A look inside the DS3231
Hi all,
A few days ago I reported the results from letting a DS3231 RTC run for
a year, and how the chip kept time well within the published specs.
Since I had acquired several DS3231s from dubious sources (Asian vendors
on a major auction site) as part of an RTC module that fits on the
Raspberry Pi's header pins, I was doubtful of the authenticity of the
chips. I decided to sacrifice one in the name of science and decapped it
at home using alternating heat (a lighter) and cold (a glass of cold
water) to embrittle the epoxy casing, then sanded down the back of the
chip on fine-grain sandpaper to expose what I hoped was the back of the
internals (so as not to damage the die itself).
Other than inadvertently sanding through half of the crystal's housing,
thus breaking one of the forks of the crystal, this was a success. (I
was prepared to decap one in acid had my attempt at physically removing
the epoxy package failed.) I slightly scratched the die itself while
separating it from the epoxy, but the die itself is clearly visible.
Based on a sample size of one and the markings on the die itself, it
appears the chip is authentic. The markings on the outside of the epoxy
package look a bit dubious and not like typical Maxim laser-markings, so
it's possible the chip was re-labeled at some point. I'll contact Maxim
to see if they can look up the lot information.
I used my 2 megapixel USB microscope to take some images throughout the
process that you might find interesting. The microscope has limited
resolution, particularly at high magnification, so some of the photos
may not be perfectly clear. I have access to a Zeiss petrographic
microscope at my work and will see if I can get some better images
tomorrow. I'll try to get high-quality images of the whole chip and
stitch them together into a larger composite.
Anyway, the photos are available at http://imgur.com/a/0zudj -- I will
add more photos from the petrographic microscope tomorrow. I focused
mainly on the markings on the die that indicated it was, in fact, a
Maxim chip but if there's any other region of the chip that you'd like
images of, please let me know and I'd be happy to take some more
pictures.
I hope you find this as interesting as I did.
Cheers!
-Pete
--
Pete Stephenson
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?
On Thu, Jul 27, 2017 at 12:31 PM, Pete Stephenson pete@heypete.com wrote:
Hi all,
A few days ago I reported the results from letting a DS3231 RTC run for
a year, and how the chip kept time well within the published specs.
Since I had acquired several DS3231s from dubious sources (Asian vendors
on a major auction site) as part of an RTC module that fits on the
Raspberry Pi's header pins, I was doubtful of the authenticity of the
chips. I decided to sacrifice one in the name of science and decapped it
at home using alternating heat (a lighter) and cold (a glass of cold
water) to embrittle the epoxy casing, then sanded down the back of the
chip on fine-grain sandpaper to expose what I hoped was the back of the
internals (so as not to damage the die itself).
Other than inadvertently sanding through half of the crystal's housing,
thus breaking one of the forks of the crystal, this was a success. (I
was prepared to decap one in acid had my attempt at physically removing
the epoxy package failed.) I slightly scratched the die itself while
separating it from the epoxy, but the die itself is clearly visible.
Based on a sample size of one and the markings on the die itself, it
appears the chip is authentic. The markings on the outside of the epoxy
package look a bit dubious and not like typical Maxim laser-markings, so
it's possible the chip was re-labeled at some point. I'll contact Maxim
to see if they can look up the lot information.
I used my 2 megapixel USB microscope to take some images throughout the
process that you might find interesting. The microscope has limited
resolution, particularly at high magnification, so some of the photos
may not be perfectly clear. I have access to a Zeiss petrographic
microscope at my work and will see if I can get some better images
tomorrow. I'll try to get high-quality images of the whole chip and
stitch them together into a larger composite.
Anyway, the photos are available at http://imgur.com/a/0zudj -- I will
add more photos from the petrographic microscope tomorrow. I focused
mainly on the markings on the die that indicated it was, in fact, a
Maxim chip but if there's any other region of the chip that you'd like
images of, please let me know and I'd be happy to take some more
pictures.
I hope you find this as interesting as I did.
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.
On Thu, Jul 27, 2017, at 09:31 PM, Pete Stephenson wrote:
[...]
Based on a sample size of one and the markings on the die itself, it
appears the chip is authentic. The markings on the outside of the epoxy
package look a bit dubious and not like typical Maxim laser-markings, so
it's possible the chip was re-labeled at some point. I'll contact Maxim
to see if they can look up the lot information.
