What is "Scattering Limit?" Vishay 1N914, 1N4148 datasheets - diyAudio
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Old 7th February 2012, 12:56 AM   #1
benb is offline benb  United States
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Default What is "Scattering Limit?" Vishay 1N914, 1N4148 datasheets

I was looking up datasheets to see what the difference between these two are (not a whole lot as this thread describes - I found it as I typed in the subject line and the DIYaudio board software found similar threads), and I found a Vishay datasheet that had the words "Scattering Limit" on several of the graphs, for both forward and reverse I/V characteristics, and of both diodes:
http://www.vishay.com/docs/85622/1n914.pdf
http://www.vishay.com/docs/81857/1n4148.pdf

What does this mean? The term appears on a line (if this means anything) at 20mA forward current, and 20nA (nanoamperes) reverse current.

This is apparently a Vishay-only term. I googled "scattering limit" signal diode and only found Vishay datasheets (even on datasheetarchive-style sites) in the results.

I googled the term generally, and found stuff on optics and Rayleigh scattering, but nothing that appears to apply to diodes. This is surely an insignificant term (to be sure, I did look at an NXP datasheet and saw no mention of it), but my inquisitive mind can't stand not knowing a term on a simple part's data sheet when I've been reading these things so long...

Last edited by benb; 7th February 2012 at 12:58 AM.
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Old 7th February 2012, 01:06 AM   #2
Bill_P is offline Bill_P  United States
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Scattering limit defines the normal production variation that is expected in the parameter on the graph.
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Old 7th February 2012, 01:44 AM   #3
benb is offline benb  United States
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Doh!
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Old 7th February 2012, 09:38 AM   #4
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Hmmm . . . looking at the actual spec values, I see max forward voltage of 1000 mV at forward current of 10 mA ("Electrical Characteristics" table, first line). But the associated "Typical Characteristics" graph (Figure 2) shows the forward voltage falling between the "scattering limits" of about 700 mV to 850 mV at forward current of 10 mA: significantly lower than the 1000 mV (max) spec value. If the upper "scattering limit" value of 850 mV really DID represent a production worst case, why publish a specification maximum of 1000 mV?

So I suspect a more correct understanding is something like, "In a normal production run, X% of the diodes will have forward voltages falling between 700 mV and 850 mV when forward current is 10 mA, but a few may be as high as 1000 mV.". Based on a few experiences with a manufacturing Incoming Inspection department, I'd make a SWAG that the "X%" of parts NOT falling between the scattering limits is probably no worse than 1% - maybe as low as 0.1 %.

Dale
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