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From: flower@hpcc01.HP.COM (Graham Flower)
Newsgroups: sci.electronics
Subject: Re: ECL logic computers ?
Message-ID: <4450010@hpcc01.HP.COM>
Date: 27 Jun 91 17:01:53 GMT
References: <7183@gara.une.oz.au>
Organization: HP Corp Computing & Services
Lines: 38



     ECL is used in a number of computers. The design tools are there but it
     is true that they are behind the CMOS tools. ECL is easy to get to 500Mhz.
     It willl easily go much higher. I have personally designed circuits that
     clock at over 6 gigaherz and ECL circuits that have clock rates as high as
     10 gigaherz have been built. However at about a gigaherz life becomes 
     more complicated due to bond wire inductances and package parasitics. 
     To work above 1 gigaherz is no big deal but right noe there are no standardd
     cheap packages that will make this stuff affordable for computers. This  
     will change. Computers will see alot of bipolar and bicmos in the future 
     as speeds require it.  Computer communication will be an area where data
     rates will have to be high and is a prime candidate for bipolar or GaAs.
     Right now there are a bunch of people from 5 or 6 companies working on 
     this (hp is one ). 

     Another issue and probably the biggest reason for less ECL in computers
     is the power dissipation of ECL. It is literally orders of magnitude 
     larger than CMOS. This means that you really cannot build a million 
     transistor chip in bipolar because the power is too great. Power       
     has limited bipolar chips to 10000 gates or so until recently. People
     are now doing 50000 nor so. CMOS can do 10-100 times the gates with less
     power. Bipolar tends to stay with the extreme performance types of
     computers. IBM uses it in alot of mainfraimes especially were speed is
     an issue. These computers are usually liquid cooled using pretty 
     interestin and innovative schemes which are far too expensive for a PC.
     CMOS is easy to systemize into design libraries and it is easier to 
     use with automatic layout tools. Fewer mask steps means high yields
     and quick turnarounds. Bipolar can do mixed functions and analog better,
     but for low cost, quick turn system applications like PCs it cant 
     touch CMOS. Bipolar is harder to systemize for digital. ECL is notorious
     for osillating if you are not careful on chip. Usually it is driving
     too large of a capacitive load that hammers you. 

     graham flower
     Hewlett Packard
     San Jose
     graham@hpmsdpo.sj.hp.com