AN95089 Datasheet, PDF (1/19 Pages) Ramtron International Corporation – BLE Crystal Oscillator Selection and Tuning Techniques

AN95089
PSoC^® 4/PRoC™ BLE Crystal Oscillator Selection and Tuning Techniques
Author: Prakhar Agarwal
Associated Part Family: CY8C4XX7-BL, CY8C4xx8-BL, CYBL10X6X, CYBL10x7x
Related Application Notes: None
AN95089 provides insights into the selection and tuning of the external crystal oscillator (ECO) and watch crystal oscillator
(WCO) for PSoC 4/ PRoC BLE devices to achieve a good RF performance. This application note introduces basics of
crystals and clock accuracy measurements. Cypress-recommended crystals and tuning techniques for optimum
performance are also discussed.
Contents
1 Introduction...............................................................1
2 Crystal Oscillator Basics...........................................2
2.1 Crystal Oscillator Circuitry................................2
2.2 Load Cap Value (CL)........................................2
2.3 Crystal Equivalent RLC Circuit.........................4
2.4 Drive Level.......................................................5
2.5 PPM Error ........................................................5
3 Effects of Inaccurate ECO Crystal Frequency
on RF Performance ..................................................5
4 Crystal Tuning Technique for ECO...........................6
4.1 Steps to Correct Clock Inaccuracy...................7
5 Is Tuning Required for Each Board? ........................8
6 Crystal Analysis for ECO ........................................10
6.1 Frequency Variation with Temperature ..........10
6.2 Frequency Variation with Load Cap Value.....10
7 Recommendation for ECO ..................................... 11
8 Crystal Analysis for WCO .......................................11
8.1 Frequency Variation with Temperature..........11
8.2 Start-Up Time and ESR ................................. 12
8.3 Load Capacitance..........................................12
8.4 CL and Clock Accuracy ................................. 13
8.5 Frequency Variation Across Boards .............. 13
9 Recommendations for WCO...................................14
10 Layout Considerations for PCB .............................. 14
11 Summary ................................................................ 15
12 References ............................................................. 15
13 Appendix: Frequency Error
(Transmit Center Frequency Tolerance) ................ 17
Worldwide Sales and Design Support.............................19
1 Introduction
This application note helps you select the ECO crystal and the WCO crystal for PSoC 4/PRoC BLE devices and tune
them for optimum performance.
Bluetooth Low Energy (BLE) is a timing-sensitive technology in which an inaccurate ECO clock can degrade the
physical layer RF performance; similarly, an inaccurate WCO clock can lead to increased power consumption in a
peripheral.
The on-chip ECO circuit with an external crystal is used to synthesize a 24-MHz clock to run the BLE subsystem. The
clock sets the protocol timing for link-layer operations and derives the carrier frequency for physical-layer RF circuits.
An external WCO crystal is used to derive the 32.768-kHz clock that maintains link-layer timing synchronization when
the BLE subsystem is in a low-power mode.
www.cypress.com
Document No. 001-95089 Rev. *A
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