[SI-LIST] Doubt about RC constant Low Pass Filter
- From: Fan Gaofeng <cnmuggle@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 5 Aug 2013 17:09:08 +0800
Hi, Si-List friends,
This is my first post. I do a very simple simulation in Hyperlynx about RC
low pass filter to estimate scope bandwidth influence toward IO buffer
output rise time.
The time constant I choose is 22.5 ps = 1 K ohm * 23 fF = 50 * 450 fF
and use the Kintex-7 IBIS file buffer SSTL15_F_HP. Actually, I expect that
the rise time I got from C1 and C2 is same. But the result surprises me.
The RC circuit of 50 ohm * 450 fF gives me a rise time of *169ps* while the
1 Kohm * 23 fF gives me a rise time of *1.077ns*. Can anyone told me why
does that happen?
Regard
* *
*Fan* Gaofeng
http://About.me/Fan.Gaofeng
Fan Gaofeng
PHONE:+65 9130 5759
about.me/Fan.Gaofeng/
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