[SI-LIST] Re: Testing question about oscilloscope
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: <zkun.zhang@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 15 Jan 2013 08:55:10 -0800
Zhang
You gave very little data so we can only speculate about your problem.
I'll assume you are looking at a fast rising or falling edge and are seeing
overshoot that is well above the power supply rail or well below the "ground
reference". I'll also assume you do not have an adequate ground point for
the scope probes ground lead. This is a very typical setup that can cause
large overshoot and ringing on a waveform that should be confined to the
region between ground and the power rail. For high speed probing you need a
ground close to the test point and a very short ground path from the probe
tip to the DUT. The loop that forms from test point to probe to ground lead
to circuit ground to test point forms an inductor. The larger the loop the
more inductance and the larger the overshoot will be.
The other typical issue that can cause overshoot and ringing comes from
non-terminated transmission lines. From your basic Lines and Networks
theory and non-terminate or poorly terminated transmission line will have
reflections which can be seen on a scope.
Tom Dagostino
Teraspeed Labs
9999 SW Wilshire St.
Suite 102
Portland, OR 97225
USA
971-279-5325 Office
971-279-5326 FAX
503-430-1065 Cell
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
16 Stormy Brook Road
Falmouth, ME 04105
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Zhangkun (Zkun)
Sent: Tuesday, January 15, 2013 1:27 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Testing question about oscilloscope
Hi all
We test signal of 5V. There is a oscillating, which is about 80ns, 4V-8V.
Is it because of grounding?
Best Regards
Zhangkun
2013/1/15
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