BCM4325
Preliminary Data Sheet
6/30/09
Section 3: Frequency References
The BCM4325 uses the following external frequency references for normal and low-power operational modes:
•
An external crystal or external frequency reference driven by a temperature-compensated crystal oscillator (TCXO)
signal for generating all radio frequencies and normal operation clocking.
•
An external 32.768-kHz Low Power Oscillator (LPO) for low-power mode timing.
CRYSTAL INTERFACE AND CLOCK GENERATION
The BCM4325 uses a fractional-N synthesizer to generate the radio frequencies, clocks, and data/packet timing that enables
it to operate using a wide range of frequency references. An external source, such as a TCXO or a crystal interfaced directly
to the BCM4325, can be used. The default frequency reference setting is a 26 MHz crystal or TCXO. Table 2 list the
requirements and characteristics for the crystal or frequency reference.
Table 2: Crystal Interface Signal Characteristics
Parameter
Crystal
External Freq. Reference
Units
Frequency range
12–52 MHz in 2 ppm stepsd
12–52 MHz, in 2-ppm steps b
–
Crystal load capacitance
ESR (maximum)
12 e
N/A
pF
Ω
60
–
Power dissipation, max
Input signal AC amplitude
Signal type
200
N/A
N/A
N/A
–
uW
mVp-p
–
400 to 1200 f
Square wave or sine wave
Input impedance
≥ 1
≤ 4.7
MΩ
pF
Phase noise (maximum for f = 26 MHz a)
1 kHz
–
–
–
–
≤ –100
≤ –115
≤ –120
≤ –140
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
10 kHz
100 kHz
1 MHz
Auto-detection frequencies when using LPO b, c 12, 13, 14.4, 15.36, 16.2, 16.8, 12, 13, 14.4, 15.36, 16.2, 16.8, MHz
18, 19.2, 19.44, 19.68, 19.8,
20, 24, 26, 38.4
18, 19.2, 19.44, 19.68, 19.8,
20, 24, 26, 38.4
Frequency tolerance plus over temperature
without trimming
20
20
ppm
Initial frequency tolerance trimming range
50
50
ppm
ms
Time for stable system clock after power up or
XTAL_PU assertion
Warm-up time < 6 ms
Maximum hold time for host
< 6 ms
a. For a clock reference other than 26 MHz, 20*log10(f/26) dB should be added to the limits, where f = the reference clock
frequency in MHz.
b. Auto-detection of frequencies requires that the crystal or external frequency reference have less than 50 ppm of variation,
and the external LPO frequency have less than 200 ppm of variation at the time of auto-detection.
c. 52 MHz frequency reference is also supported. The BT_TM6 signal should be pulled low for 52 MHz clock reference.
d. The frequency step size is approximately 80 Hz resolution.
e. The precise value of load capacitance to center the frequency tolerance is dependent on board layout; see Broadcom
reference schematics for exact values.
Broadcom Corporation
Page 6
Frequency References
Document 4325-DS04-R
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