Speaking on Decoupling Caps (this is like an "Which is the BEST Oil Thread 
on my Motorcycle Groups", just keeps going),

In the late 80's I worked for Philips Ultasound Corp.  We had the best HP 
Impedance analyzer money could buy!

I could not believe how good those cheap (OK , inexpensieve) 1uf 
Electrolytics were as far a ESR!
Yes the ones from Digikey and Mouser, like 1uF/50V.

I bitched about buying standard run of the mill capacitors for a machine 
that had high power drivers for the Ultrasound Tranducers.  Everything was 
very critical, to image, the bandwidth of our array drivers was from about 
700Khz all the way to 14 Mhz.  These driver modules ended up being ceramic 
hybrid modules made in Israel.  Lots of individual FET drivers, because of 
the focusing of the ultrasound transducer.  Lots of noise!
Hey, the best part was when we had demo in the lab at looking at babies in 
mom, facinating!

The .1uf ceramics were going down in impedance until about 100Mhz, would dip 
(bottom out) and start up because of lead and self inductance.  We soldered 
everything to copper pcb with no lead length to clamp in the analyser.
I wish I could remember the exact numbers, but in the mili ohms, often a 
cheap electrolytic would really supprise.

So a .1uf in parallel with the electrolytic did well.  Of couse, lots of 
Spicing, and a really good Analog Engineer was the key.  Not me, another 
retiree!

I never got to work for many places that had the instruments and gave you 
the time to do such tests.

I think PCB layout was much more important than the problems we had with 
components?

But that is just another opinion from a real old fart!

Mikey, remembering the HP Impedance Analyzer with fond affection!



 

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