LMX2486
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SNAS324 –JANUARY 2006
RF_N[10:0] -- RF N Counter Value
The RF N counter contains an 16/17/20/21 and a 32/33/36/37 prescaler. The N counter value can be calculated
as follows:
N = RF_P·RF_C + 4·RF_B + RF_A
RF_C ≥Max{RF_A, RF_B} , for N-2
FM
-1 ... N+2
FM
is a necessary condition. This rule is slightly modified in the
case where the RF_B counter has an unused bit, where this extra bit is used by the delta-sigma modulator for
the purposes of modulation. Consult the tables below for valid operating ranges for each prescaler.
Table 1. Operation with the 16/17/20/21 Prescaler (RF_P=0)
RF_N RF_N [10:0]
RF_C [5:0] RF_B [2:0] RF_A [1:0]
<49 N Values Below 49 are Illegal.
49-63 Legal Divide Ratios are:
2nd Order Modulator: 49-61
3rd Order Modulator: 51-59
4th Order Modulator: 55
64-79 Legal Divide Ratios are:
2nd and 3rd Order Modulator: All
4th Order Modulator: 64-75
80 0 0 0 1 0 1 0 0 0 0 0
... . . . . . . 0 . . . .
1023 1 1 1 1 1 1 0 1 1 1 1
>1023 N values above 1023 are prohibited.
Table 2. Operation with the 32/33/36/37 Prescaler (RF_P=1)
RF_N [10:0]
RF_N
RF_C [5:0] RF_B [2:0] RF_A [1:0]
<97 N Values Below 97 are Illegal.
97-226 Legal Divide Ratios are:
2nd Order Modulator: 97-109, 129-145, 161-181, 193-217, 225-226
3rd Order Modulator: 99-107, 131-143, 163-179, 195-215
4th Order Modulator: 103, 135-139, 167-175, 199-211
227-230 Legal Divide Ratios are:
2nd and 3rd Order Modulator: All
4th Order Modulator: None
231 0 0 0 1 1 1 0 0 1 1 1
... . . . . . . . . . . .
2039 1 1 1 1 1 1 1 0 1 1 1
2040- Possible with a second or third order delta-sigma engine.
2043
2044- Possible only with a second order delta-sigma engine.
2045
>2045 N values greater than 2045 are prohibited.
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