Re: [SI-LIST] : Some Semiconductors are Unnecessarily Fast

Steve Weir (weirsp@a.crl.com)
Wed, 14 Jul 1999 17:04:03 -0700

I have been looking for a fabricator who supports this, but have not found
one. Does anyone know of one?

Regards,

Steve.
At 02:20 PM 7/14/99 -0500, you wrote:
>
>
>All,
>
>I'm also hearing that the microwave guys are using thick film printed
>resistors,
>as part of the etch, for termination elements - even on internal signal
layers.
>Anybody out there willing to share experiences?
>
>
>Regards,
>
>Roy
>
>
>
>
>
>
>Philip Gantt <pgantt@cisco.com> on 07/14/99 12:42:09 PM
>
>Please respond to si-list@silab.eng.sun.com
>
>Sent by: Philip Gantt <pgantt@cisco.com>
>
>
>To: si-list@silab.eng.sun.com
>cc: (Roy Leventhal/MW/US/3Com)
>Subject: Re: [SI-LIST] : Some Semiconductors are Unnecessarily Fast
>
>
>
>
>Has anyone considered that if a more resistive material (other than copper)
>were
>used for PCB laminates, the inherent resistance of the conductors would slow
>the
>edge rates and also reduce EMI? This might eliminate the need for
>external resistors as well. Just a thought...
>
>Jon Keeble wrote:
>
>> I've seen one or two interesting approaches to controlling edge speeds.
>>
>> The first was a method of controlling the edge speed:
>> The Analog Devices 21020 DSP chip has an external resistor for setting
>> edge speeds (all outputs). I've no idea how this works internally.
>>
>> The other method reduced the production spread of edge speeds:
>> It seems that the parts that run faster also have faster edges.
>> The method involved
>> - an onboard oscillator that ran at a speed determined by the speed of
>> the device
>> - internal control on the output drivers to vary the edge speed
>> - a circuit that translated the oscillator speed to more or less drive
>> on the outputs
>>
>> As a designer, it is obvious tpo me that there is a real need for
>> control over edge speeds.
>>
>> I find it really exhausting to have to add hundreds of external
>> resistors, not to mention the additional costs, numbers of parts,
>> numbers of nodes to test etc etc.
>>
>> I'd encourage the IC designers to be a bit more inventive.
>>
>> Jon Keeble.
>>
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