[SI-LIST] Re: How to improve non monotonic
- From: "Salkow, Steven" <steven.salkow@xxxxxxxx>
- To: "'Carrier, Patrick'" <Patrick_Carrier@xxxxxxxxxx>, "'Lockard, Nickolaus J.'" <Nickolaus.Lockard@xxxxxxx>, "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 18 Jan 2010 12:09:09 -0700
Hi Nick
I agree with Patrick Carrier
1. Make sure you are looking at the receiver (I have simulated this and have a
hard time getting any non-monotonic waveform at the reciever when the driver is
LVCMOS capable of 24 ma drive using stripline or microstrip at 50 ohms)
(increase the R to 50 ohms but I believe the risetime of your driver must be
very fast)
2. Make sure your IBIS model for the driver is good
Steven salkow
Lockheed
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Carrier, Patrick
Sent: Thursday, January 14, 2010 10:33 AM
To: Lockard, Nickolaus J.; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: How to improve non monotonic
Hi Nick--
Usually, termination works best. In the case you describe below, with
your series termination, it sounds like you should have nice clean
edges. Some ideas as to why you might be seeing the glitch:
If this is in a simulation:
1. Make sure you are looking at the receiver signal
2. Make sure your IBIS model waveforms for the driver look good
3. Make sure you are using an LVCMOS or similar input impedance receiver
Or if this is a lab measurement:
1. Make sure you are looking at the receiver signal
2. When measuring, make sure you are using a high bandwidth,
high-impedance probe, that is connected close to the receiver without
any large wires on the signal probe or the reference connection
3. If you are doing all that, this glitch could also be crosstalk or
ground bounce, so you may want to look into that as well
--Pat
Patrick Carrier
Technical Marketing Engineer
High Speed Design
Mentor Graphics Corporation
Patrick_Carrier@xxxxxxxxxx
ph. (512) 425-3015
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Lockard, Nickolaus J.
Sent: Thursday, January 14, 2010 12:00 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] How to improve non monotonic
Hello,
In general, how can one improve the quality of an LVCMOS clock signal
that has a non-monotonic trailing edge?
The circuit is an LVCMOS driver, 25MHz, 3.3V, with a series 33.2 ohm
resistor at the driver, 50 ohm trace, 4 inches. The problem is the
trailing edge of the clock starts to rise back up and approach the
allowable threshold before it begins to fall back to 0V. How can this
rise be dampened, or eliminated?
Thanks,
NL
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