What is common mode, frequency dependence dielectric loss in PCB?

[chuan556]

i have several questions to ask and hopefully anyone here can help me:

1)what is common mode?
2)when we simulate a pcb's trace with 90 degree bend,we must add a segment of capacitance to the simulation software.Why?
3)i wish to know more about frequency dependance dielectric loss that explained by johnk 1988.

thanks.

 

[House_Cat]

Re: req:question on pcb

1. Common mode is a signal common to both + and - input terminals of a device. In a differential amplifier, it is the unwanted part of the signal measured between each input connection and the reference plane that is added to each original signal.

2. When a trace is made with a 90deg bend, the corner is very slightly wider than either trace entering the corner. To account for that small amount of extra copper on the outside vertex of the corner, a small parasitic capacitance can be added to the simulation. In all but extremely high frequency RF, or exceptionally fast edge rates, the additional capacitance of the corner is negligible compared with the overall trace capacitance.

3.Look here for a pretty good explanation of dielectric loss with frequency: http://www.sigcon.com/Pubs/news/4_5.htm
Use Google and search - you will find references to many papers on the subject.

 

[chuan556]

req:question on pcb

why the link cannot use?
by the way, what is package stub, distributed model?
thanks

 

[House_Cat]

Re: req:question on pcb

why the link cannot use?

Sorry about that - there were extra characters at the end of the link that didn't belong - it works now.

As for your other questions - the list of questions you have posted are begining to sound suspiciously like homework for a student. I learned what I know by doing my OWN homework. You should do the same.

I typed "package stub" into Google, and the definition was the second item on the resulting list. Both of the definitions you seek should be equally easy to find.

 

[chuan556]

req:question on pcb

actually this is not the homework but rather a term that
used in a book(high speed digital system-wiley,hall stephen H).
i am working on the stiching cap,and this is literature part where i should learn the basics first since i am not the electrical background(i am physics engineering student).
i try to search on yahoo already before i post this.
thanks anyway.

 

[House_Cat]

Re: req:question on pcb

The package stub consists of all the pieces that connect an integrated circuit die to the outside world through the IC package - the bonding pad, the bonding wire, the internal pin connection, and the external IC pin. It is taken into account when you do a distributed model of the IC. See the following for a definition of distributed model.

There are two ways you can model an electronic circuit - lumped and distributed.

The lumped model assumes that the device you are modeling is a black box with two terminals, and there is one inductance, resistance, and capacitance across the terminals that represent what is seen by the connected circuitry outside the black box - for the purpose of modeling, you don't care what is inside the box, only how it looks to the connected circuitry.

The distributed model is more detailed and looks beyond the connected terminals to describe the behavior of the black box itself. An example would be a section of transmission line - you can describe it as one specific impedance as you look into the two terminals of the transmission line (lumped model), or you can describe it as a series of connected series inductors, series resistors, parallel resistors and parallel capacitors. You then analyze what happens as a wavefront moves down the line through the distributed matrix of those equivalent component parts. Distributed modeling can also be considered piecewise modeling - representation of each small segment by an equivalent network of discrete component parts.

 

[chuan556]

req:question on pcb

thanks, i already figure it out and you are really help me a lot,now i can continue my study into stiching cap,thanks