Long term drift of voltage reference is unknown, can we guess?

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This isn't actually correct. It depends on the design of the bandgap, but sure, the bog standard topologies you see in all the main references are not that great.

For example, LT has a "low noise" voltage ref LTC6655 which quotes around

50nv/sqrthz flatband noise with an IQ=5ma, at 2.5V output

I have designs in production that can do that in around 60ua. Which, on the basis of noise going with the sqrt of current, means something like 5,000 times better performance.

One needs to throw away all the legacy approaches like Brokow. They are all, essentially, Micky Mouse techniques. I have no idea why the likes of Analog Devices and LT haven't moved on with more sophisticated designs.

The general ideas are floating about in the literature, but there are a several important tweaks needed to get them to be really good in practice. Unfortunately, I cant really post them for obvious reasons, but I will say I need 100dB PRS at 200mV dropout, not the usual lying Vout + 1V often quoted on data sheets.

-- Kevin Aylward

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Kevin Aylward
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I didn't know that there were that many fabs... Have you sign on with 22 of your split personalities?

-- Kevin Aylward

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The original (uA723 from Fairchild) spec'ed 0.1 % per 1000hr typical, while the National Semiconductor clone (LM723) claims 0.05% per 1000hr typical (there's room for lots of uncertainty

But those aren't TTL transistors, it's a 40V process. It might be as simiple as some guard rings at the surface to make a subsurface breakdown in that case, or an extra 'moat' diffusion. The process was complex enough to make (according to the Fairchild schematic) PNP, NPN, and NFET.

And a few metrology holdouts still maintain stacks of mercury batteries.

If you want to make a case for EE requiring knowledge of chemistry, this kind of thing does it. The noise depends on teensy amounts of contaminants around the edges, and using the wrong wetting agent in midprocess will kill ya. Fairchild, I've heard, shut down for a few weeks when Joy introduced 'Lemon Fresh".

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whit3rd

I have accounts with all the obscure SE Asia and European secondary and tertiary sources to the majors... as well as _all_ the majors.

It's easy to get PDK kits if you have a history of generating business. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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I even have one that _only_ does an ancient 30V bipolar ;-) ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Jim Thompson

te:

a 4% initial tolerance spec

ors (Beginning of Life)

he drift after 10 years

drift from the numbers supplied?

yone here got insights?

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tion note

It would help to differentiate you from Dan.

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Bill Sloman, Sydney
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bill.sloman

The designers had *much* better ones, even 17 years ago when I worked there, for use buried inside asics. I'm not sure why the ones sold as standard products were not so great (at least last time I looked). Maybe the marketing people in that particular product line didn't know that people would want such a thing or that it was feasible, because no competitor offered it. (And I bet the same situation occurred at the competitor company.)

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Chris Jones

It may be that they just cant get the staff nowadays :-)

Its crucial, somewhat ironically, to have low noise, low power, low voltage references, in the OCXO ASICs I design. 5ma would be way too much, despite the chip using 100s ma on cold. Its because the oven heater regulation will drop out too early with ambient temperature. Typically the xtal is cut for

90 deg internal operation, but needs to operate at 85 deg external temp. 5ma generates a lot of uncontrollable standby heat .

-- Kevin Aylward

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