Re: [SI-LIST] : What speed scope should I consider? / "transient impedance"

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From: Mike Degerstrom (degerstrom.michael@mayo.edu)
Date: Mon Nov 15 1999 - 06:33:55 PST


Jeremy,

You mention 'intantaneous Z=V/I'. Is this or should this really be
Z(I)=dV/dI?

Mike

On Nov 12, 7:36pm, Jeremy Plunkett wrote:
> Subject: RE: [SI-LIST] : What speed scope should I consider? / "transient
>
> Arpad,
> A technique I've used is to measure the current using a differential probe
> across a resistor in series with the DUT, and using another probe measure
> the voltage on the pin relative to ground or vdd. You can then calculate
> instantaneous Z = V/I using algebraic functions in the scope. The Tektronix
> probes I used had a specified bandwidth of 1.5GHz; if you needed to you
> might be able to set up a 3 or 4-channel TDR(i.e. 20GHz class scope w/
> passive probes) in one chassis to get a measurement out to much higher
> frequencies (2 channels are required to get the diff. meas).
>
> Some difficulties of this method are:
> 1) Any measurement of transient/instantaneous impedance will be affected by
> parasitic capacitance and inductance in your measurement setup (including
> probe input capacitance).
> 2) Buffer behavior may be dependent on the load seen at the pin; if it's
> practical you may want to take measurements with several different load
> values, both resistive and capacitive.
> 3) The measurement described above includes the impedance of the IC package
> power and ground connections in the results, therefore it will also be
> affected by the number of buffers switching, supply bypassing on the board,
> etc.
>
> Hope you find this useful!
>
> Jeremy Plunkett
> Signal Integrity Engineer
> Reliance Computer Corp.
> jeremy@rccorp.com
>
>
> -----Original Message-----
> From: owner-si-list@silab.eng.sun.com
> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Muranyi, Arpad
> Sent: Friday, November 12, 1999 4:47 PM
> To: 'si-list@silab.eng.sun.com'
> Subject: RE: [SI-LIST] : What speed scope should I consider?
>
>
> I meant impedance vs. time, or non steady state but varying impedance,
> such as the impedance of a buffer turning on/off vs. time.
>
> Arpad
> ==========================================================================
>
> -----Original Message-----
> From: Ron Miller [mailto:rmiller@Brocade.COM]
> Sent: Friday, November 12, 1999 3:54 PM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : What speed scope should I consider?
>
>
> Try Tektronix 11801 or a similar sampling scope from HP with the
> TDR option.
>
> Ron Miller
>
>
> "Muranyi, Arpad" wrote:
>
>
> Does anyone know of any instrument that can measure transient impedance?
>
> Arpad Muranyi
> Intel Corporation
> ========================================================================
>
>
> Quote from previous correspondence:
>
>
> "Network analyzers measure steady state impedance, not transient impedance."
>
>
>
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> --
>
> Ronald B. Miller _\\|//_ Signal Integrity Engineer
>
> (408)487-8017 (' 0-0 ') fax(408)487-8017
>
> ==========0000-(_)0000===========
>
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>
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>
>-- End of excerpt from Jeremy Plunkett

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