Xref: utzoo comp.arch:17453 sci.electronics:13248 sci.physics:13849 comp.lsi:1114 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!aglew From: aglew@oberon.crhc.uiuc.edu (Andy Glew) Newsgroups: comp.arch,sci.electronics,sci.physics,comp.lsi Subject: Re: Electro-optic bus Message-ID: Date: 1 Aug 90 02:11:32 GMT References: <1985@trlluna.trl.oz> Sender: usenet@ux1.cso.uiuc.edu (News) Distribution: comp Organization: University of Illinois, Computer Systems Group Lines: 45 In-Reply-To: aduncan@rhea.trl.oz.au's message of 31 Jul 90 23:28:48 GMT >>>A laser might not be the best - they have a delay from zero curent... > >Depending on area etc it can be up to 10 ns for lasers. LEDs are a >little quicker. Thanks for providing the ballpark number! Now, is that just the time for the electro-optic conversion? Does anyone have any ideas what the latency for reception by a native Si optic->electronic receiver would be? Especially taking into account the time to amplify from whatever signal levels the optical receiver produces, to normal Si logic levels? Let me do some informal calculations (mainly to prompt people who know better to correct my (mis)estimates): Say it's 5ns for the electro-optic latency. Say another 5ns for the reception and amplification to CMOS levels. Add 1ns for transmission time in the optical medium Add another 4ns for the point-to-point electrical interconnect. That gives maybe a 15ns latency. Well, that's nothing great... you never go wrong building a low-latency interconnect, and electronics can do better than this. How many signals could be crammed onto this 15ns latency electro-optical star? -- Andy Glew, andy-glew@uiuc.edu Propaganda: UIUC runs the "ph" nameserver in conjunction with email. You can reach me at many reasonable combinations of my name and nicknames, including: andrew-forsyth-glew@uiuc.edu andy-glew@uiuc.edu sticky-glue@uiuc.edu and a few others. "ph" is a very nice thing which more USEnet sites should use. UIUC has ph wired into email and whois (-h garcon.cso.uiuc.edu). The nameserver and full documentation are available for anonymous ftp from uxc.cso.uiuc.edu, in the net/qi subdirectory.