CYW20702
6. Frequency References
The CYW20702 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 CYW20702 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 5.
Table 5. Crystal Interface Signal Characteristics
Parameter
Acceptable frequencies
Crystal load capacitance
ESR
Crystal
12–52 MHz in 2 ppma steps
12 (typical)
External Frequency Reference
12–52 MHz in 2 ppma steps
Units
–
N/A
–
pF
60 (max)
Ω
Power dissipation
Input signal amplitude
200 (max)
–
μW
mVp-p
N/A
400 to 2000
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
MΩ
≤ 2
pF
Phase noise
@ 1 kHz
@ 10 kHz
@ 100 kHz
@ 1 MHz
N/A
N/A
N/A
N/A
N/A
–
–
< –120b
< –131b
< –136b
< –136b
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
Auto-detection frequencies when
using external LPOc
12, 13, 14.4, 15.36, 16.2, 16.8, 18,
19.2, 19.44, 19.68, 19.8, 20, 24, 26,
33.6, 37.4, and 38.4
12, 13, 14.4, 15.36, 16.2, 16.8, 18,
19.2, 19.44, 19.68, 19.8, 20, 24, 26,
33.6, 37.4, and 38.4
MHz
Tolerance without frequency trimmingd ±20
±20
±50
ppm
ppm
Initial frequency tolerance trimming
range
±50
a. The frequency step size is approximately 80 Hz resolution.
b. With a 26 MHz reference clock. For a 13 MHz clock, subtract 6 dB. For a 52 MHz clock, add 6 dB.
c. 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.
d. AT-Cut crystal or TXCO recommended.
Document Number: 002-14773 Rev. *L
Page 23 of 55
CYPRESS [ CYPRESS ]
