[SI-LIST] Re: How does the loading affects the rise time of a PAD?
- From: "Peterson, James F (FL51)" <james.f.peterson@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 21 Aug 2001 12:02:22 -0400
The 50 ohm 15 inch long transmission line is a thing of beauty. It will not
degrade your rise time. It will appear like a resistor (50ohms) to the
buffer, therefore you do not need to "lump" the capacitance (see the bottom
of page 143 of the "black magic" book by Johnson and Graham....).
best regards,
Jim
-----Original Message-----
From: C.Y. Cheng [mailto:cyc@xxxxxxxxxxxxx]
Sent: Monday, August 20, 2001 12:05 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] How does the loading affects the rise time of a PAD?
Hi folks,
I have got a basic problem to choose a PAD for GMII interface.
The system requires a PAD which could drive a 5 pF loading in
1ns rise time.
If I can choose a PAD which could drive a 3-inches long, 50 ohms
transmission line and meet spec. .
What if I use the same pad to drive a 15-inches long, 50 ohms
transmission line? The lump capacitance may increase to be 5 times of
previous case. Will it " slow down " the rise time of the PAD ?
Thanks,
C.Y. Cheng
ASIC designer
ADMtek Taiwan
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