CYW20704
6. Frequency References
The CYW20704 uses an external crystal for generating all radio frequencies and normal operation clocking. As an alternative, an
external frequency reference can be used.
6.1 Crystal Interface and Clock Generation
The CYW20704 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 crystal interfaced directly to the device
or an external frequency reference can be used.
Typical crystal frequencies of 20 MHz and 40 MHz are supported using the XTAL_STRAP_1 pin on the CYW20704. The signal char-
acteristics for the crystal interface are listed in Table 7 on page 19.
Table 7. Crystal Interface Signal Characteristics
Parameter
Acceptable frequencies
Crystal load capacitance
ESR
Crystal
19.2–52 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 1200
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
–
–
< –120
< –130
< –135
< –136
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
Tolerance without frequency
trimmingb
±20
±20
ppm
Initial frequency tolerance trimming ±50
range
±50
ppm
a. The frequency step size is approximately 80 Hz resolution.
b. AT-Cut crystal or TXCO recommended.
Document Number: 002-14786 Rev. *E
Page 19 of 49
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