Folks,
How many of you had experience with semiconductor products, where the product performance significantly deviated from the datasheet. Many a times, the manufacturer cuts corners in the product test cycle and arrive at specs which are half baked.
Relatively few, and some were caused by poor implementation on our part. But, I can remember a few.
We bought a bunch of digitally-controlled silicon delay lines. They had a bunch of distributed silicon delay elements in a 1-2-4-8-etc pattern, and you could cut in the various length delays
with an 8-bit TTL input. They were spec'ed to have just a couple percent tolerance. Well, some of the chips didn't work at all, some of them were amazingly far out of tolerance, like +/- 25%
or worse, some drifted badly after a day, etc. I think the whole project got trashed because these things didn't work.
We built a 32-channel constant fraction discriminator, that consists of 2 comparators and a little logic to trigger when both comparators are tripped, for each channel. Well, I picked some jellybean single-element CMOS gate and FF chips to do that logic. There was a huge problem with switching noise contaminating the whole board. After much tribulation, I set about to measure the switching noise.
With a minimal series resistor on the isolated power islands for each channel, I measured the shoot-through pulse of the logic at something like 3 A for 3 ns. This was a very approximate measurement due to parasitic inductance, but gave an order of magnitude indication of where the problem was. I ended up completely redesigning the board with all different components, but I found some NXP gate chips that were touted as having a VERY small "equivalent gate charge", and with the same setup, I was not able to measure ANY transient pulse on the Vcc supply!
Those are two that come to mind immediately.
Jon