AK2401 Datasheet, PDF (41/103 Pages) Asahi Kasei Microsystems – Direct Conversion Transceiver

[AK2401]
Example2) When offset frequency is positive value (2):
If Frequency Setting = 490.0375MHz, PFD Frequency = 2.4MHz
INT=204, FRAC= 47775 and MOD= 262080,
Frequency Setting = 2.4 × (204 + 47775 / 262080) = 490.037500000… [MHz]
To obtain 100Hz Offset Frequency,
OFST = 100 / 2400000 × 262080 = 10.92
The setting value will be 11(dec) = 0x0000B(hex) by rounding off OFST
Therefore, the actual Offset Frequency is as follows
Offset Frequency = 2400000 × 11 / 262080 = 100.7 [Hz]
In this case, offset error is 0.7Hz.
Example3) When offset frequency is negative value:
If Frequency Setting = 490.0375MHz, PFD Frequency = 2.4MHz
INT=204, FRAC= 47775 and MOD= 262080,
Frequency Setting = 2.4 × (204 + 47775 / 262080) = 490.037500000… [MHz]
To obtain 100Hz Offset Frequency,
OFST = -100 / 2400000 × 262080 = -10.92
The setting value will be -11(dec) = 0x3FFF5(hex) by rounding off OFST
Therefore, the actual Offset Frequency is as follows
Offset Frequency = 2400000 × (-11) / 262080 = -100.7 [Hz]
In this case, offset error is 0.7Hz.
FRAC
OFST
FRACX = FRAC+OFST
FRAC_recal ：Recalculated Fractional Setting
INT_recal ：Recalculated Integer Setting
no
no
FRACX < 0
FRACX > MOD
yes
yes
FRAC_recal = FRACX+MOD
INT_recal = INT-1
FRAC_recal = FRACX-MOD
INT_recal = INT+1
FRAC_recal=FRACX
INT_recal = INT
Figure 24. Frequency Recalculation Flow Chart with OFST Register Setting
017003093-E-00
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