pick-and-place

That's just good beer and long lunch breaks at the fast food joint down the rud!

Jamie

Maybe he knew something others should know?

Sometime over design can be a killer.

Jamie

on for you, sheesh. Isn't the SRF of the 330nF 0603 rather low for bypass?

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is

ow as it translates directly into supported rise times and damping.

s in the case of power plane layouts. Looking into the parallel combination of capacitor and transmission line power plane, the capacitor diverts the high frequency current loading off the line thereby decoupling the bypassed device from other devices on the same power plane feed. This is only good within the working frequency range of the cap, so a 100KHz or a 1GHz SRF al most certainly does make a difference in that regard. Unless you're working at a few tens of GHz, there's no wavefront hitting capacitor, it is a lump ed element. That 330n with max 10MHz SRF is only slightly better than worth less. A 3.3n would do much better.

I leave that grunge work up to the mechanics like you....

That would be ECL with balanced output loading ... TTL was definitely a possibility, IIR the original TI recommended practices was something like one 0.1u per 10 ICs, nothing super critical.

I tend to assume that support and maintenance will be available until the check clears. Or, for expensive stuff like that, until the salesman gets his commission check. That way, I get to be happy when somebody actually supports their stuff (the rare case), rather than mad when they don't (the general case).

I found out the hard way that if you lose the hard drive in one of the Tek scopes that run XP, Tek will sell you a new hard drive for it (at inflated prices), but the new hard drive is blank. You have to have made the restore DVDs when it was new, just like a PC. I got around it because we had 6 of the same model, so I used the backup from another scope. I was worried about XP licensing and scope calibration issues, but everything came up and ran in spec. (I don't remember the exact model offhand, but it was new in 2008 or early 2009.)

I used a couple of filters on that picture to "see through" where you tried to blank out the name. Acme Inc, 1060 W. Addison.

At a previous job (in Kansas City), we were working with some guys from Los Angeles, and the "earthquakes vs. tornadoes" argument inevitably came up. The usual winning argument from the tornado side was "there's a siren that goes off 10 minutes before the earthquake gets there, right?"

Matt Roberds

Demand a refund.

It was classic TTL.

And the thinking, too.

At nanosecond speeds, you can reasonably treat a power:ground plane pair as a parallel-plate capacitor, with a small amount of inductance from the vias that you need to get at the planes from the surface.

At picosecond speeds, you can treat the unbypassed plane pair as a big, rectangular, fairly lossy transmission line. If you can access it through an embedded SMA test connector, it TDRs that way: a transmission line of an ohm or two, with weak, fuzzy reflections off the edges of the board. As you add bypass caps here and there, the structure starts looking almost like a perfect capacitor. Bypass cap SRF is not visible in the TDR measurement of plane impedance.

Here's the TDR of a power plane on an unpopulated board:

It looks a lot like a capacitor with 1.8 ohms of ESR.

On a multilayer board with decent power pours, almost any bypassing scheme works, which is why there are so many opinions. There's a lot of folklore left over from the days of double-sided boards without proper ground and power planes.

You are way too clever for me.

I grew up in hurricane country. Hurricanes kill a lot more people than earthquakes.

And now for the rest of the story...

Thank you Paul Harvey

caps in the case of power plane layouts. Looking into the parallel combinat ion of capacitor and transmission line power plane, the capacitor diverts t he high frequency current loading off the line thereby decoupling the bypas sed device from other devices on the same power plane feed. This is only go od within the working frequency range of the cap, so a 100KHz or a 1GHz SRF almost certainly does make a difference in that regard. Unless you're work ing at a few tens of GHz, there's no wavefront hitting capacitor, it is a l umped element. That 330n with max 10MHz SRF is only slightly better than wo rthless. A 3.3n would do much better.

Not exactly a counter-argument of high intellectual quality.

My irony meter just pegged. John Larkin's "thinking' is pretty much confine d to thinking that John Larkin is wonderful.

ion for you, sheesh. Isn't the SRF of the 330nF 0603 rather low for bypass?

nce

is

s.

know as it translates directly into supported rise times and damping.

caps in the case of power plane layouts. Looking into the parallel combinat ion of capacitor and transmission line power plane, the capacitor diverts t he high frequency current loading off the line thereby decoupling the bypas sed device from other devices on the same power plane feed. This is only go od within the working frequency range of the cap, so a 100KHz or a 1GHz SRF almost certainly does make a difference in that regard. Unless you're work ing at a few tens of GHz, there's no wavefront hitting capacitor, it is a l umped element. That 330n with max 10MHz SRF is only slightly better than wo rthless. A 3.3n would do much better.

