PRELIMINARY
CYW20710
6. Frequency References
The CYW20710 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.
6.1 Crystal Interface and Clock Generation
The CYW20710 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.
Table 4. Crystal Interface Signal Characteristics
Parameter
Acceptable frequencies
Crystal
External Frequency Reference
Units
12–52 MHz in 2 ppm1 steps
12–52 MHz in 2 ppm1 steps
–
Crystal load capacitance
ESR
12 (typical)
60 (max)
200 (max)
N/A
N/A
pF
Ω
–
Power dissipation
Input signal amplitude
–
μW
400 to 2000
mVp-p
2000 to 3300 (requires a 10 pF DC
blocking capacitor to attenuate the
signal)
Signal type
N/A
N/A
Square-wave or sine-wave
–
Input impedance
1
2
MΩ
pF
Phase noise
@ 1 kHz
@ 10 kHz
@ 100 kHz
@ 1 MHz
N/A
N/A
N/A
N/A
N/A
–
–
< –1202
< –1312
< –1362
< –1362
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
Auto-detection frequencies when using
external LPO3
12, 13, 14.4, 15.36, 16.2, 16.8, 12, 13, 14.4, 15.36, 16.2, 16.8, 18,
18, 19.2, 19.44, 19.68, 19.8, 20, 19.2, 19.44, 19.68, 19.8, 20, 24, 26,
MHz
24, 26, 33.6, 37.4, and 38.4
33.6, 37.4, and 38.4
Tolerance without frequency trimming4
±20
±20
±50
ppm
ppm
Initial frequency tolerance trimming range ±50
1. The frequency step size is approximately 80 Hz resolution.
2. With a 26 MHz reference clock. For a 13 MHz clock, subtract 6 dB. For a 52 MHz clock, add 6 dB.
3. Auto-detection of the frequency requires the crystal or external frequency reference to have less than ±50 ppm of variation and also requires
an external LPO frequency which has less than ±250 ppm of variation at the time of detection.
4. AT-Cut crystal or TXCO recommended.
Document No. 002-14804 Rev. *H
Page 21 of 50
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