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Crystal Oscillator

BCM20705 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

Bluetooth Transceiver and Baseband Processor

November 13, 2014 • MCS20705-DS104-R

Page 37

Crystal Oscillator

The BCM20705 can use an external crystal to provide a frequency reference. The recommended configuration

for the crystal oscillator, including all external components, is shown in Figure 7.

Figure 7: Recommended Oscillator Configuration

External Frequency Reference

An external frequency reference, such as VDD_RF, collectively refers to several RF power supplies generated

by a TCXO signal that may be directly connected to the crystal input pin on the BCM20705, as shown in

Figure 8. The external frequency reference input is designed to not change loading on the TCXO when the

BCM20705 is powered up or powered down.

When using the BCM20705 with the TXCO OR gate option, GPIO 6 must be driven active high or active low.

Excessive leakage current results if GPIO6 is allowed to float.

Figure 8: Recommended TCXO Connection

0 ~18 pF*

XIN

XOUT

Crystal

Oscillator

*Capacitor value range depends

on the manufacturer of the XTAL

as well as board layout.

No Connection

TCXO

XIN

XOUT

10–1000 pF*

* Recommended value is 100 pF.

Higher values produce a longer startup time.

Lower values have greater isolation.

Larger values help small signal swings.

BCM20705 Datasheet(PDF) 38 Page - Cypress Semiconductor