[SI-LIST] Re: over & under shoots

To distinguish between problems in the opamp driver and the line-termination
load
try disconnecting the output from the line and locally terminating it.
Remember the output impedance of an opamp with feedback is very low,
thus reflections will not be obsorbed.

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Regards,    __________   James G Roberts
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 Jim      __  / /___/ /  jgroberts@xxxxxxxxxx
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Tom Dagostino wrote:

> You also need to check your measurement system.  If you have a long ground
> wire on your scope probe you will get overshoot displayed on the scope that
> is not in the circuit you designed.
>
> Tom Dagostino
> Teraspeed Consulting Group LLC     Teraspeed Consulting Group LLC
> 2926 SE Yamhill St.                Device Modeling Division
> Portland, OR 97214                 13610 SW Harness Lane
>                                    Beaverton, OR 97008
> http://www.teraspeed.com           503-430-1065
> tom@xxxxxxxxxxxxx
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of James_R_Jones@xxxxxxxx
> Sent: Thursday, January 23, 2003 6:37 AM
> To: sajith_emsys@xxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: over & under shoots
>
> I might check out the following:
>
> 1.  Measure the power supply at the amplifier power pin relative to the
> nearest ground pin on the amp.  See if there is noise synchronous to the
> switching.  If so, you may need to add decoupling caps to quiet the supply.
>
> 2.  Redraw the circuit including parasitics such as input/output
> resistance/capacitance included on the datasheet for the amp.  You may have
> created a second order system at either the input or output of the amp.
> Second order systems have a tendency to ring.  You could even do a spice
> simulation of this circuit and see if you can reproduce the ringing and
> maybe how to reduce the ringing.
>
> Hope this helps,
> James R. Jones
> Dell
>
> -----Original Message-----
> From: Sajith E K [mailto:sajith_emsys@xxxxxxxxxxxxxxx]
> Sent: Thursday, January 23, 2003 6:56 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] over & under shoots
>
> hi all,
>
> I have  a very basic problem on my board
> A discrete analog amplifier which is suppose to amplify a 2KHz square wave
> gives undershoots at the output.
> Could any one please explain the possible reasons for over and undershoots
> and measures to aviod it.
> Since i am novice in the field i seek ur earnest co operation in solving the
> issue.
>
> thanks in advance
>
> SAJITH
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