ADF5355

Data Sheet

Rev. A | Page 28 of 38

Figure 47. Register 6

REGISTER 6

Control Bits

With Bits[C4:C1] set to 0110, Register 6 is programmed. Figure 47

shows the input data format for programming this register.

Reserved

Bit DB31 is reserved and must be set to 0.

Gated Bleed

Bleed currents can be used for improving phase noise and spurs;

however, due to a potential impact on lock time, the gated bleed

bit, BL10 (Bit DB30), if set to 1, ensures bleed currents are not

switched on until the digital lock detect asserts logic high. Note

that this function requires digital lock detect to be enabled.

Negative Bleed

Use of constant negative bleed is recommended for most

fractional-N applications because it improves the linearity of

the charge pump, leading to lower noise and spurious signals than

leaving it off. To enable negative bleed, write 1 to BL9 (Bit DB29),

and to disable negative bleed, write 0 to BL9 (Bit DB29).

Reserved

Bit DB28 is reserved and must be set to 1. Bits[DB27:DB25] are

reserved and must be set to 010.

Feedback Select

D13 (Bit DB24) selects the feedback from the output of the

VCO to the N counter. When D13 is set to 1, the signal is taken

directly from the VCO. When this bit is set to 0, the signal is

taken from the output of the output dividers. The dividers

enable coverage of the wide frequency band (3.4 GHz to 6.8 GHz).

When the divider is enabled and the feedback signal is taken

from the output, the RF output signals of two separately

configured PLLs are in phase. Divided feedback is useful in

some applications where the positive interference of signals is

required to increase the power.

Divider Select

D12 to D10 (Bits[DB23:DB21]) select the value of the RF output

divider (see Figure 47).

D3

0

DISABLED

1

ENABLED

RF

OUTPUT

POWER

DB31 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

00

1

0

D13

D12

D11

D10

BL1

0

D8

D7

0

0

0

D3

D2

D1

C4(0) C3(1) C2(1)

CONTROL

BITS

CHARGE PUMP BLEED CURRENT

RF DIVIDER

SELECT1

RESERVED

D2

D1

OUTPUT POWER

0

0

–4dBm

0

1

–1dBm

10+2dBm

11+5dBm

D7

0

OFF

1

ON

D8

MUTE TILL

LOCK DETECT

0

MUTE DISABLED

1

MUTE ENABLED

D13

FEEDBACK

SELECT

0

FUNDAMENTAL

1

DIVIDED

C1(0)

D12

D11

RF DIVIDER SELECT

00

÷1

00

÷2

01

÷4

01

÷8

D10

0

1

0

1

1

1

1

0

0

1

÷16

÷32

÷64

0

1

0

BL8

BL7

..........

..........

..........

..........

..........

..........

..........

..........

..........

..........

BL2

BL1 BLEED CURRENT

0

0

0

1

1

(3.75µA)

0

0

1

0

2

(7.5µA)

..

.

.

.

..

.

.

.

..

.

.

.

1

1

0

0

(945µA)

252

1

1

0

1

253

(948.75µA)

1

1

1

0

254

(952.5µA)

1

1

1

1

255

(956.25µA)

BL2

BL3

BL4

BL5

BL6

BL7

BL8

BL9

BL9 NEGATIVE BLEED

0

ENABLED

1

DISABLED

RESERVED

1

BL10 GATED BLEED

0

ENABLED

1

DISABLED

BL10