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