Choosing the correct crystal oscillator for best wireless device performance (part 2)

摘要

The first part of this technical briefing (see Ultra Low Power Wireless Quarter Q1 2009) described how the accuracy of the crystal reference is the only factor determining the accuracy of the RF device. Here we consider how errors in loading can have a significant effect on that accuracy. Figure 3 shows a schematic of a typical crystal circuit diagram. The crystal (XI) is loaded with capacitors (Cl and C2) and the resistor (Rl) provides bias for the crystal oscillator located inside the nRF24xxx transceiver. The value of Rl is not critical and is usually set to a large value, for example, 1MΩ.