Preliminary Technical Data

ADF7021

Rev. PrI | Page 29 of 44

REGISTER 1—VCO/OSCILLATOR REGISTER

R3

R2

R1

RF R COUNTER

DIVIDE RATIO

0

0

.

.

.

1

1

2

.

.

.

7

1

0

.

.

.

1

0

1

.

.

.

1

X1 XTAL OSC

0OFF

1ON

VA2

VA1

VCO CENTER

FREQ ADJUST

0

NOMINAL

0

VCO ADJUST UP 1

1

VCO ADJUST UP 2

1

0

1

0

1

VCO ADJUST UP 3

D1

XTAL

DOUBLER

0

DISABLE

ENABLED

1

CP2

CP1

RSET

00

0.3

01

0.9

10

1.5

11

2.1

VB4

VB3

VB2

VB1

VCO BIAS

CURRENT

00.25mA

00.5mA

.

1

1

0

.

1

0

1

.

1

0

0

.

14mA

CL4

CL3

CL2

CL1

DIVIDE RATIO

0

OFF

0

0

.

.

.

1

0

1

0

.

.

.

1

2

4

.

.

.

0

0

1

.

.

.

1

0

0

0

.

.

.

1

30

VCO BIAS

CLOCKOUT

DIVIDE

ADDRESS

BITS

RCOUNTER

XTAL

BIAS

XB2 XB1

XTAL

BIAS

1

0

1

0

0

÷2 OFF

÷2 ON

1

LOOP

CONDITION

VCO OFF

VCO ON

VE1

0

1

VCO

INDUCTOR

INTERNAL

EXTERNAL

VCL1

0

1

Figure 33.

Register 1—VCO/Oscillator Register N Comments

•

R_DIVIDE and XTAL DOUBLER

If XTAL DOUBLER = 0,

DIVIDE

_

R

XTAL

PFD

=

If XTAL DOUBLER =1,

DIVIDE

_

R

XTAL

PFD

2

×

=

•

CLOCKOUT is a divided-down version of the XTAL and is available on Pin 36 (CLKOUT).

•

XOSC_ENABLE should be set high when using an external crystal. If using an external oscillator (such as TCXO, OCXO) with

CMOS-level outputs into Pin OSC2, the XOSC enable should be set low.

•

The VCO_ADJUST bits adjust the center of the VCO operating band. Each bit typically adjusts the VCO band up by 1% of the RF

operating frequency (0.5% if divide-by-2 is enabled).

•

Setting VCO_INDUCTOR to external allows the use of an external VCO tank inductor, which gives RF operating frequencies of

80 Hz to 650 MHz. If the internal inductor is being used for operation, this bit should be set low.