AN95089 Datasheet, PDF (15/19 Pages) Ramtron International Corporation – BLE Crystal Oscillator Selection and Tuning Techniques

PSoC® 4/PRoC™ BLE Crystal Oscillator Selection and Tuning Techniques
7 Route PCB traces symmetrically to have the same parasitic capacitance on both crystal pins.
Figure 13 illustrates the above points more clearly. Some of the layout considerations are highlighted in this
figure.
Figure 13. PCB layout with Crystals
11 Summary
 The BLE protocol requires that the ECO crystal clock accuracy is within ± 50 ppm.
 An inaccurate ECO crystal frequency results in poor RF performance.
 An inaccurate WCO crystal frequency results in high current consumption.
 The ECO crystal frequency inaccuracy can be corrected by following the 5-step process.
 Tuning is not required for every board and need to be done only once during development.
 A 2:1 ratio for the two external capacitors for the WCO crystal is required for optimal power consumption and
performance.
 Temperature, aging, and parasitic capacitance cause variations in the crystal clock accuracy.
 The crystal should be positioned close to the chip to minimize parasitic capacitances.
12 References
The following references provide further detailed information
Oscillator Concepts
 http://www.abracon.com/Support/facn_abracon_jul2011.pdf
 http://www.electronics-tutorials.ws/oscillator/crystal.html
 http://kunz-pc.sce.carleton.ca/thesis/CrystalOscillators.pdf
 http://services.eng.uts.edu.au/pmcl/de/Downloads/Lecture04.pdf
 http://www.am1.us/Local_Papers/U11625%20VIG-TUTORIAL.pdf
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Document No. 001-95089 Rev. *A
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