Hi,
@ macrohan : Cool !! You got the funda...
@ smarty : Quote: I have started on an cross coupled vco with the tail source replaced with an simple resistor ( nmos device).
Passive components always provide better phase noise profile than corresponding active components, mainly because flicker noise is linherently less in a resistor than a MOS Transistor.
Quote:I would like to know if people use resistor rather than the tail source, to improve phase noise of the vco.
No, i dont think so....People still prefer tail current source as it provides -ve Impedance [ -1/Gm ] control.
@ Dr. Iorga : I agree Gnd Bounce will couple directly if you place a R-C Filter like the once shown in figure. But I beleive inspite of a nearby M-S cktry, a STAR routing + a separate LDO from the PMU [ which usually comes with a large external cap b/w vdd & gnd rails] should take care of that....So Gnd Bounce shouldn't be that big a problem.
Also, wouldn't the cap prevent the effect of Gnd Bounce by creating same variation on both gate & source & keeping vgs constant ?
Acc. to me, this cap will prevent effects of Gnd Bounce & increasing high-freq. gnd rail PSRR.
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Mayank.