Re: [SI-LIST] : Via Capacitances ...

Mike Jenkins ([email protected])
Mon, 12 Jul 1999 14:01:48 -0700

Messages sorted by: [ date ][ thread ][ subject ][ author ]
Next message: Robert Tsai: "Re: [SI-LIST] : Some Semiconductors are Unnecessarily Fast"
Previous message: Roy Leventhal: "[SI-LIST] : Some Semiconductors are Unnecessarily Fast"
Maybe in reply to: Douglas McKean: "[SI-LIST] : Via Capacitances ..."
Next in thread: Fred Balistreri: "Re: [SI-LIST] : Via Capacitances ..."

[email protected] wrote:
>
> I agree with Ron's email on via being nothing but a capacitive stub.
>
> One can verify that by measuring a typical via with a TDR.
> Run a length of trace with an open via in the middle and launch a TDR signal
> (~35pS) from one end. Make sure the line is terminated in its characteristic
> impedance. You will discover a negative reflection (capacitive discontinuity).
>
> The equivalent capacitance can be derived by utilizing the reflected voltage,
> risetime, incident voltage and Zo.
>
> Michael Cheong

Michael,

Using risetime to calculate capacitance from a TDR trace is
problematic since it continually degrades. For a capacitance,
C, along a transmission line of impedance Zo, the AREA of the
reflection is the time constant Zo*C/2, exactly. (This can be
shown from the LaPlace final value theorem.)

Regards,
Mike

_____________. . . . . . . . ._____________
/ \ _/
/ \ Zo*C/2 __/
/ \________/
/
____/

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Mike Jenkins               Phone: 408.433.7901            _____     
 LSI Logic Corp, ms/G715      Fax: 408.433.7461        LSI|LOGIC| (R)   
 1525 McCarthy Blvd.       mailto:[email protected]        |     |     
 Milpitas, CA  95035         http://www.lsilogic.com      |_____|    
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**** To unsubscribe from si-list: send e-mail to [email protected]. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP.  si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****

Next message: Robert Tsai: "Re: [SI-LIST] : Some Semiconductors are Unnecessarily Fast"
Previous message: Roy Leventhal: "[SI-LIST] : Some Semiconductors are Unnecessarily Fast"
Maybe in reply to: Douglas McKean: "[SI-LIST] : Via Capacitances ..."
Next in thread: Fred Balistreri: "Re: [SI-LIST] : Via Capacitances ..."