Accurate Internal Oscilator

Hello,

For many years we are using pic 8 bit micros for our product. We have come
to a point we are considering a new solution. The pic internal oscilator is
not accurate enough for our application because it is based on RC
technology.
We need an internal oscillator because we are becoming very tight in
phisical space(volume wise).

My Question is. can someone point 8bit mcu with Acuurate Intenal
Oscillator- less then 50ppm tolerance)

Thanks,

Roy Azriel 

royazriel wrote:

> For many years we are using pic 8 bit micros for our product. We have come
> to a point we are considering a new solution. The pic internal oscilator is
> not accurate enough for our application because it is based on RC
> technology.
> We need an internal oscillator because we are becoming very tight in
> phisical space(volume wise).
> 
> My Question is. can someone point 8bit mcu with Acuurate Intenal
> Oscillator- less then 50ppm tolerance)

I've never seen anything that accurate for an internal oscillator.

Have you considered a miniature external crystal ? For example:

http://www.ecsxtal.com/store/pdf/ecx-2236.pdf

On Feb 9, 9:47 am, Arlet Ottens <usene...@c-scape.nl> wrote:
> royazriel wrote:
> > For many years we are using pic 8 bit micros for our product. We have come
> > to a point we are considering a new solution. The pic internal oscilator is
> > not accurate enough for our application because it is based on RC
> > technology.
> > We need an internal oscillator because we are becoming very tight in
> > phisical space(volume wise).

We are pondering the same issue for an AVR.  Will a watch crystal
(32KHz) work for you?  We are considering mounting it on top of the
AVR with a custom lead frame.

>
> > My Question is. can someone point 8bit mcu with Acuurate Intenal
> > Oscillator- less then 50ppm tolerance)
>
> I've never seen anything that accurate for an internal oscillator.
>
> Have you considered a miniature external crystal ? For example:
>
> http://www.ecsxtal.com/store/pdf/ecx-2236.pdf

They are very expensive, of the order of $1 each vs. 10 to 20 cents
for regular crystal.

On Feb 9, 12:18=A0pm, "royazriel" <ro...@zahav.net.il> wrote:

> My Question is. can someone point 8bit mcu with Acuurate Intenal
> Oscillator- less then 50ppm tolerance)

Take a close look at the MSP430F20xx series, specifically 2001/2011,
2002/2012, 2003/2013. The internal oscillator is factory calibrated
and surprisingly good over temperature and voltage. But the parts are
very small.

The next best thing I'd suggest is any of the other MSP430 family,
with a 32.768kHz crystal of the required accuracy, and use the
internal DCO calibrated against the 32k crystal.

royazriel wrote:

> For many years we are using pic 8 bit micros for our product. We have come
> to a point we are considering a new solution. The pic internal oscilator is
> not accurate enough for our application because it is based on RC
> technology.
> We need an internal oscillator because we are becoming very tight in
> phisical space(volume wise).
> 
> My Question is. can someone point 8bit mcu with Acuurate Intenal
> Oscillator- less then 50ppm tolerance)

The 50ppm tolerance requires a crystal or ceramic resonator. Among the 
other suggested solutions, you can use the AC power frequency as a 
reference. A microcontroller like MSP430 or HC908 can use the PLL to 
lock on the AC frequency directly. With the other microcontrollers, you 
may be able to correct either the internal oscillator itself or the 
critical frequencies derived from the oscillator by using the AC as the 
ref. clock.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Arlet Ottens wrote:
> royazriel wrote:
> 
>> For many years we are using pic 8 bit micros for our product. We have 
>> come
>> to a point we are considering a new solution. The pic internal 
>> oscilator is
>> not accurate enough for our application because it is based on RC
>> technology.
>> We need an internal oscillator because we are becoming very tight in
>> phisical space(volume wise).
>>
>> My Question is. can someone point 8bit mcu with Acuurate Intenal
>> Oscillator- less then 50ppm tolerance)

Over what temperature and voltage range ?
Does this have any field-signals for Cal-Check, or do you also
want this stable over the product life too ?

> 
> 
> I've never seen anything that accurate for an internal oscillator.
> 
> Have you considered a miniature external crystal ? For example:
> 
> http://www.ecsxtal.com/store/pdf/ecx-2236.pdf

No one makes that precision, which is one part in 20,000.
Trimmed RC osc are in the one part in 100 range, with trims steps to
around one part in 250 - so the OP is chasing around 100x the
start of the art.

  Single package precisions like this, may be possible in years to come, 
with the Silicon MEMS oscillators.
  This is likely to be Dual-Die solutions, but with a custom Osc that
matches the needs of the MEMS block. See SiTime's web site - their
special bridge is 0.8mm x 0.6mm x 0.15mm, so can fit into a
molded package.

