D.A.(Tony)Stewart
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I started R&D right after graduation in 1975 and discovered Crystal Oscillators (XO) had already been around for a long time and since CMOS came out, the best way back then for a 10~20MHz XO is still used today because of its low, cost, high quality square wave and low power for PIC's and ATMEGA's etc. The configuration is called Pierce Oscillator design and requires a simple CMOS inverting gate. Using a parallel high impedance resonance with negative signal feedback guarantees the criteria for oscillation discovered in 1921.
Every Crystal has a series LC resonance and a parallel LC resonance slightly offset and the actual cut of the crystal could be Either tuned for Series or Parallel with any load Capacitance up to 50pF ( already noted 15~20 pF is most common)
There are endless variations and complexities, improvements and reasons for every choice, which I won't get into. But if you decide you want to learn a little more about different crystal oscillator configurations , here is a primer using transistors. The Colpitts is still used today in the GHz range with MOSFETs and special MEMS designs, but many use a PLL to multiply the clock.
The acronyms for XO's are based on X as the abbreviation or Reference Designation in Schematics for crystals.
See if you can guess the abbreviations.... XO, VCXO, TCXO, OCXO, DT-TCXO, etc etc.
Normally the Cap. used is 2x the rated load pF and split into 2 equal caps to end up with rated load. But there are technical reasons for differences, such as for wider tuning range for example. But if you use in the Series Mode, you may find the frequency off by a few hundred ppm.
There are entire books on this simple easy to use part. and a wealth of knowledge and experience in this forum.
Every Crystal has a series LC resonance and a parallel LC resonance slightly offset and the actual cut of the crystal could be Either tuned for Series or Parallel with any load Capacitance up to 50pF ( already noted 15~20 pF is most common)
There are endless variations and complexities, improvements and reasons for every choice, which I won't get into. But if you decide you want to learn a little more about different crystal oscillator configurations , here is a primer using transistors. The Colpitts is still used today in the GHz range with MOSFETs and special MEMS designs, but many use a PLL to multiply the clock.
The acronyms for XO's are based on X as the abbreviation or Reference Designation in Schematics for crystals.
See if you can guess the abbreviations.... XO, VCXO, TCXO, OCXO, DT-TCXO, etc etc.
Normally the Cap. used is 2x the rated load pF and split into 2 equal caps to end up with rated load. But there are technical reasons for differences, such as for wider tuning range for example. But if you use in the Series Mode, you may find the frequency off by a few hundred ppm.
There are entire books on this simple easy to use part. and a wealth of knowledge and experience in this forum.