Hello? It's just a 2-D charged transmission line. All that has nothing to d o with the ineffective low SRF (faux) decoupling caps preventing the high f requency switching currents from launching wave energy out onto the plane, and this at frequencies most likely to couple through the Vcc/Gnd points of the other ICs connected into the plane.

You don't get it, and you never will, but it doesn't matter since you don't design electronics.

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lation for you, sheesh. Isn't the SRF of the 330nF 0603 rather low for bypa ss?

edance does. And the impedance in the frequency range that mainly matters i s dominated by ESL, which is about the same for all 0603 ceramic caps.

to know as it translates directly into supported rise times and damping.

z or 500 kHz. The high-frequency impedance will be about the same.

ost any ole ceramic caps here and there.

he caps in the case of power plane layouts. Looking into the parallel combi nation of capacitor and transmission line power plane, the capacitor divert s the high frequency current loading off the line thereby decoupling the by passed device from other devices on the same power plane feed. This is only good within the working frequency range of the cap, so a 100KHz or a 1GHz SRF almost certainly does make a difference in that regard. Unless you're w orking at a few tens of GHz, there's no wavefront hitting capacitor, it is a lumped element. That 330n with max 10MHz SRF is only slightly better than worthless. A 3.3n would do much better.

interesting. I remember looking at the power planes as a transmission lin e. The effective impedance decreases with radial distance so the amplitude of the wave decreases as it spreads out and diminishes the need for decoup ling caps. But if there are a lot of chips on the board all clocking at th e same time I expect the power planes won't be enough for most designs.

ir as a parallel-plate capacitor, with a small amount of inductance from th e vias that you need to get at the planes from the surface.

, rectangular, fairly lossy transmission line. If you can access it through an embedded SMA test connector, it TDRs that way: atransmission line of an ohm or two, with weak, fuzzy reflections off the edges of the board. As yo u add bypass caps here and there, the structure starts looking almost like a perfect capacitor. Bypass cap SRF is not visible in the TDR measurement o f plane impedance.

o do with the ineffective low SRF (faux) decoupling caps preventing the hig h frequency switching currents from launching wave energy out onto the plan e, and this at frequencies most likely to couple through the Vcc/Gnd points of the other ICs connected into the plane.

't design electronics.

Everything suggests that it's John Larkin who doesn't design electronics - he just tinkers with stuff until it works. His enthusiasm for ignoring a ca pacitor's series resonant frequency (SRF) in favour of its equivalent serie s inductance (ESL) which he believes to be the same for all 0603 packaged c apacitors is indicative of his level of design insight. If you don't think hard about what you are doing you do tend to see things as a bit simpler th an they really are. Sadly, you can get away with it most of time - but I've spent quite a lot of time cleaning up after people who didn't.

it's not just a charged transmission line.

the dielectric is lossy and because the wave spreads in two dimensions the characteristic impedance drops proportional to time Does SRF matter? not if plane is absorbing most of the energy at those frequencies,

Synchronicity is a myth.

What I get is you don't know much about circuits...but nothing you do is of any concern to me.

Far be it from me to interfere with this lovely intercontinental flame war, but do you have any actual data that suggests that there's a significant difference between 0603 caps mounted on boards? I sure would like to know about it, if so.

IIRC JL has done a bunch of measurements of that sort of stuff, including things like mounting termination resistors upside down, which reduces the inductive discontinuity considerably.

A parallel plate geometry fed from a point isn't a transmission line, because it isn't translationally invariant. It's more like a tapered impedance transformer, where the matching impedance keeps dropping as you go further from the source. So if it's 1 or 2 ohms at the source, the amount of bounce at distant points is going to be very small.

The SRF of a capacitor is only important in the neighbourhood of the resonance, where (being a series resonance) it _improves_ the bypassing. A series LC's impedance is symmetric when its magnitude is plotted against log(f)--if it's a good bypass at SRF/10, it's an equally good bypass at 10*SRF.

Once you get above a few times SRF, it's only the inductance that matters, because

|Z| = |wL-1/wC|

By the time you get to 3*SRF, X_C is only 1/9 as large as X_L, so the impedance is only 10% below what you'd predict from inductance alone.

And, remember, that at that frequency it's as good a bypass as it is at SRF/3.

Cheers

Phil Hobbs