A look inside the DS3231
On Sun, 30 Jul 2017 12:23:17 +0200
Pete Stephenson pete@heypete.com wrote:
- 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.
There are multiple optimization points. One is to select a prodcution
process that is optimized for low leakage. I.e. thick gate oxide
and high threshold voltage. Both of these parameters imply higher
suplly voltage.
Then, in the design, you make your transistors long and large.
The problem here is, that power consumption scales proportional
to the square of supply voltage, the gate capacitance and the
switching frequency. This means, if you choose a low leakage
process, and thus high supply voltage, your power consumtion
will go up. The same goes for choosing large transistors.
Hence it becomes a trade-off between static (leakage) and
dynamic (through gate capacitance) power consumption.
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 a rule of thumb, you can assume that in an "old" (aka large node size)
process the gate capacitance is approximately 1nF per mm^2. So, you can
build quite easily 10-100pF of capacitors on-chip.
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
On the subject of low-current 32kHz oscillators:
DS3231 spec says typical 1uA for timekeeping and circa 600uA for
temperature conversion. I understand they periodicailly kick the
temperature conversion on but only for extremely short duty cycles and this
is included in the 1uA.
Standard DS12887 spec was 500nA with the oscillator and counter logic
running. This did not have any temperature conversion/compensation.
RCA published a 4007-based 32kHz oscillator that was circa 1uA but I think
that spec was at 1.5V. RCA got a patent on putting a resistor in the drain
of the first stage to slow it down and reduce power consumption to get down
to 1uA. So in the DS12887, Dallas figured out how to go at least a factor
of two lower in power. I would imagine there's a series of patents by watch
companies on this subject as well probably all back in the 1970's and
1980's.
Tim N3QE
On Sat, Jul 29, 2017 at 2:32 PM, Pete Stephenson pete@heypete.com wrote:
On Thu, Jul 27, 2017, at 09:46 PM, Trent Piepho wrote:
Looks like it still says "DALLAS SEMICONDUCTOR" to the left of Maxim.
Maybe Maxim only wanted to change the mask enough to find some empty
space to sign it?
It does indeed say "DALLAS SEMICONDUCTOR".
I managed to get some high-quality photos using the microscope's
on-board camera and have updated the photo album at
https://imgur.com/a/0zudj with the newest ones (they're the
all-rectangular photos below the two circular photos). There's some
high-resolution composite images.
Some things I found interesting:
-
There's a section just above the "Maxim" part that has several
snippets of text ("17A3", "16A3", etc.). In normal light, each of these
bits of text is a different color, where the colors correspond to
different layers of the chip. Each bit of text has a different depth of
focus, indicating they're physically closer or further from the lens.
Does anyone know what material the colors might correspond to? -
There's several square grids of circles-in-squares circuit elements. I
have no idea what these are. -
I find it remarkable that this circuit can operate on less than a
microamp during normal usage, including temperature conversion.
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"?
Cheers!
-Pete
--
Pete Stephenson
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On Sun, 30 Jul 2017 08:15:57 -0400
Tim Shoppa tshoppa@gmail.com wrote:
I would imagine there's a series of patents by watch
companies on this subject as well probably all back in the 1970's and
There are also a lot of papers and books. I can recommend those
written by Eric Vittoz, who was the mastermind behind quite a
few of the oscillator circuits of the Swiss watch industry.
In particular his book on low power oscillators[1]. He also
wrote a review of the history of low power electronics in
the watch industry about 10 years ago[2], which is also very
much worth a read.
Attila Kinali
[1] "Low-Power Crystal and MEMS Oscillators", by Eric Vittoz, 2010
[2] "The Electronic Watch and Low-Power Circuits", by Eric Vittoz, 2008
https://doi.org/10.1109/N-SSC.2008.4785777
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
That device also has analog circuitry for the oscillator itself and the
temperature sensor and the temperature compensation.
I believe I have read an app note some time ago, it may have been from
Maxim describing a kind of ring oscillator being used as a temperature
sensor which drew much less power than a bandgap or a PN junction and
directly produced a digital output.
The DAC itself, or whatever circuit they use for temp compensation also has
analog components and must use pico power.
Quite amazing.
On Jul 30, 2017 7:13 AM, "Attila Kinali" attila@kinali.ch wrote:
On Sun, 30 Jul 2017 12:23:17 +0200
Pete Stephenson pete@heypete.com wrote:
- 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.
There are multiple optimization points. One is to select a prodcution
process that is optimized for low leakage. I.e. thick gate oxide
and high threshold voltage. Both of these parameters imply higher
suplly voltage.
Then, in the design, you make your transistors long and large.
