BJTs as ultra low leakage protection diodes

Jun 12, 2009 70 Replies
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We are talking about parts that were designed 40 years ago. The RCA COSMOS process was not dense enough to use MOSFETs for protection devices (couldn't fit 6 more on the chip), so they used zeners. No doubt they felt comfortable with that because of experience with their consumer bipolar ICs that had on chip zener regulators.

Also, they did not bother with "representations". If you look at die photos of old RCA parts like the 4000A series, they match the datasheet schematics.

Of course it's likely that second sources changed the protection circuits (don't they always mess with them?).

-- David DiGiacomo, San Francisco, CA snipped-for-privacy@slack.com

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P

Well, we Norwegian Blues stun easily. ;)

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
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=A0 =A0 =A0 ...Jim Thompson

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=A0 =A0 ...Jim Thompson

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A lot of times you just plop in an "off" transistor when a diode would do, simply to get past layout verification tools.

Occasionally you see this done with a P-FET do discharge a node using a parasitic diode from the positive rail.

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J

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Yep. An NMOS, gate to ground thru a resistor, source to ground, drain to pin.... sometimes fancier gimmicks.

I have seen 10-15 device structures for protecting outputs when they are configured as tri-state-when-unpowered ;-)

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
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J

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Forgot a point, seen only recently... a special schematic symbol that describes layers to satisfy the LVS.

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
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F

Jim Thompson a écrit :

Why the resistor?

Thanks, Fred.
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J

Rise-time dependent clamping.

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
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R

datasheet

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The protection diodes shown are between inputs. Related to inputs, note those to the substrate (V-) and if implemented, those to the supply are most definitely not shown. For both digital and analog devices, note protection diodes to the substrate are not shown. And diodes to the supply (if added) seem to be almost state secrets..

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J

datasheet

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There's a good OP27 model on my website... one I did in the early '90's.

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Obama... Recklessness Cloaked in Righteousness
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J

I'm not sure how other people's brains work, but mine is some sort of massively-parallel possibility generator, followed by a does-it-make-sense filter--cultivated over time--then some I/O.

At least that's its creative process. Possibly related to the left-handed, quasi-ambidextrous thing--that changes brains.

Thoughts aren't in any spoken language, but in some sort of parallel machine language where multiple ideas fire in 300mS, which, if interesting, are sampled / latched in snapshots, separated, sorted, parallel-to-serial converted, then translated into language for expression.

Lots of times the thinking parts sit back and listen, amused, while the talking part spools output.

Talking fast enough to voice the chaos is impossible by factors.

The filter's the difference between madness and sanity.

Weird, huh?

Cheers, James Arthur
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J

Yes. There seems to be some massively parallel idea generator that can be carefully primed and then let loose. It definitely runs subconscious, background, often during sleep. It's not quantitative but can make some pretty good guesses.

Why work at designing when you can do it painlessly in background?

I suspect that DNA designs, say, antibodies by a similar algorithm, some sort of massive, random set of cross-correlation experiments.

John

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