According to most capacitor manufacture datasheets the impedance vs freq plots of a 1uF X7R vs a 10nF X7R are equal for frequencies above resonances. So I wonder if there are problems using one large 1uF ceramic in place of the traditional arrangement of a tantalum in parallel with a small value ceramic for bypassing purposes ?
Adam.
"Adam S"
** Murata don't think so:Any day you can avoid using a tantalum cap is a good day.
....... Phil
Why dont you put some "accurate" spice models of the manufacturers capcitors in to a Spice simulator and see how they react to transient and frequency inputs.
Here! Yageo have the spice models and simulator.
JG
"above resonances"? A capacitor is an inductor above resonance, so any plots up there are rather useless. Also misleading, as the resonant frequency is going to be different in your circuit than in any other, or test, circuit.
I'd make up a little test jig, with a noisy IC, say a 74F161 toggling at 50MHz, a HF scope to BNC coax line soldered right to pins 7 and 14, and various capacitors I can plonk onto those pins.
"Ancient_Hacker"
** Complete bollocks.** The ( series) resonant frequency shown is that of the cap alone - f****it ** You can do a little jig on your head for all anyone here cares.
...... Phil
Not so... in many cases operating capacitors above their self-resonant frequency is useful.
This is true for pretty much any simulation vs. a built-up PCB; the devil is always in how much the difference is.
Pls answer these questions:
(1) In a series LC circuit, below resonance the reactance is: ( capacitive, resistive, inductive )
(2) At resonance the reactance is: ( capacitive, resistive, inductive )
(3) At above resonance the reactance is: ( capacitive, resistive, inductive )
(4) If you want a capacitor, use a ( capacitor, resistor, inductor )
(5) If you use an inductor in place of a capacitor, you are a: (winner, drone, loser )
The obvious answer being to use an inductor above its SFR :-)
-- Thanks, Fred.
Uh, won't there be the slightest amount of leakage at dc?
-- Many thanks, Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com Please visit my GURU\'s LAIR web site at http://www.tinaja.com
Haw!
Actually, I glommed onto a bunch of "Genoformers" which curiously measured as capacitors on my LC bridge at 1000 Hz. Turned out they were transformers designed to pass seismic signals, so 1000Hz was way above their SRF.
Capacitor. However, once you get past EE 101 designs, you find that there are plenty of cases where you can't get a single capacitor that behaves reasonably close to an ideal capacitor over the design's intended operating range.
Having to with deal with the reality of doing more complex designs than you do?
Interested in testing out a gyrator?
Hear hear.
I had to do a very systematic approach to a number of InfiniBand boards I designed. Without going into detail, let's just say there were a _lot_ of frequencies of interest that had to be appropriately decoupled.
No one size or type of cap will span the decoupling requirements on a reasonably complex board; one chooses various caps to implement specific parts of the decoupling requirements. I also used some inductors, of course - there are times for them; and all that doesn't incude the power system ;)
Cheers
PeteS
"Ancient_Hacker"
( snip all the asinine drivel)
???????????
........ Phil
Have you bonked Lyn(n) yet?
DNA
I won't call that leakage, but I think I added a smiley :-) Here's another one :-)
-- Thanks, Fred.
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