BCM43907 Preliminary Data Sheet
External Frequency Reference
External Frequency Reference
As an alternative to a crystal, an external precision frequency reference can be used, provided that it meets the
phase noise requirements listed in Table 3.
If used, the external clock should be connected to the WRF_XTAL_XON 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 BCM43907 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_VDD1P35 pin.
Figure 6: Recommended Circuit to Use With an External Reference Clock
1000 pF
Reference
WRF_XTAL_XON
Clock
NC
WRF_XTAL_XOP
Table 3: Crystal Oscillator and External Clock—Requirements and Performance
External Frequency
Crystala
Referenceb c
Parameter
Conditions/Notes
Min. Typ. Max. Min. Typ. Max. Units
d
Frequency
2.4 GHz band:
IEEE 802.11n operation and
legacy IEEE 802.11b/g operation
Between 19 MHz and 52 MHz
5 GHz band,
IEEE 802.11n operation only
19
–
–
52
20
35
–
–
52
20
MHz
ppm
Frequencytolerance Without trimming
over the lifetime of
the equipment,
–20
–20
including
e
temperature
Crystal load
capacitance
–
–
–
–
16
–
–
–
–
pF
ESR
–
–
60
–
–
–
–
–
–
–
Ω
Drive level
External crystal must be able to 200
tolerate this drive level.
µW
Input impedance
(WRF_XTAL_XON)
Resistive
–
–
–
–
–
–
–
30k
–
100k
–
Ω
Capacitive
7.5
–
–
–
7.5
0.2
pF
V
WRF_XTAL_XON DC-coupled digital signal
Input low level
0
WRF_XTAL_XON DC-coupled digital signal
Input high level
–
–
–
1.0
–
1.26
V
Broadcom®
March 12, 2016 • 43907-DS104-R
Page 25
BROADCOM CONFIDENTIAL
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