On Sun, Jul 30, 2017, at 11:15 AM, Attila Kinali wrote: > On Sat, 29 Jul 2017 20:32:30 +0200 > Pete Stephenson <p...@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.
True, the larger ones are squares-in-squares, but the smaller ones to the left look like circles-in-octagons, but I find it hard to see the details of the smaller features. Either way, I should probably stare less through microscope eyepieces. It seems to stress the eyes a bit. > > - 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. Good point! I admit the details of optimizing transistors for different purposes is beyond my ken, and I appreciate the insight. > > 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. Indeed. At first glance, I was surprised not to see tiny discrete capacitors within the chip package itself, as I assumed (incorrectly) that getting sufficient capacitance to steer a crystal a little would require larger capacitors than could be easily put on a die, but then I remembered that each LSB in the aging register only changes the frequency by 0.1ppm at 25C, so that wouldn't need a large amount of capacitance. As you say, minimizing part count keeps the price down and makes the design simpler. Cheers! -Pete -- Pete Stephenson _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.