The problem here is, that power consumption scales proportional
to the square of supply voltage, the gate capacitance and the
switching frequency. This means, if you choose a low leakage
process, and thus high supply voltage, your power consumtion
will go up. The same goes for choosing large transistors.
Hence it becomes a trade-off between static (leakage) and
dynamic (through gate capacitance) power consumption.
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 a rule of thumb, you can assume that in an "old" (aka large node size)
process the gate capacitance is approximately 1nF per mm^2. So, you can
build quite easily 10-100pF of capacitors on-chip.
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
time-nuts mailing list -- time-nuts@febo.com
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mailman/listinfo/time-nuts
and follow the instructions there.
On Sun, 30 Jul 2017 08:53:51 -0500
Didier Juges shalimr9@gmail.com wrote:
I believe I have read an app note some time ago, it may have been from
Maxim describing a kind of ring oscillator being used as a temperature
sensor which drew much less power than a bandgap or a PN junction and
directly produced a digital output
Right. I always forget that there are these "digital" sensors
that are much less power hungry than the "analog" ones.
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
[blast from the past…]
Attila Kinali writes:
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.
The die micrograph shows one clearly identifiable classical 8:1 bandgap
circuit in 3x3 configuration in the lower left corner of the die plus
three more instances of bipolar transistors (3x3, 3x2 and 4x2
configuration) that might be used as additional temperature
compensation.
Regards,
Achim.
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
Waldorf MIDI Implementation & additional documentation:
http://Synth.Stromeko.net/Downloads.html#WaldorfDocs
Well, time and technology move on.
As wonderful as the DS3231 is, there is a newer chip from Micro Crystal
that is smaller, more accurate than the DS3231M, much cheaper, and draws
less power.
Micro Crystal is the Semiconductor division of Swatch (Swiss Watch Company)
If this sort of thing interests you, look at the
https://www.microcrystal.com/
https://www.microcrystal.com/en/products/real-time-clock-rtc/
https://www.microcrystal.com/en/products/real-time-clock-rtc/rv-3028-c7/
The RV-3028 is 3.2x1.5 mm in size, 1.5ppm, additionally trimmable, 45 nA
standby current, under $3 USD in price and in stock at Mouser and Digikey.
Of particular interest to me, besides all the normal features, this one
also directly keeps time in Linux Epoch time, seconds and fractions since
(your choice of epoch) so smaller data movements on the bus, and I don't
have to keep converting back and forth between time formats/structures.
--- Graham
==
On Sun, Apr 19, 2020 at 8:03 AM ASSI Stromeko@nexgo.de wrote:
[blast from the past…]
Attila Kinali writes:
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.
The die micrograph shows one clearly identifiable classical 8:1 bandgap
circuit in 3x3 configuration in the lower left corner of the die plus
three more instances of bipolar transistors (3x3, 3x2 and 4x2
configuration) that might be used as additional temperature
compensation.
Regards,
Achim.
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
Waldorf MIDI Implementation & additional documentation:
http://Synth.Stromeko.net/Downloads.html#WaldorfDocs
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On Sonntag, 19. April 2020 16:04:39 CEST Graham / KE9H wrote:
The RV-3028 is 3.2x1.5 mm in size, 1.5ppm, additionally trimmable, 45 nA
standby current, under $3 USD in price and in stock at Mouser and Digikey.
Of particular interest to me, besides all the normal features, this one
also directly keeps time in Linux Epoch time, seconds and fractions since
(your choice of epoch) so smaller data movements on the bus, and I don't
have to keep converting back and forth between time formats/structures.
That's all good, but that datasheet you linked to says it's not temperature
compensated at all?
Regards,
Achim.
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
Samples for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldSamplesExtra
Achim:
You are right. I missed that.
You need to go to the RV-8803 to get temperature compensation, but then you
loose the Epoch timer I wanted.
--- Graham
On Sun, Apr 19, 2020 at 5:21 PM ASSI Stromeko@nexgo.de wrote:
On Sonntag, 19. April 2020 16:04:39 CEST Graham / KE9H wrote:
The RV-3028 is 3.2x1.5 mm in size, 1.5ppm, additionally trimmable, 45 nA
standby current, under $3 USD in price and in stock at Mouser and
Digikey.
Of particular interest to me, besides all the normal features, this one
also directly keeps time in Linux Epoch time, seconds and fractions since
(your choice of epoch) so smaller data movements on the bus, and I don't
have to keep converting back and forth between time formats/structures.
That's all good, but that datasheet you linked to says it's not
temperature
compensated at all?
Regards,
Achim.
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
Samples for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldSamplesExtra
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