[...]
Hi all,
Quick follow-up: I contacted Maxim to see if the chips were authentic,
and their very pleasant customer support people verified that the
markings and appearance of the chip are consistent with their records
for that year and lot number. That's a good thing.
They also reminded me that they only offer a warranty/guarantee on
products purchased either directly from them or from authorized
resellers. Asian auction-site vendors are not authorized resellers, so
please don't use products from such sources for Serious Business(tm).
Cheers!
-Pete
--
Pete Stephenson
Pete:
If you are concerned about someone copying a chip, you can not rely on the
original manufacturers' markings on the die.
I have experience where the counterfeiter just photocopied the chip layout,
including the original manufacturers marks, and copyright symbol and notice
from the original die.
So, when they copied the die, they really just copied it. Didn't change a
thing. It was not like they redesigned it, or were selling their own design
with equivalent functionality.
--- Graham / KE9H
==
On Thu, Jul 27, 2017 at 2:31 PM, Pete Stephenson pete@heypete.com wrote:
Hi all,
A few days ago I reported the results from letting a DS3231 RTC run for
a year, and how the chip kept time well within the published specs.
Since I had acquired several DS3231s from dubious sources (Asian vendors
on a major auction site) as part of an RTC module that fits on the
Raspberry Pi's header pins, I was doubtful of the authenticity of the
chips. I decided to sacrifice one in the name of science and decapped it
at home using alternating heat (a lighter) and cold (a glass of cold
water) to embrittle the epoxy casing, then sanded down the back of the
chip on fine-grain sandpaper to expose what I hoped was the back of the
internals (so as not to damage the die itself).
Other than inadvertently sanding through half of the crystal's housing,
thus breaking one of the forks of the crystal, this was a success. (I
was prepared to decap one in acid had my attempt at physically removing
the epoxy package failed.) I slightly scratched the die itself while
separating it from the epoxy, but the die itself is clearly visible.
Based on a sample size of one and the markings on the die itself, it
appears the chip is authentic. The markings on the outside of the epoxy
package look a bit dubious and not like typical Maxim laser-markings, so
it's possible the chip was re-labeled at some point. I'll contact Maxim
to see if they can look up the lot information.
I used my 2 megapixel USB microscope to take some images throughout the
process that you might find interesting. The microscope has limited
resolution, particularly at high magnification, so some of the photos
may not be perfectly clear. I have access to a Zeiss petrographic
microscope at my work and will see if I can get some better images
tomorrow. I'll try to get high-quality images of the whole chip and
stitch them together into a larger composite.
Anyway, the photos are available at http://imgur.com/a/0zudj -- I will
add more photos from the petrographic microscope tomorrow. I focused
mainly on the markings on the die that indicated it was, in fact, a
Maxim chip but if there's any other region of the chip that you'd like
images of, please let me know and I'd be happy to take some more
pictures.
I hope you find this as interesting as I did.
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.
Graham,
That's very true!
Still, my past experience with copied chips typically involves a
particular type of RS-232-to-TTL serial converter, the MAX3232. I've
found that nearly all of the ones from unauthorized distributors (e.g.
auction site vendors) are fake, even though the package is marked as
being MAX3232. After a few weeks the chips would fail in a way that
they'd pass high currents and get extremely hot.
I did a write-up on those chips at
https://blog.heypete.com/2016/09/11/investigating-fake-max3232-ttl-to-rs-232-chips/
and, after decapuslating them, discovered they were completely different
chips on the inside that were made to function the same way as the
MAX3232 (i.e., they converted RS-232 signals to TTL serial, operated on
the same voltages, had the same pinout, etc.).
In regards to the DS3231, I was concerned that the chip was also a fake
that functioned in the same way as the DS3231, presented the same
registers to the user, etc., but was actually a different design on the
inside. It appears that this is not the case, and in addition to
functioning as advertised, it also is legitimate. If it is a clone, it's
a goood one, but I don't think it is.
Cheers!
-Pete
--
Pete Stephenson
On Thu, Jul 27, 2017, at 10:34 PM, Graham / KE9H wrote:
Pete:
If you are concerned about someone copying a chip, you can not rely on
the
original manufacturers' markings on the die.
I have experience where the counterfeiter just photocopied the chip
layout,
including the original manufacturers marks, and copyright symbol and
notice
from the original die.
