Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site hcr.UUCP
Path: utzoo!hcr!anton
From: anton@hcr.UUCP (Anton Aylward)
Newsgroups: net.arch
Subject: Re: Cray vs ICs, continued
Message-ID: <434@hcr.UUCP>
Date: Wed, 15-Jun-83 09:38:25 EDT
Article-I.D.: hcr.434
Posted: Wed Jun 15 09:38:25 1983
Date-Received: Wed, 15-Jun-83 09:46:34 EDT
References: <3018@utzoo.UUCP>
Organization: Human Computing Resources, Toronto
Lines: 44

Henry (utzoo!henry) although quoting, is perfecly correct.

The "whadya mean termination its only 3 mils..." class of argument doesn't
cut any ice.  What is critical is the rise time of the waveform.

Suppose you have a 100 Megahertz square wave clock:  Unless you have
a bandwidth above  20 times that the 'fiiltering' is going to stop it 
looking like a square wave.   OK HAPPY.  Kids stuff from first year.

But now you realise we are working with microwave freequencies.
I know from my days working in Silicon Valley for a "semiconductor firm
who shall be nameless" on military high speed LSI and ECL at these
speeds, the chip designers worry about transmission line effects.

Hey, these guys worry about the transmission line effects of power
surges on the power input line.  If you look, you will find many chips have
power feed on pins at the middle of the chip rather than at the end.

Now start facing some reality:  the signal doesnt travel along the conductor,
it travels in the gap between the conductor and the groundplane.  Where is
the groudplane on most chips ?  Somewhere a few tens of mills over there.
The length of the line is irrelivant under these conditions.

What zonks it all out of exitence is the dialectric (say he avoiding 
be Hegelian).  This is fairly grooty for microwave freqeuncies and so produces
significant wave dispersion.  This means wave form dispersion, and
differential speed of transmission with freqency.

Plop a signal along something short that looks like this and what hits the end,
never mind what bounces back out at you, doesn't look like the square wave
you shoved in.

------------------------------------------------------------

WHY WHY WHY is it that software bods and even the bulk of hardware bods
just don't realise you cannot ignore microwave effects, termination and the
rest when designing switching circuits ?   Even at the 5 MHz the noddy
micros run at these effects are noticeable.   At the 10 to 15 MHz of the
new 16 bitters they are starting to become significant.

FACE REALITY guys, or you'll go the way of FORTRAN.

/anton aylward