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Topic: Using a Oscillator vs. Crystal with Caps (Read 380 times) previous topic - next topic

Constantin

Hi, I wonder if anyone can enlighten me regarding the relative merit of using a crystal with load capacitors vs. an actively-driven oscillator like this Abracon. Is this a pure cost decision?

I really appreciated the ease with which some resonators could be used with Atmegas and wonder if oscillators like the one above (plus a de-coupling capacitor) might also make my life easier (in return for a small additional cost and a VDD line to the oscillator). Thoughts?

Erdin

If the price would be almost the same, the clock oscillators would be used.
However, a crystal with two capacitor is easy.
If an Arduino enters sleep mode, a crystal uses no power.
The avr chips can use a crystal or a resonator. Some Arduino boards use a resonator.

CrossRoads

Oscillator is nice as you can get one that is thermally compesated &  higher accuracy, good for clock applications.'

As you can see from this selection of MEMS oscillators from Digikey, they are kind of pricey look at 1-lots:
http://www.digikey.com/scripts/dksearch/dksus.dll?pv183=3135&FV=fff4000d%2Cfff8016e%2C22c0011&k=oscillator&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
Stability is quoted at +/- 10ppm.  3.3V power is needed.
It draws quite a bit of current while operating - 7mA typical.
It requires a load resistor of at least 10K.
It has a slow start up time- 1.5mS typical = 24000 clock cycles.

Crystals are much less, and are available with same +/- 10ppm
http://www.digikey.com/scripts/dksearch/dksus.dll?pv139=17&pv253=19&pv537=1&FV=fff4000d%2Cfff8016d&k=crystal&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
3.3v power is not needed, oscillation is powered by '328P buffers.
No external load resistor is required.
The '328P has programmable # of clock cyckes to start, see seciton 9 of the datasheet:
"The oscillator is required to oscillate for a minimum number of cycles before the clock is considered stable. An
internal ripple counter monitors the oscillator output clock, and keeps the internal reset active for a given number of
clock cycles. The reset is then released and the device will start to execute. The recommended oscillator start-up
time is dependent on the clock type, and varies from 6 cycles for an externally applied clock to 32K cycles for a low
frequency crystal."
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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