So, when they copied the die, they really just copied it. Didn't change a
thing. It was not like they redesigned it, or were selling their own
design
with equivalent functionality.
--- Graham / KE9H
==
On Thu, Jul 27, 2017 at 2:31 PM, Pete Stephenson pete@heypete.com
wrote:
Hi all,
A few days ago I reported the results from letting a DS3231 RTC run for
a year, and how the chip kept time well within the published specs.
Since I had acquired several DS3231s from dubious sources (Asian vendors
on a major auction site) as part of an RTC module that fits on the
Raspberry Pi's header pins, I was doubtful of the authenticity of the
chips. I decided to sacrifice one in the name of science and decapped it
at home using alternating heat (a lighter) and cold (a glass of cold
water) to embrittle the epoxy casing, then sanded down the back of the
chip on fine-grain sandpaper to expose what I hoped was the back of the
internals (so as not to damage the die itself).
Other than inadvertently sanding through half of the crystal's housing,
thus breaking one of the forks of the crystal, this was a success. (I
was prepared to decap one in acid had my attempt at physically removing
the epoxy package failed.) I slightly scratched the die itself while
separating it from the epoxy, but the die itself is clearly visible.
Based on a sample size of one and the markings on the die itself, it
appears the chip is authentic. The markings on the outside of the epoxy
package look a bit dubious and not like typical Maxim laser-markings, so
it's possible the chip was re-labeled at some point. I'll contact Maxim
to see if they can look up the lot information.
I used my 2 megapixel USB microscope to take some images throughout the
process that you might find interesting. The microscope has limited
resolution, particularly at high magnification, so some of the photos
may not be perfectly clear. I have access to a Zeiss petrographic
microscope at my work and will see if I can get some better images
tomorrow. I'll try to get high-quality images of the whole chip and
stitch them together into a larger composite.
Anyway, the photos are available at http://imgur.com/a/0zudj -- I will
add more photos from the petrographic microscope tomorrow. I focused
mainly on the markings on the die that indicated it was, in fact, a
Maxim chip but if there's any other region of the chip that you'd like
images of, please let me know and I'd be happy to take some more
pictures.
I hope you find this as interesting as I did.
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.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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and follow the instructions there.
Yes, I doubt that the volume on a specialty chip like the DS3231 is high
enough to attract the counterfeiters.
RS-232 chips and the FTDI USB to serial chips, and consumer FM tuner and
audio amplifier chips, is another story.
My experience was with a proprietary full custom IC that totally
implemented a 'pager' in a single IC package. The Chinese apparently wanted
to get into the the paging business, at the time. Of course, the
cellphones have now totally eaten the pager business, globally.
--- Graham
==
On Thu, Jul 27, 2017 at 8:21 PM, Pete Stephenson pete@heypete.com wrote:
Graham,
That's very true!
Still, my past experience with copied chips typically involves a
particular type of RS-232-to-TTL serial converter, the MAX3232. I've
found that nearly all of the ones from unauthorized distributors (e.g.
auction site vendors) are fake, even though the package is marked as
being MAX3232. After a few weeks the chips would fail in a way that
they'd pass high currents and get extremely hot.
I did a write-up on those chips at
<https://blog.heypete.com/2016/09/11/investigating-fake-
max3232-ttl-to-rs-232-chips/>
and, after decapuslating them, discovered they were completely different
chips on the inside that were made to function the same way as the
MAX3232 (i.e., they converted RS-232 signals to TTL serial, operated on
the same voltages, had the same pinout, etc.).
In regards to the DS3231, I was concerned that the chip was also a fake
that functioned in the same way as the DS3231, presented the same
registers to the user, etc., but was actually a different design on the
inside. It appears that this is not the case, and in addition to
functioning as advertised, it also is legitimate. If it is a clone, it's
a goood one, but I don't think it is.
Cheers!
-Pete
--
Pete Stephenson
On Thu, Jul 27, 2017, at 10:34 PM, Graham / KE9H wrote:
Pete:
If you are concerned about someone copying a chip, you can not rely on
the
original manufacturers' markings on the die.
I have experience where the counterfeiter just photocopied the chip
layout,
including the original manufacturers marks, and copyright symbol and
notice
from the original die.
