ADRF6655ACPZ-R7 datasheet(33/44 Pages) AD

33 / 44 page

ADRF6655

Rev. 0 | Page 33 of 44

With R6[2:0] set to 111, the external VCO control register is

programmed as shown in Figure 77.

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 phase noise of the VCO is higher

than desired. By setting the external VCO enable bit (DB22) to 1,

and setting Bit DB15 to Bit DB10 of Register 6 to 0, the internal

VCO is disabled and the output of an external VCO can be fed into

the part differentially 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, tuning voltage

pin of the VCO. See the Using an External VCO section for more

information.

DB23

DB22

DB21 DB20 DB19 DB18 DB17 DB16 DB15 DB14 DB13 DB12 DB11 DB10 DB9

DB8

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

0XVCO

EXTERNAL

VCO

ENABLE

RES

0000

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

RESERVED

CONTROL BITS

XVCO

INTERNAL VCO

EXTERNAL VCO

EXTERNAL VCO ENABLE

Figure 77. External VCO Control Register (R7)

ADRF6655ACPZ-R7 Datasheet(PDF) 33 Page - Analog Devices

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