It doesn't get any better than this, as explanations can go. Thank you! But nonetheless many thanks also to every other that replied. Cheers, Mario At 03:47 2017-12-03, Sean Breheny wrote: >I like the decoupling tutorial page which Byron linked to. I also did a >little LT Spice simulation to illustrate the difference which decoupling >makes. > >This simulation is based on the 74HC series output cell model given at the >end of this library: >https://www.classe.cornell.edu/~ib38/teaching/p360/lectures/wk12/l35/1 >1.1/74hc.lib > >The simulation is for a single 74HC series type output cell which is >roughly similar to what would be at the output of your oscillator. The >simulation has 100nH of inductance between the Vdd pin and true 3.3V, and >100nH between Vss and true GND. This represents about an inch of typical >PCB trace. The pulsed source inside is supposed to simulate the internal >oscillator circuit and is therefore referenced to the local internal Vss >net of the chip. I have given it a 15pF load which is the output load give= n >in the oscillator datasheet as typical. I show a 10MHz output. For many >cmos devices, the output stage dominates the pulsed load from the power >supply since it drives a much larger capacitance than internal nodes do. > >Here's the simulation with only stray capacitance (10pF) as the bypass >capacitance: > >https://s8.postimg.org/niw5n96at/Screenshot_from_2017-12-02_21_33_24.png > >The green trace is the output waveform and the blue is the local Vdd-Vss >difference seen by the other internals of the chip. The ringing caused by >the pulsed supply current drawn from the rails interacting with the stray >inductance and capacitance is about 1.5V peak which could be enough to >cause glitches or other disturbances to the internal circuitry. > >Here's the result with a 100nF bypass capacitor directly across Vdd, Vss: > >https://s8.postimg.org/l1keg3had/Screenshot_from_2017-12-02_21_34_06.png > >The ringing and ripple has almost disappeared from the power rails and the >output of the oscillator is cleaner, too. > >Sean > > > >On Sat, Dec 2, 2017 at 7:40 PM, Byron Jeff wrote: > >> Comments embedded inline... >> >> On Sat, Dec 02, 2017 at 07:18:48PM +0100, Electron wrote: >> > >> > Hello, >> > it may seem a banal question, but as it's the first time I use an >> external >> > oscillator (with integrated crystal), I am not sure. The datasheet mak= es >> no >> > mention whatsoever to the need to use a bypass capacitor in the power >> line: >> > >> > https://global.kyocera.com/prdct/electro/product/pdf/clock_k_e.pdf >> > >> > But is this truly the case? >> >> Yes. The requirement is so prevalent that it's seldom explicitly mention= s. >> >> > >> > Should I put a (100nF?) bypass capacitor anyway in your opinion? >> >> Always. This tutorial discusses why it is needed, choosing appropriate >> values, and different types of noise management and isolation: >> >> http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html >> >> > >> > Space on the board may be used for something else otherwise, so I don'= t >> > want to put useless components. But then again who does. >> >> Never useless. >> >> > >> > Also, I guess there's no advantage in grounding the metalcase on this >> > integrated oscillator, like I use to do with Xtals. Maybe it's already >> > grounded but I haven't received it yet.. I ask in case it's not. >> >> Generally a canned oscillator will have a ground lead. So it's not >> necessary so add an additional one. >> >> > Thank you. >> > Kind regards, >> > Mario >> >> No problem. Hope this helps, >> >> BAJ >> -- >> Byron A. Jeff >> Associate Professor: Department of Computer Science and Information >> Technology >> College of Information and Mathematical Sciences >> Clayton State University >> http://faculty.clayton.edu/bjeff >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >--=20 >http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .