Datasheet
ADF4159 Data Sheet
Rev. D | Page 16 of 36
LSB FRAC REGISTER (R1) MAP
When Bits DB[2:0] are set to 001, the on-chip LSB FRAC
register (Register R1) is programmed (see Figure 26).
Reserved Bits
All reserved bits must be set to 0 for normal operation.
Phase Adjustment
Bit DB28 enables and disables phase adjustment. The phase
shift is generated by the value programmed in Bits DB[14:3].
13-Bit LSB Fractional Value (FRAC)
Bits DB[27:15], along with Bits DB[14:3] in the FRAC/INT
register (Register R0), set the FRAC value that is loaded into
the fractional interpolator. The FRAC value forms part of the
overall feedback division factor.
These 13 bits are the least significant bits (LSBs) of the 25-bit
FRAC value; Bits DB[14:3] in the FRAC/INT register are the
most significant bits (MSBs). For more information, see the
RF Synthesizer Worked Example section.
12-Bit Phase Value
Bits DB[14:3] control the phase word. The phase word is used
to increase the RF output phase relative to the current phase.
The phase change occurs after a write to Register R0.
Phase Shift = (Phase Value × 360°)/2
12
For example, Phase Value = 512 increases the phase by 45°.
To u se phase adjustment, Bit DB28 must be set to 1. If phase
adjustment is not used, it is recommended that the phase value
be set to 0.
DB31
CONTROL
BITS
12-BIT PHASE VALUE
13-BIT LSB FRACTIONAL VALUE
(FRAC)
RESERVED
DB30
DB29 DB28 DB27
DB26 DB25
DB24 DB23
DB22
DB21 DB20
DB19 DB18
DB17 DB16 DB15
DB14 DB13
DB12 DB11
DB10
DB9 DB8
DB7
DB6 DB5 DB4
DB3 DB2
DB1
DB0
0
0 0
P1 F13
F12
F11 F10 F9 F8
F7 F6
F5
F4 F3
F2 F1
P12
P11 P10 P9 P8
P7
P6 P5
P4 P3
P2
P1 C3(0)
C2(0) C1(1)
P12 P
11 ...
P2 P1 PHASE VALUE
0
1 ... 1
1 2047
. .
... .
. .
0
0 ...
1 1 3
0 0
... 1 0 2
0
0 ...
0 1 1
0
0 ... 0 0
0 (RECOMMENDED)
1
1 ... 1
1 –1
1
1 ... 1
0 –2
1 1 ...
0 1 –3
. .
... . . .
1
0 ... 0
0 –2048
*THE FRAC VALUE IS MADE UP OF THE 12-BIT MSB STORED IN
REGISTER R0 AND THE 13-BIT LSB STORED IN REGISTER R1.
FRAC VALUE = 13-BIT LSB + 12-BIT MSB × 2
13
.
DBB
DBB
NOTES
1. DBB = DOUBLE-BUFFERED BITS.
10849-021
PHASE ADJ
P1
PHASE ADJ
0
DI
SA
BLE
D
1
EN
AB
LED
F13
F12 ...
F2 F1
LSB FRACTIONAL VALUE
(FRAC)*
0
1
2
3
.
.
.
8188
8189
8190
8191
0
0
0
0
.
.
.
1
1
1
1
0
0
0
0
.
.
.
1
1
1
1
...
...
...
...
...
...
...
...
...
...
...
0
0
1
1
.
.
.
0
0
1
1
0
1
0
1
.
.
.
0
1
0
1
Figure 26. LSB FRAC Register (R1) Map