BCM43907 Preliminary Data Sheet
Frequency References
Section 3: Frequency References
An external crystal is used for generating all radio frequencies and normal-operation clocking. As an alternative,
an external frequency reference can be used. In addition, a low-power oscillator (LPO) is provided for lower
power mode timing.
Crystal Interface and Clock Generation
The BCM43907 can use an external crystal to provide a frequency reference. The recommended crystal
oscillator configuration, including all external components, is shown in Figure 5. Consult the reference
schematics for the latest configuration.
Figure 5: Recommended Oscillator Configuration
Device boundary
C
WRF_XTAL_XON
1.3 pF
27 pF
Programmable internal shunt caps are
from 0 pF to 7.5 pF in steps of 0.5 pF.
37.4 MHz
C
WRF_XTAL_XOP
x ohms
0.4 pF
27 pF
External resistor and programmable
internal resistor value is determined
by crystal drive level.
Programmable internal series resistor is from 50 ohms to 500 ohms
in steps of 50 ohms. Boot-up ROM value is 50 ohms.
Note: A reference schematic is available for further details. Contact your Broadcom FAE.
A fractional-N synthesizer in the BCM43907 generates the radio frequencies, clocks, and data/packet timing,
enabling it to operate using a wide selection of frequency references.
The recommended default frequency reference is a 37.4 MHz crystal. The signal characteristics for the crystal
interface are listed in Table 3 on page 25.
Note: Although the fractional-N synthesizer can support alternative reference frequencies,
frequencies other than the default require support to be added in the driver, plus additional extensive
system testing. Contact Broadcom for further details.
Broadcom®
March 12, 2016 • 43907-DS104-R
Page 24
BROADCOM CONFIDENTIAL
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