Re: [SI-LIST] : IC input impedance

Dima Smolyansky (dima@easystreet.com)
Tue, 13 Oct 1998 11:11:08 -0700

Agreed, good point - capacitance will probably be the main term in your CMOS
driver characteristics.

I also want to comment on Glenn Monroe's knee frequency comment. I think the
knee frequency will give an easimate for the reflection coefficient for
high-order harmonics, which are not the most important in esimating how much of
your digital signal is reflected. If your 8th order harmonic is reflected
almost completely, you could not care less, even if it is below the knee
frequency. At the same time, the relfection coefficient at the 1st harmonic
will give you a pretty good idea of how much amplitude you will loose in your
digital signal.

Thanks,

-Dima

=========================
Dima Smolyansky
TDA Systems, Inc.
7465 SW Elmwood St.
Portland OR 97223
503-977-3629
503-245-5684 (FAX)
dima@tdasystems.com
http://www.tdasystems.com

Johnson, David wrote:

> Dima:
>
> Are you talking about series R and shunt C? Shouldn't the model be shunt R
> and shunt C, with an equation more like Z = 1 / (1/R + jwC) = R / (1+jwRC)?
> I always thought CMOS inputs acted pretty much like pure capacitors, on the
> order of 5 pF or so.
>
> ---- david.johnson@intel.com
>
> -----Original Message-----
> From: Dima Smolyansky [mailto:dima@tdasystems.com]
> Sent: Tuesday, October 13, 1998 8:18 AM
> To: 'Shimon_Turgeman@amat.com'
> Cc: si-list@silab.Eng.Sun.COM
> Subject: RE: [SI-LIST] : IC input impedance
>
> I would guess, the main harmonic of the clock, as it is at this frequency
> that you will get the most amplitude loss.
>
> BTW, if you estimate the R in the equation I proposed, it may swarm the
> value of 1/jwc in the overall impedance and make it negligible.
>
> Anybody, any other good ideas?
>
> Thanks,
>
> -Dima
> ============================
> Dima Smolyansky
> Marketing and System Development
> TDA Systems, Inc.
> 7465 SW Elmwood St.
> Portland, OR 97223
> (503) 977-3629
> (503) 245-5684
> dima@tdasystems.com
> http://www.tdasystems.com
>
> -----Original Message-----
> From: Shimon_Turgeman@amat.com [SMTP:Shimon_Turgeman@amat.com]
> Sent: Tuesday, October 13, 1998 6:52 AM
> To: Dima Smolyansky
> Subject: RE: [SI-LIST] : IC input impedance
>
> what is the relevant frequency w of j*w*c?
>
> Dima Smolyansky <dima@tdasystems.com> on 10/13/98 05:44:33 PM
>
> To: "'Shimon_Turgeman@amat.com'" <Shimon_Turgeman@hermes.mis.amat.com>,
> "si-list@silab.Eng.Sun.COM" <si-list@silab.Eng.Sun.COM>
> cc: (bcc: Shimon Turgeman/AME/APPLIED MATERIALS)
> Subject: RE: [SI-LIST] : IC input impedance
>
> I suppose, R+1/j*w*c?
>
> Thanks,
>
> -Dima
> ============================
> Dima Smolyansky
> TDA Systems, Inc.
> 7465 SW Elmwood St.
> Portland, OR 97223
> (503) 977-3629
> (503) 245-5684
> dima@tdasystems.com
> http://www.tdasystems.com
>
> -----Original Message-----
> From: Shimon_Turgeman@amat.com [SMTP:Shimon_Turgeman@amat.com]
> Sent: Tuesday, October 13, 1998 12:55 AM
> To: si-list@silab.Eng.Sun.COM
> Subject: [SI-LIST] : IC input impedance
>
> what is the input impedance of CMOS devices (for calculating the reflection
> coff.)as a function of input capacitance ? how I calculate this impedance ?
> what is the formula ?
>
> Best Regards
> Shimon Turgeman
> Applied Materials
>
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