Jim, I don't think you can without designing a much bigger circuit around the switch. Unless you simply disable the clock(s) before switching... There are special clock muxes designed to guarantee glitch-less operation though. ======================= Mikhail Matusov Senior Hardware Design Engineer Square Peg Communications Tel.: +1 (613) 271-0044 ext.231 Fax: +1 (613) 271-3007 http://www.squarepeg.ca ----- Original Message ----- From: "Peterson, James F (EHCOE)" <james.f.peterson@xxxxxxxxxxxxx> To: <si-list@xxxxxxxxxxxxx> Sent: Friday, May 30, 2008 10:03 AM Subject: [SI-LIST] Re: Quick switch > This is a little off the SI topic related to these FET switches, but I > would also want to understand how I select one of these clocks, by > enabling one these switches, without initially causing a sliver of a > clock pulse to propagate out to my flops. > > Jim Peterson > Honeywell > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Scott McMorrow > Sent: Friday, May 30, 2008 9:19 AM > To: steve weir > Cc: ravi.potana@xxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Quick switch > > Ravi > To follow on with what Steve has said, most FET switch packages do not=20 > have adequate package grounding. Since the substrate is normally=20 > grounded, this poses a problem, since there is parasitic capacitive=20 > coupling between each switch and the substrate. These are fairly easy=20 > devices to model in SPICE, and many manufacturers provide accurate=20 > models. IBIS models, however, cannot adequately model these devices. > > regards, > > Scott > > Scott McMorrow > Teraspeed Consulting Group LLC > 121 North River Drive > Narragansett, RI 02882 > (401) 284-1827 Business > (401) 284-1840 Fax > > http://www.teraspeed.com > > Teraspeed(r) is the registered service mark of > Teraspeed Consulting Group LLC > > > > steve weir wrote: >> An NFET or CMOS switch in a package has parasitics like any other=20 >> device. If you model and work within the limitations of those=20 >> parasitics you shouldn't have any unwelcome surprises. If you pretend > >> that the device is without parasitics you can easily make designs that > >> run into problems. >> >> Steve >> ravi.potana@xxxxxxxxx wrote: >> =20 >>> Hello All, >>> =20 >>> Please let me know if anyone has used Quick switch (FET based) on > clock >>> with frequency 125MHz for muxing operations and seeing any SI issues > on >>> the clock line after passing through the FET Switch.=20 >>> =20 >>> regards >>> Ravi >>> Please do not print this email unless it is absolutely necessary.=20 >>> >>> The information contained in this electronic message and any > attachments to this message are intended for the exclusive use of the > addressee(s) and may contain proprietary, confidential or privileged > information. If you are not the intended recipient, you should not > disseminate, distribute or copy this e-mail. 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