BCM4330 Preliminary Data Sheet
TCXO
TCXO
As an alternative to a crystal, an external precision TCXO can be used as the frequency reference, provided that
it meets the Phase Noise requirements listed in Table 2. When the clock is provided by an external TCXO, there
are two possible connection methods, as shown in Figure 6 and Figure 7:
1. If the TCXO is dedicated to driving the BCM4330, it should be connected to the WRF_XTAL_OP pin through
an external 1000 pF coupling capacitor, as shown in Figure 6. The internal clock buffer connected to this pin
will be turned OFF when the BCM4330 goes into sleep mode. When the clock buffer turns ON and OFF
there will be a small impedance variation. Power must be supplied to the WRF_XTAL_VDD1P2 pin.
2. For 2.4 GHz operation only, an alternative is to DC-couple the TCXO to the WRF_TCXO_IN pin, as shown in
Figure 7. Use this method when the same TCXO is shared with other devices and a change in the input
impedance is not acceptable because it may cause a frequency shift that cannot be tolerated by the other
device sharing the TCXO. This pin is connected to a clock buffer powered from WRF_TCXO_VDD. If the
power supply to this buffer is always on (even in sleep mode), the clock buffer is always on, thereby
ensuring a constant input impedance in all states of the device. The maximum current drawn from
WRF_TCXO_VDD is approximately 500 µA.
1000 pF
TCXO
WRF_XTAL_OP
WRF_XTAL_ON
WRF_TCXO_IN
NC
WRF_TCXO_VDD3P3
Figure 6: Recommended Circuit to Use with an External Dedicated TCXO
To other devices
TCXO
WRF_TCXO_IN
WRF_TCXO_VDD
WRF_XTAL_OP
To always present 1.7V to 3.3V supply
WRF_XTAL_ON
NC
Figure 7: Recommended Circuit to Use with an External Shared TCXO
®
BROADCOM
BCM4330 Preliminary Data Sheet
April 28, 2011 • 4330-DS304-RI
Page 33
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