BCM20705 Datasheet, PDF (36/67 Pages) Cypress Semiconductor – Single-Chip Bluetooth Transceiver and Baseband Processor

BCM20705 Data Sheet
Frequency References
Section 6: Frequency References
The BCM20705 uses two different frequency references for normal and low-power operational modes. An
external crystal or frequency reference driven by a Temperature Compensated Crystal Oscillator (TCXO) signal
is used to generate the radio frequencies and normal operation clocking. Either an external 32.768 kHz or fully
integrated internal Low-Power Oscillator (LPO) is used for low-power mode timing.
Crystal Interface and Clock Generation
The BCM20705 uses a fractional-N synthesizer to generate the radio frequencies, clocks, and data/packet
timing, enabling it to operate from any of a multitude of frequency sources. The source can be external, such as
a TCXO, or a crystal interfaced directly to the device.
The default frequency reference setting is for a 20 MHz crystal or TCXO. The signal characteristics for the
crystal interface are listed in Table 4 on page 35.
Table 4: Crystal Interface Signal Characteristics
Parameter
Crystal
External Frequency Reference Units
Acceptable frequencies
12–52 MHz in 2 ppm^a steps 12–52 MHz in 2 ppm^a steps
–
Crystal load capacitance
12 (typical)
N/A
pF
ESR
60 (max)
–
Ω
Power dissipation
200 (max)
–
μW
Input signal amplitude
N/A
400 to 2000
mVp-p
2000 to 3300 (requires a 10 pF
DC blocking capacitor to
attenuate the signal)
Signal type
N/A
Square-wave or sine-wave
–
Input impedance
N/A
≥1
MΩ
≤2
pF
Phase noise
@ 1 kHz
@ 10 kHz
@ 100 kHz
@ 1 MHz
N/A
–
–
N/A
< –120^b
dBc/Hz
N/A
< –131^b
dBc/Hz
N/A
< –136^b
dBc/Hz
N/A
< –136^b
dBc/Hz
Auto-detection frequencies when
using external LPO^c
12, 13, 14.4, 15.36, 16.2, 12, 13, 14.4, 15.36, 16.2, 16.8, MHz
16.8, 18, 19.2, 19.44, 19.68, 18, 19.2, 19.44, 19.68, 19.8, 20,
19.8, 20, 24, 26, 33.6, 37.4, 24, 26, 33.6, 37.4, and 38.4
and 38.4
Tolerance without frequency trimming^d ±20
±20
ppm
Initial frequency tolerance trimming ±50
±50
ppm
range
a. The frequency step size is approximately 80 Hz resolution.
Broadcom®
Bluetooth Transceiver and Baseband Processor
November 13, 2014 • MCS20705-DS104-R
Page 35
BROADCOM CONFIDENTIAL