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Topic: Using a Oscillator vs. Crystal with Caps (Read 450 times) previous topic - next topic


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?


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.


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:
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
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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