-jg

On Feb 9, 8:47 pm, Jim Granville <no.s...@designtools.maps.co.nz>
wrote:
> Arlet Ottens wrote:
> > royazriel wrote:
>
> >> For many years we are using pic 8 bit micros for our product. We have
> >> come
> >> to a point we are considering a new solution. The pic internal
> >> oscilator is
> >> not accurate enough for our application because it is based on RC
> >> technology.
> >> We need an internal oscillator because we are becoming very tight in
> >> phisical space(volume wise).
>
> >> My Question is. can someone point 8bit mcu with Acuurate Intenal
> >> Oscillator- less then 50ppm tolerance)
>
> Over what temperature and voltage range ?
> Does this have any field-signals for Cal-Check, or do you also
> want this stable over the product life too ?
>
>
>
> > I've never seen anything that accurate for an internal oscillator.
>
> > Have you considered a miniature external crystal ? For example:
>
> >http://www.ecsxtal.com/store/pdf/ecx-2236.pdf
>
> No one makes that precision, which is one part in 20,000.
> Trimmed RC osc are in the one part in 100 range, with trims steps to
> around one part in 250 - so the OP is chasing around 100x the
> start of the art.
>
>   Single package precisions like this, may be possible in years to come,
> with the Silicon MEMS oscillators.
>   This is likely to be Dual-Die solutions, but with a custom Osc that
> matches the needs of the MEMS block. See SiTime's web site - their
> special bridge is 0.8mm x 0.6mm x 0.15mm, so can fit into a
> molded package.

This might work for us.  We will have three to four die on a hybrid
anyway.  We will likely buy a life-time (project or my life, whichever
come first) supply of AVR169 die to pack with it.

On Sat, 09 Feb 2008 18:35:57 -0600, Vladimir Vassilevsky
<antispam_bogus@hotmail.com> wrote:

>The 50ppm tolerance requires a crystal or ceramic resonator. Among the 
>other suggested solutions, you can use the AC power frequency as a 
>reference. A microcontroller like MSP430 or HC908 can use the PLL to 
>lock on the AC frequency directly. With the other microcontrollers, you 
>may be able to correct either the internal oscillator itself or the 
>critical frequencies derived from the oscillator by using the AC as the 
>ref. clock.

While the AC mains have a very good long time accuracy in most
countries, since the generators are driven at a small overspeed at
night to catch up any cycles lost during high demand during the day, a
mains driven clock can be off by several seconds during the day
(frequency error up to 100 ppm or even more). Last time I looked at
http://www.fingrid.fi/portal/in_english/electricity_market/state_of_power_system/
the Finnish (and hence also Nordic network) frequency was 49.97 Hz and
the time error more than 23 s.

This may be an issue if the time is compared to an accurate time
source (NTP, GPS etc.) e.g. one system running of the mains and the
other from some NTP source. 

However, if it is just needed that two (or more) devices keep the same
time, regardless of accuracy, the AC mains is a good clock source,
however, there may be a 7-15 ms time offset, if the devices are
powered from different phases in a 3-phase distribution system.

Some precaution is also needed to avoid false clock pulses due to all
kind of interference riding on the AC mains voltage. For devices
intended to work all over the world, some logic is needed to sense if
50 or 60 Hz mains is used.

Paul
 

On Sat, 09 Feb 2008 11:18:57 -0600, the renowned "royazriel"
<royaz@zahav.net.il> wrote:

>Hello,
>
>For many years we are using pic 8 bit micros for our product. We have come
>to a point we are considering a new solution. The pic internal oscilator is
>not accurate enough for our application because it is based on RC
>technology.
>We need an internal oscillator because we are becoming very tight in
>phisical space(volume wise).
>
>My Question is. can someone point 8bit mcu with Acuurate Intenal
>Oscillator- less then 50ppm tolerance)
>
>Thanks,
>
>Roy Azriel 

The only practical way to get 50ppm absolute frequency tolerance over
temperature is with a crystal or an external oscillator that uses a
crystal. With the latter you'll get a guarantee, but it tends to use
more power. If absolute tolerance isn't important (say 5000ppm) and 15
or 25ppm/K typical tempco is okay then consider a small SMT ceramic
resonator. 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

> > With the other microcontrollers, you
> >may be able to correct either the internal oscillator itself or the
> >critical frequencies derived from the oscillator by using the AC as the
> >ref. clock.
>
> While the AC mains have a very good long time accuracy in most
> countries, since the generators are driven at a small overspeed at
> night to catch up any cycles lost during high demand during the day, a
> mains driven clock can be off by several seconds during the day
> (frequency error up to 100 ppm or even more).

The uC can adjust for this error if necessary, since it needs to
sample the frequency anyway.  Perhaps you can also adjust it with a
light sensor.

However, when space is the constraint, AC is usually not available.
This is true in my case and probably true in the OP's case as well.