[SI-LIST] SV: Impedance calcuation

Well the interesting question is what kind of rise/fall-times is the =
driver using,
in your case device 1. This rise/fall-time will show approx. how far =
from the driver
the driver will see your circuits lumped effects after that distance =
the driver will
see characteristic impedance of the line (lines if that would include =
any forks).

(of course you also need to know the speed of the signal in the actual =
layer on your
board. your stackup will define that)

If you want to optimize the topology you better simulate it.

Regards /Anders Ekholm

-----Ursprungligt meddelande-----
Fr=E5n: Joe Young [mailto:joeyoung10@xxxxxxxxx]
Skickat: den 15 april 2002 23:53
Till: si-list@xxxxxxxxxxxxx
=C4mne: [SI-LIST] Impedance calcuation



Hi Experts,
        I have a very basic (silly?) question in my mind. I need to =
calculate the total load or impedance faced by the Driver.I know the =
input capacitance of the receivers. And also i know/decide the trace =
length information.
         Device1 --- 8.8 nH , 1.0PF
         Device2 --- 6 nH, 2 pF
         Device3 --- 8 nH, 7 pF
         Device4 -- 3.3nH 0.7 pF
         Device5 -- 3.3nH 0.7 pF and assume device 2 is 1 inch from =
device 1 and device 3 is 2 inch from Device 1(1 inch from Device 2) and =
Device 4 and 5 are 4 inch from device 1 (2 inch from device 3)
      =20
     Device 1 drives Device2 to Device 5.
            I have to come up with a best topology. Device 2 operates =
at 83 Mhz and Device3 to 5 operates at 33 Mhz.
     Now i want to know the impedance seen by the Device 1 when it is =
driving the loads.
    Ofcourse, i can refer the books. But i would like to know is there =
any easier formula for come to quickest conclusion to decide th =
topology? Any thumb rule?.Reference to any formula?.
    Am i missing any parameter that has to be included?                 =
     =20
    This question may be a very basic and can be found in books but i =
would like to hear from the Experts to know  how they would decide.     =
        =20
      =20
Expecting the inputs from the experts to add up my experience.

If anybody could give me a detailed paperwork, really it would be =
helpful for me to do further experiments.

rgds,
Joe

        =20





















       =20




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