003 16:31 |
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Hi Al Farouk,
A signal propagates with the speed of light in a dielectricum with er=1.
When this value is increased, the speed lowers. FR-4 has an er of about
4, so the speed will be about half. The wavelength can be calculated:
lambda=c/(f*sqrt(er)). This will result in the given 3 meters. (These
values are true when you have a proper ground plane).
Fact is that a digital signal has not only the frequency itself (e.g. 50MHz),
it also has all overtones (100MHz, 150MHz, ...). This will give the sharp
edges. This frequencies do not carry (direct) information. This frequencies
are already taken in account in the 1/10 of wavelength.
The bigger problem of these higher frequencies is the radiated power. If
you have to pass an EMC test, this can be critical. Much CPU's can lower
the sharpness of their signals, this can help. Another possibility is to take
a metal housing...
Bye
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juggernaut7
Joined: 10 May 2001
Posts: 31
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| 29 May 2003 16:51 |
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| You may be selling yourself short by limiting your discussions to 50MHz. The clock frequency may be low, but it isn't the clock freq that causes a design to be considered high speed, it is the rise time of the device. A fast device (which pretty much all new builds are) will create a signal transition that propagates down the line much faster than 50MHz. You should evaluate your design based on the parts, not the clock frequency.
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binu G
Joined: 09 Jan 2003
Posts: 729
Helped: 9
Location: Bangalore
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| 31 May 2003 1:24 help |
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| where i can get more information about the high speed design?
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wilson
Joined: 24 Jul 2002
Posts: 55
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| 31 May 2003 7:06 High Speed Design |
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Hello Binu
Here is a file which will give you a brief intro about High Speed Board Design.
Other Then this you can visit
http://www.signalintegrity.com/
a nice site to look at...
regards
Wilson
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popoyboys
Joined: 20 Feb 2007
Posts: 99
Helped: 1
Location: from the deepest roots of KAMOTE land
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| 20 Feb 2007 9:01 When the PCB design is considered to be high speed |
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| does anyone here have ebook entitled SIGNAL INTEGRITY & PRINTED CIRCUIT BOARD DESIGN by Douglas Brooks?
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tarakesava
Joined: 28 Jan 2007
Posts: 15
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| 21 Feb 2007 9:05 Re: When the PCB design is considered to be high speed |
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when ever trace behaves as a transmission line in pcb,by the time we consider as high spped design.
1)whenever trace exceeds criticl length,by the time we consider trace behaves as a transimission line.
2)when rise time of signal is less than twice of the propagation delay of the signal to travel trace ,then we conisider trace exceed the critical length.
pls inform if any thing is wrong.
thx u
Added after 18 minutes:
Signal_Integrity_Issues_And_Printed_Circuit_Board_Design.rar by dougals brooks
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venkat_kvr
Joined: 24 Jan 2007
Posts: 264
Helped: 15
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| 28 Feb 2007 5:16 Re: When the PCB design is considered to be high speed |
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| if the length of the trace is grater than the rise time length,then u can consider ur board as highspeed
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hidelove
Joined: 13 Feb 2007
Posts: 3
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| 16 Mar 2007 16:45 When the PCB design is considered to be high speed |
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| I've questions for it , Does the trace length are really relate for EMI , becuase I seem many trace has equal the 1/4 lumda,but I can't see anything happening ,please explain why ~? Thanks !!
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AlexTien
Joined: 20 Sep 2006
Posts: 2
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| 17 Mar 2008 5:51 Re: When the PCB design is considered to be high speed |
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I think this book is great to read.
Signal Integrity - Simplified (Prentice Hall Modern Semiconductor Design Series' Sub Series: PH Signal Integrity Library) (Hardcover)
by Eric Bogatin (Author)
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panda14
Joined: 14 Jun 2007
Posts: 7
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| 24 Mar 2008 20:45 When the PCB design is considered to be high speed |
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| it depends on your rise time also, normally exceed 5% or 10% of lamba we can see the TL effects
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Thomson
Joined: 15 Oct 2004
Posts: 182
Helped: 3
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| 03 Apr 2008 4:21 Re: When the PCB design is considered to be high speed |
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| AlexTien wrote: |
I think this book is great to read.
Signal Integrity - Simplified (Prentice Hall Modern Semiconductor Design Series' Sub Series: PH Signal Integrity Library) (Hardcover)
by Eric Bogatin (Author) |
Five Star book on amazon and tells your much about signal integrity!
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Fom
Joined: 10 Mar 2004
Posts: 720
Helped: 52
Location: Taiwan
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| 03 Apr 2008 8:11 When the PCB design is considered to be high speed |
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From "Electromagnetics explained" book:
5/5 rule
If any signal has a frequency greater than 5MHz or has edges faster than 5 nsec you should use ground plane.
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prasad5551
Joined: 16 Apr 2008
Posts: 10
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| 25 Apr 2008 9:30 When the PCB design is considered to be high speed |
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hi
all concepts are given in the EMC and the printed circuit board by mark.I.montrose from ieee press,u can download from ebookee.com
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Timgonghe
Joined: 26 Apr 2008
Posts: 1
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| 26 Apr 2008 10:09 When the PCB design is considered to be high speed |
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| If 1/3 or more of your digital circuit speed excced 40~50MHz, we generally call it high speed.
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ar_m_in
Joined: 20 Jun 2006
Posts: 28
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| 07 May 2008 17:10 When the PCB design is considered to be high speed |
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Nice info from diff people
thanks
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panda14
Joined: 14 Jun 2007
Posts: 7
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| 11 May 2008 11:45 When the PCB design is considered to be high speed |
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| thanks for all sharing on high speed design, learned a lot from here.
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electron_boy
Joined: 14 Nov 2004
Posts: 197
Helped: 18
Location: Chennai, India
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