So, when they copied the die, they really just copied it. Didn't change a
thing. It was not like they redesigned it, or were selling their own
design
with equivalent functionality.
--- Graham / KE9H
==
On Thu, Jul 27, 2017 at 2:31 PM, Pete Stephenson pete@heypete.com
wrote:
Hi all,
A few days ago I reported the results from letting a DS3231 RTC run for
a year, and how the chip kept time well within the published specs.
Since I had acquired several DS3231s from dubious sources (Asian
vendors
on a major auction site) as part of an RTC module that fits on the
Raspberry Pi's header pins, I was doubtful of the authenticity of the
chips. I decided to sacrifice one in the name of science and decapped
it
at home using alternating heat (a lighter) and cold (a glass of cold
water) to embrittle the epoxy casing, then sanded down the back of the
chip on fine-grain sandpaper to expose what I hoped was the back of the
internals (so as not to damage the die itself).
Other than inadvertently sanding through half of the crystal's housing,
thus breaking one of the forks of the crystal, this was a success. (I
was prepared to decap one in acid had my attempt at physically removing
the epoxy package failed.) I slightly scratched the die itself while
separating it from the epoxy, but the die itself is clearly visible.
Based on a sample size of one and the markings on the die itself, it
appears the chip is authentic. The markings on the outside of the epoxy
package look a bit dubious and not like typical Maxim laser-markings,
so
it's possible the chip was re-labeled at some point. I'll contact Maxim
to see if they can look up the lot information.
I used my 2 megapixel USB microscope to take some images throughout the
process that you might find interesting. The microscope has limited
resolution, particularly at high magnification, so some of the photos
may not be perfectly clear. I have access to a Zeiss petrographic
microscope at my work and will see if I can get some better images
tomorrow. I'll try to get high-quality images of the whole chip and
stitch them together into a larger composite.
Anyway, the photos are available at http://imgur.com/a/0zudj -- I will
add more photos from the petrographic microscope tomorrow. I focused
mainly on the markings on the die that indicated it was, in fact, a
Maxim chip but if there's any other region of the chip that you'd like
images of, please let me know and I'd be happy to take some more
pictures.
I hope you find this as interesting as I did.
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.
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.
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.
On Thu, Jul 27, 2017, at 09:31 PM, Pete Stephenson wrote:
[snip]
Anyway, the photos are available at http://imgur.com/a/0zudj -- I will
add more photos from the petrographic microscope tomorrow. I focused
mainly on the markings on the die that indicated it was, in fact, a
Maxim chip but if there's any other region of the chip that you'd like
images of, please let me know and I'd be happy to take some more
pictures.
Hi all,
Just a quick update: I was able to look at the DS3231 at work at the
quality of the (very expensive) Zeiss microscope is dramatically better
than my $20 USB microscope at home. No surprise.
Unfortunately, due to the ancient Canon camera attached to the
microscope not being compatible with Windows 7 or Linux, I was unable to
get any high-quality photos at this time. The camera is normally used in
tethered mode with no CF card, with the camera connected to the user's
laptop. Most of my colleagues use Macs, which evidently do work with it
but I wasn't able to ask any of them today before they all left. I've
ordered a CF-to-SD adapter that should allow me to take photos without
any issues, but it will be a few weeks until it arrives. Once it's
arrived, I'll take some more photos of the chip and let people know.
I've taken a few photos with my smartphone through the microscope's
eyepiece, but they turned out quite poorly as you can see below. When
viewed directly via the eyepiece, the appearance of the chip is quite
stunning.
On a related note, the reflected differential interference contrast
(DIC) filters on the microscope make looking at multi-layer chips
dramatically more clear and interesting. Compare
http://imgur.com/7nuTooL , which was taken with with no optical
filtering using standard reflected light illumination and
http://imgur.com/P6HL9MB which was taken of a different area of the chip
using reflected DIC. The colors are different, of course, but the
contrast between elements of the chip is much improved.
If anyone has any chips they'd like me to examine under the microscope,
let me know and I'd be happy to do so.
Cheers!
-Pete
--
Pete Stephenson
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
On Sat, 29 Jul 2017 20:32:30 +0200
Pete Stephenson pete@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
On Sun, Jul 30, 2017, at 11:15 AM, Attila Kinali wrote:
On Sat, 29 Jul 2017 20:32:30 +0200
Pete Stephenson pete@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
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
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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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