[SI-LIST] Re: Doubt about RC constant Low Pass Filter
- From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 5 Aug 2013 16:04:29 +0000
All,
While it is true that circuit elements provided by the GUI toolbar
in HyperLynx include mounting parasitics, you can also build circuits
in HyperLynx with "pure" SPICE circuit elements as in any other SPICE
simulator. You just need to be familiar enough with HyperLynx to know
how to do it. While HyperLynx is an easy to use tool, it is also very
sophisticated with zillions of features and capabilities. If you need
help with HyperLynx, please do not hesitate to ask for help from your
local Mentor technical support team. Public discussion forums like this
one are not the place to get such help.
Fan,
To be honest, I really don't understand the details of your original
problem description. I suspect that there may be fundamental errors in
the calculations (for example omitting the PCB trace impedance, or the
buffer impedance, or the buffer's pad capacitance, etc...). Please
describe your circuit and calculations with a little more detail so
we can see better what you are trying to do.
Thanks,
Arpad
=========================================================================
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Grasso, Charles
Sent: Monday, August 05, 2013 10:15 AM
To: cnmuggle@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Doubt about RC constant Low Pass Filter
One thing to keep an eye on is the parasitics in the models.
Hyperlynx does not provide *pure* models for C and L - by that I mean that the
models also include parastics for mounting inductance
and stray capacitance. So, for example, you may have a different parasitic
mounting inductance (by accident) selected between models.
Its unlikely that this is your problem - just one thing to check.
I have found that Spice is the best tool for "simple" models! Try your
calculations in Spice and confirm your calculations.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Fan Gaofeng
Sent: Monday, August 05, 2013 3:09 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Doubt about RC constant Low Pass Filter
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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