Data Sheet

ADRF6701

Rev. 0 | Page 27 of 36

REGISTER 6—VCO CONTROL AND VCO ENABLE

(DEFAULT: 0X1E2106)

With Register 6, Bits[2:0] set to 110, the VCO control and

enable register is programmed as shown in Figure 47.

The VCO tuning band is normally selected automatically by the

band calibration algorithm, although the user can directly select

the VCO band using Register 6.

The VCO BSSRC bit (DB9) determines whether the result of

the calibration algorithm is used to select the VCO band or if

the band selected is based on the value in VCO band select

(DB8 to DB3).

The VCO amplitude can be controlled through Register 6. The

VCO amplitude setting can be controlled between 0 and 63. The

default value of 8 should be set to a recommended value of 63.

The internal VCOs can be disabled using Register 6.

The internal charge pump can be disabled through Register 6.

By default, the charge pump is enabled.

To turn off the PLL (for example, if the ADRF6701 is being

driven by an external LO), set Register 6, Bits[20:17] to zero.

REGISTER 7—EXTERNAL VCO ENABLE AND

SECOND LO DIVIDER

With Register 7, Bits[2:0] set to 111, the external VCO control

register is programmed as shown in Figure 48.

The external VCO enable bit allows the use of an external VCO

in the PLL instead of the internal VCO. This can be advantageous

in cases where the internal VCO is not capable of providing the

desired frequency or where the internal VCO’s phase noise is

higher than desired. By setting this bit (DB22) to 1, and setting

Register 6, Bits[15:10] to 0, the internal VCO is disabled, and

the output of an external VCO can be fed into the part differ-

entially on Pin 38 and Pin 37 (LOP and LON). Because the loop

filter is already external, the output of the loop filter simply

needs to be connected to the external VCO’s tuning voltage pin.

In addition, Register 7 provides control over a divide-by-2 block

in the LO path using Bit DB4. If DB4 is set to 1, then the divide-

by-2 block is bypassed, and an external 2× LO can be used to

drive the modulator.

CHARGE

PUMP

ENABLE

3.3V

LDO

ENABLE

VCO

ENABLE

VCO

SWITCH

VCO

BW SW

CTRL

VBSRC

0

1

VCO EN

VCO LDO

ENABLE

VCO AMPLITUDE

RESERVED

VCO BAND SELECT FROM SPI

VBS[5:0] VCO BAND SELECT FROM SPI

0x00

DEFAULT 0x20

CHARGE PUMP ENABLE

0x01

….

0x00

0

….

….

0x08

8 (DEFAULT)

….

….

0x2B

43

….

….

0x3F

63 (RECOMMENDED)

0x3F

VCO BW CAL AND SW SOURCE CONTROL

BAND CAL (DEFAULT)

VCO SW

0

1

VCO SWITCH CONTROL FROM SPI

REGULAR (DEFAULT)

BAND CAL

SPI

VCO ENABLE

DISABLE

ENABLE (DEFAULT)

DB22 DB21

DB20

DB19

DB18

DB17

DB16

DB15 DB14 DB13 DB12 DB11 DB10

DB9

DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0

CONTROL BITS

DB23

CPEN

L3EN

VCO EN VCO SW VC5 VC4 VC3 VC2 VC1 VC0 VBSRC VBS5 VBS4 VBS3 VBS2 VBS1 VBS0 C3(1) C2(1) C1(0)

LVEN

VC[5:0] VCO AMPLITUDE

0

1

LVEN

VCO LDO ENABLE

DISABLE

ENABLE (DEFAULT)

0

1

L3EN 3.3V LDO ENABLE

DISABLE

ENABLE (DEFAULT)

0

1

CPEN

DISABLE

ENABLE (DEFAULT)

0

1

00

0

Figure 47. Register 6—VCO Control and VCO Enable Register Map

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

XVCO

EXTERNAL

VCO

ENABLE

RES

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

C3(1) C2(1) C1(1)

RESERVED

CONTROL BITS

XVCO

0

1

INTERNAL VCO (DEFAULT)

EXTERNAL VCO

EXTERNAL VCO ENABLE

LDIV2

0

1

DIVIDE BY 4 (DEFAULT)

LO PATH DIVIDE RATIO

DIVIDE BY 2

Figure 48. Register 7—External VCO Enable Register Map