1 Introduction

The Bluetooth specification puts a strict requirement on the accuracy of the sleep clocks for Bluetooth Low Energy devices that are intended to enter (and stay) in a connection. The specification requires that devices have a sleep clock accuracy (SCA) that meets ± 500 ppm. For more details on the SCA requirement, see the Sleep Clock Accuracy section in the Bluetooth core specification 4.0, Volume 6. that can be downloaded from the following URL: https://www.bluetooth.com/specifications/adopted-specifications.

This sleep clock accuracy (SCA) requirement is valid for both the master and slave side of the Bluetooth Low Energy connection; however, devices such as Bluetoooth Low Energy beacons do not require such accuracy as the advertising interval is intentionally varied to prevent collisions. The intention of the SCA requirement is to ensure low power consumption while maintaining flexibility in the component selection. The amount of time a slave device must stay in active RX mode, referred to as the receive window, is dependent upon the sleep clock tolerance; a less accurate sleep clock requires the receive window time to be increased, thus, increasing the average current consumption.