[time-nuts] A look inside the DS3231

Attila Kinali attila at kinali.ch
Sun Jul 30 05:15:35 EDT 2017

On Sat, 29 Jul 2017 20:32:30 +0200
Pete Stephenson <pete at heypete.com> wrote:

> - There's several square grids of circles-in-squares circuit elements. I
> have no idea what these are.

If you look closely, these are actually suqares-in-squares.
I am not sure, but my guess would be that these are the
capacitor banks for the correction of the oscillator frequency.

> - I find it remarkable that this circuit can operate on less than a
> microamp during normal usage, including temperature conversion.

That's not so remarkable. If you make the transistors long, then
you get very low leakage. Couple that with small clock frequency
and you use very little current. Modern ICs only use so much current
because they have so many transistors, which are also optimized
for being fast, rather then low leakage. 

> The DS3231 has on-board temperature monitoring to correct the crystal
> frequency: is this something where they would have bothered putting a
> separate sensor next to the crystal itself, or are the die and the
> crystal are close enough and in the same package that they could use an
> on-die sensor like a diode and call that "good enough"?

My guess would be that it's a PN-junction or a bandgap temperature
sensor somewhere on the chip. Adding another part increases the cost
of production quite considerably.

			Attila Kinali

You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor

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