LMX2364 National Semiconductor Corporation, LMX2364 Datasheet - Page 30

• Manufacturer Part Number: LMX2364
• Description: 2.6 Ghz Pllatinum Fractional Rf Frequency Synthesizer With 850 Mhz Integer If Frequency Synthesizer
• Manufacturer: National Semiconductor Corporation

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Reg
R4
Programming Description
2.7 R4 REGISTER
This register is used to setup the N divider for the RF Synthesizer. A single word write to this register is all that is required to power
up and tune the RF synthesizer to the desired frequency.
2.7.1 RF_FN — Fractional Numerator, RF Synthesizer
In the case that the PLL is operating in fractional mode (RF_OM=1), RF_FN[6:0] specifies the fractional numerator of the
complete N counter value of the RF PLL. In the case that the PLL is operating in integer mode (RF_OM=0), RF_FN adds to the
total value of the N counter.
2.7.2 RF_N[12:0] — N Divider Ratio, RF Synthesizer
RF_N[12:0] specifies an integer value that is used in calculating the N divider ratio for the RF synthesizer. In the case the part is
operating in fractional mode, it value is the N divider ratio. In the case the part is operating in integer mode, this number is used
in conjunction with the RF_FD and RF_FN values to calculate the N divider value. The range of values supported is dependant
on the selected prescaler. When the 8/9/12/13 prescaler is selected, RF_N value can range from 40 to 4095. When the
16/17/20/21 prescaler is selected, the RF_N value can range from 80 to 8191. The following tables describe how to program a
specific value of RF_N for a given prescaler.
The RF_N value is actually created using a prescaler, C counter, B counter, and an A counter. If RF_P = 16, then the RF_N[12:0]
word is just the binary representation of the desired value. If RF_P = 8, then the case is similiar, except that the third LSB is
disregarded in all calculations. The relationship between RF_N, RF_P, RF_A, RF_B, and RF_C is shown below.
RF_N[12:0] Programming with RF_P = 16
RF_N[12:0] Programming with RF_P = 8
48–79
24–39
0–47
8191
0–23
4095
RF_
PD
23
80
81
…
40
41
…
22
Some of these N values are allowed, others are illegal divide ratios and not allowed.
Legal Divide Ratios in Fractional Mode: 48–49, 52–53, 64–66, 68–70, 72–74, 76–78
Legal Divide Ratios in Integer Mode: All these values are legal in integer mode.
Some of these N values are allowed, others are illegal divide ratios and not allowed.
Legal Divide Ratios in Fractional Mode: 24–25, 28–29, 32–34, 36–38
Legal Divide Ratios in Integer Mode: All these values are legal in integer mode.
12
12
0
0
1
0
0
1
21
Fractional Mode (RF_OM=1)
Integer Mode (RF_OM=0)
20
Operating Mode
11
11
0
0
1
0
0
1
19
18
10
10
0
0
1
0
0
1
17
RF_N[12:0]
9
0
0
1
9
0
0
1
16
RF_C[8:0]
RF_C[8:0]
RF_N = RF_PxRF_C +4xRF_B + RF_A
(Continued)
15
8
0
0
1
8
0
0
1
14
DATA[20:0]
Values from 0–47 are not allowed.
Values from 0–23 are not allowed.
7
0
0
1
7
0
0
1
13
12
30
RF_N[12:0]
RF_N[12:0]
6
1
1
1
6
0
0
1
11
5
0
0
1
5
1
1
1
10
RF N Divider Value Calculation
9
4
1
1
1
4
1
1
1
RF_N x RF_FD + RF_FN
RF_N +RF_FN/RF_FD
8
3
0
0
1
X
X
X
7
3
RF_FN[6:0]
RF_B [1:0]
RF_B[1:0]
6
2
0
0
1
2
0
0
1
5
4
1
0
0
1
1
0
0
1
3
RF_A[1:0]
RF_A[1:0]
C2
2
1
C1
0
0
1
1
0
0
1
1
1
0
C0
0
0