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ADF4193

Rev. B | Page 16 of 28

MOD/R REGISTER (R1)

DB23

DB22

DB21

DB20

DB19

DB18

DB17

DB16

DB15

DB14

M12

DB13

M11

DB12

M10

DB11

DB10

DB9

DB8

DB7

DB6

DB5

DB4

DB3

DB2

C3 (0)

DB1

C2 (0)

DB0

C1 (1)

4-BIT RF

R COUNTER

12-BIT MODULUS

CONTROL

BITS

NOMINAL

ADJUSTED

CP ADJ

DISABLE

ENABLE

REF/2

4/5

8/9

PRESCALER

DOUBLER DISABLED

DOUBLER ENABLED

DOUBLER ENABLE

M12

M11

M10

..........

INTERPOLATOR MODULUS VALUE (MOD)

4092

4093

4094

4095

RF R COUNTER DIVIDE RATIO

Figure 30. MOD/R Register (R1)

This register is used to set the PFD reference frequency and the

channel step size, which is determined by the PFD frequency

divided by the fractional modulus. Note that the MOD, R

counter, REF/2, CP ADJ, and doubler enable bits are double

buffered. They do not take effect until the next write to R0

(FRAC/INT register) is complete.

Control Bits

With C3, C2, and C1 set to 0, 0, 1, respectively, the MOD/R

CP ADJ

When this bit is set to 1, the charge pump current is scaled up

25% from its nominal value on the next write to R0. When this

bit is set to 0, the charge pump current stays at its nominal value

on the next write to R0. See the Programming section for more

information on how this feature can be used.

REF/2

Setting this bit to 1 inserts a divide-by-2, toggle flip-flop

between the R counter and PFD, which extends the maximum

REFIN input rate.

Reserved Bit

Reserved Bit DB21 must be set to 0.

Doubler Enable

Setting this bit to 1 inserts a frequency doubler between REFIN

and the 4-bit R counter. Setting this bit to 0 bypasses the

doubler.

4-Bit RF R Counter

It allows the REFIN frequency to be divided down to produce the

reference clock to the PFD. All integer values from 1 to 15 are

allowed. See the Worked Example section.

12-Bit Interpolator Modulus

For a given PFD reference frequency, the fractional denomina-

tor or modulus sets the channel step resolution at the RF

output. All integer values from 13 to 4095 are allowed. See the

Programming section for additional information and guidelines

for selecting the value of MOD.

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