AN95089 - PSoC® 4/PRoC™ BLE Crystal Oscillator Selection and Tuning Techniques

AN95089 guides you in selecting the external crystal oscillator (ECO) and watch crystal oscillator (WCO) for PSoC 4/ PRoC BLE devices to achieve good RF performance. The AN gives insights into crystal basics and clock accuracy measurements. Cypress-recommended crystals and tuning techniques for optimum performance are also discussed.

Introduction

This application note helps you select the crystal for the ECO and WCO for PSoC 4/PRoC BLE devices and tune them for optimum performance. The on-chip ECO circuit with an external crystal is used to derive a 24-MHz clock to run the BLE subsystem. This clock is used to determine the protocol timing for link-layer operations and to derive 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. Bluetooth Low Energy (BLE) is a timing-sensitive technology in which an inaccurate ECO clock can degrade the RF performance at the physical layer; similarly, an inaccurate WCO clock can lead to increased power consumption in a peripheral.