ADF7021 datasheet(48/64 Pages) AD

48 / 64 page

ADF7021

Data Sheet

Rev. B | Page 48 of 64

RF R COUNTER

DIVIDE RATIO

X1 XTAL OSC

OFF

VA2

VA1

VCO CENTER

FREQ ADJUST

NOMINAL

VCO ADJUST UP 1

VCO ADJUST UP 2

VCO ADJUST UP 3

XTAL

DOUBLER

DISABLE

ENABLED

CP2

CP1

RSET

ICP (mA)

3.6k

Ω

0.3

0.9

1.5

2.1

VB4

VB3

VB2

VB1

VCO BIAS

CURRENT

0.25mA

0.5mA

3.75mA

CL4

CL3

CL2

CL1

CLKOUT

DIVIDE RATIO

OFF

VCO_BIAS

ADDRESS

BITS

XTAL_

BIAS

XB2 XB1

XTAL

BIAS

20µA

25µA

30µA

35µA

RFD1 RF DIVIDE BY 2

OFF

LOOP

CONDITION

VCO OFF

VCO ON

VE1

VCO

INTERNAL L VCO

EXTERNAL L VCO

VCL1

R_COUNTER

CLOCKOUT_

DIVIDE

Figure 63. Register 1—VCO/Oscillator Register Map

The R_COUNTER and XTAL_DOUBLER relationship is

expressed as follows:

If XTAL_DOUBLER = 0,

COUNTER

XTAL

PFD

If XT

AL_DOUBLER =1,

COUNTER

XTAL

PFD

The CLOCKOUT_DIVIDE is a divided-down and inverted

version of the XTAL and is available on Pin 36 (CLKOUT).

Set XOSC_ENABLE high when using an external crystal. If

using an external oscillator (such as TCXO) with CMOS-level

outputs into Pin OSC2, set XOSC_ENABLE low. If using an

external oscillator with a 0.8 V p-p clipped sine wave output

into Pin OSC1, set XOSC_ENABLE high.

The VCO_BIAS bits should be set according to Table 9.

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 RF_DIVIDE_BY_2 is enabled).

Setting VCO_INDUCTOR to external allows the use of the

external inductor VCO, which gives RF operating frequencies of

80 Hz to 650 MHz. If the internal inductor VCO is being used

for operation, set this bit low.

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