John, If you are talking about a clock generator IC or a clock oscillator module then YES, the clock output of those is a buffer with some driving capability. They usually have a spec to be capable of (!) driving a certain capacitive load. I see a lot of engineers getting confused by these spec's as if you need to add the capacitive load as a form of termination. This is not the case! A common spec for a clock output would be 15pF. The original meaning of the 15pF simply is a fan-out of 5 with an average input capacitance of 3pF. I guess this is from the days of 2 micron CMOS. ;-) If you need to design or test a clock driver, not knowing where or how it will be used then you will have to stick to the spec, load it with 15pF or whatever spec'd and verify the properties. Of course if you know the exact loading of the clock output then try to model this specific load as accurate as possible. Do not add a capacitor on a clock output because it is spec'd to drive a certain capacitive load. Eddy Fremont CA www.phaselink.com --- john smith <pranksteroma@xxxxxxxxx> wrote: > > Hi Guys, > Is the 'clock signal' driven by a buffer? > > Why do we use capacitors as loads, wont they load > the driving ckt like > resistors? > > And in hspice does the simulator automatically > connect an infinite resistor > to open ends? > > Thanks, > JS ____________________________________________________________________________________ Yahoo! oneSearch: Finally, mobile search that gives answers, not web links. http://mobile.yahoo.com/mobileweb/onesearch?refer=1ONXIC ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu