[SI-LIST] Re: Waveform edge ringing
- From: Eddy <eddyvk@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 6 Dec 2010 22:35:53 -0800 (PST)
This looks like the waveform on an input somewhere halfway the daisy chain.
When you match a CMOS driver to a trace with a series resistor and then leave
the trace open at the very end, this is only good when you have just one input
at the very end of that trace. Halfway the trace you will see reflections like
the "ringing" as you call it halfway low and high levels. The only way to get
rid of the reflections is to properly terminate the end of the trace but that
will be difficult to do with CMOS levels.
Perhaps you can filter the signal where you are tapping off the trace somewhere
halfway. A ferrite bead in series with the signal might "choke" the high
frequency ring enough so it becomes monotonic rising at the target input.
Eddy van Keulen
Sr. FAE Mgr., PhaseLink Corp.
KF6PLO
--- On Tue, 11/23/10, Nijagunamurthy, Hithesh (GE Intelligent Platforms)
<hithesh@xxxxxx> wrote:
From: Nijagunamurthy, Hithesh (GE Intelligent Platforms) <hithesh@xxxxxx>
Subject: [SI-LIST] Waveform edge ringing
To: si-list@xxxxxxxxxxxxx
Date: Tuesday, November 23, 2010, 2:53 AM
I am doing signal integrity simulation for PCI Address/Data bus signals
going from an FPGA to a Power PC.
The signals are daisy chained from the FPGA to 6 Power PCs. The daisy
chain routing is 55 ohm impedance controlled.
The waveform edge has some ringing at VIH on the rising edge and VIL at
the falling edge. The ringing is only for one cycle(see pic).
Can this be counted as a valid waveform.
Let's say this is input to a clock buffer.
The part where I am confused is(on the rising edge) the waveform goes
above VIH, so now the output of the receiver IC should be High. Now if
the edge goes 200mV below VIH after say 1ns, and comes back to Vcc, will
the output of the receiver change?
There is similar behavior at VIL.
Now, let's say this is Addr or data line. Would the setup time would be
violated?
Image - http://www.imgplace.com/viewimg217/6307/69wave.jpg
Thanks.
-Hithesh
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