ADF5355

Data Sheet

Rev. A | Page 22 of 38

Figure 41. Register 0

REGISTER 0

Control Bits

With Bits[C4:C1] set to 0000, Register 0 is programmed. Figure 41

shows the input data format for programming this register.

Reserved

Bits[DB31:DB22] are reserved and must be set to 0.

Automatic Calibration (AUTOCAL)

Write to Register 0 to enact (by default) the VCO automatic

calibration, and to choose the appropriate VCO and VCO

subband. Write 1 to the AC1 bit (Bit DB21) to enable the

automatic calibration, which is the recommended mode of

operation.

Set the AC1 bit (Bit DB21) to 0 to disable the automatic

calibration, which leaves the ADF5355 in the same band it was

already in when Register 0 is updated.

Disable the automatic calibration only for fixed frequency

applications, phase adjust applications, or very small (<10 kHz)

frequency jumps.

Toggling AUTOCAL is also required when changing frequency.

See the Frequency Update Sequence section for more information.

Prescaler Value

The dual modulus prescaler (P/P + 1), along with the INT,

FRACx, and MODx counters, determines the overall division

ratio from the VCO output to the PFD input. The PR1 bit

(Bit DB20) in Register 0 sets the prescaler value.

Operating at CML levels, the prescaler takes the clock from the

VCO output and divides it down for the counters. It is based on

a synchronous 4/5 core. When the prescaler is set to 4/5, the

maximum RF frequency allowed is 7 GHz. The prescaler limits

16-Bit Integer Value

The 16 INT bits (Bits[DB19:DB4]) set the INT value, which

determines the integer part of the feedback division factor. The

INT value is used in Equation 3 (see the INT, FRAC, MOD, and

R Counter Relationship section). All integer values from 23 to

32,767 are allowed for the 4/5 prescaler. For the 8/9 prescaler,

the minimum integer value is 75, and the maximum value is

65,535.

N16

N15

...

N5

N4

N3

N2

N1

INTEGER VALUE (INT)

00

...

00

00

0

NOT ALLOWED

00

...

00

00

1

NOT ALLOWED

00

...

00

01

0

NOT ALLOWED

..

...

..

..

.

...

00

...

10

11

0

NOT ALLOWED

00

...

10

11

1

23

00

...

11

00

0

24

..

...

..

..

.

...

1

1

...

1

1

1

0

1

65533

1

1

...

1

1

1

1

0

65534

1

1

...

1

1

1

1

1

65535

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

N16

N15

N14

N13

N12

N11

N10

N9

RESERVED

16-BIT INTEGER VALUE (INT)

CONTROL

BITS

N8

N7

N6

N5

N4

N3

N2

N1

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

INTMIN = 75 WITH PRESCALER = 8/9

PR1

PRESCALER

04/5

18/9

PR1

AC1

0

0

0

0

0

0

0

0

0

0

C1(0)

DB31

AC1

VCO

AUTOCAL

0

DISABLED

1

ENABLED