2.6 R3 REGISTER

The R3 register is used to setup the RF R Divider ratio as well as several other control functions related to the RF synthesizer.

Reg

23

22

21

20

19

18

17

16

15

14

13

12

11

10

9876543210

DATA[20:0]

C2

C1

C0

R3

RF_

RST

RF_

P

RF_

CPP

RF_

CP[1:0]

RF_R[8:0]

RF_FD[6:0]

0

1

1

2.6.1 RF_FD[6:0] — Fractional Denominator, RF Synthesizer

In Fractional Mode, RF_FD[6:0] is used to specify the fractional denominator of the fractional part of the N counter value. Note

that in this mode, values below 32 are not supported. If a fractional denominator between 2 and 32 is desired, the same N counter

value can be achieved by multiplying the fractional numerator and denominator by some constant factor. For instance, 1/16 can

be expressed as 5/80.

In integer mode, the value represented by this bit multiplies both the RF_N and RF_R counter values. If both of these counter

sizes are sufficiently large, it is recommended to set this bit to one. If the counter sizes are too small, this bit can be used to extend

the counter range.

RF_FD[6:0]

RF_FD

Value

Integer Mode

Fractional Mode

[RF_OM = 0]

RF_OM = 1

0

128

128

1

1

Not Supported (Use Integer Mode Instead)

…

…

Not Supported ( Use a higher value )

32

32

32

33

33

33

34

34

34

……

…

127

127

127

Value

Fractional Mode

(RF_OM=1)

Integer Mode

(RF_OM=0)

R Divider Value

RF_R

RF_R x RF_FD

Complete N Divider Value

RF_N x RF_FN/RF_FD

RF_N x RF_FD + RF_FN

See R divider programming (section 2.6.2 ) and N divider programming (Section 2.7.2) for more detailed programming

information.

2.6.2 RF_R[8:0] — R Divider Ratio, RF Synthesizer

RF_R[8:0] is used to specify an integer value from 1 to 511 that is used in calculating the R divider ratio for the RF synthesizer.

In the case that the PLL is operating in fractional mode, the R counter value is simply the value represented by RF_R. However,

in integer mode, the R counter value is calculated by multiplying RF_R by the fractional denominator value.

R (Integer Mode) = RF_R x RF_FD

Since RF_R can take on integer values between 1 – 511 and RF_FD can take on integer values between 1 – 128, this value can

range from 1 - 65408, although prime values between 512 and 65,408 can not be realized.

RF_R[8:0]

RF_R

Value

0

Not Supported

11

……

511

511

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