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Data Sheet

ADF5610

Rev. 0 | Page 49 of 51

Example: Setting the Differential Output Divider to

Divide by 64 via the VCO Subsystem

The VCO registers are written in reverse order (highest to

lowest). First, set the divide ratio then enable the divider. Finally,

select the band.

To write 0 0000 0001 into VCO Register 0x02 (VCO_ID = 000b)

and set the VCO output divider to divide by 64, the following

must be written to Register 0x05 = 0 0000 0001 0010 000 =

0x0090:

•

subsystem address = 000b.

•

maximum output RF gain.

Next, use the same settings for Bits[14:0] in the Example:

Optimizing Power and Phase Noise Performance at RFOUT

Using the VCO Subsystem section for VCO Register 0x01. To

enable the differential output divider, simply change VCO

settings illustrate how settings for VCO Register 0x01 translate

to Register 0x05.

•

subsystem address = 000b.

•

address.

•

power, 5 dBm nominally.

•

performance mode.

•

divider (note that RFOUT power level drops by ~1 dBm).

If no VCO band change is required, register writes are complete.

Example: Changing Frequency after Configuring the

VCO

If writing to the synthesizer for the first time or if the user is

changing frequencies, a write to Register 0x05 = 0 to allow a

subsequent frequency change via autocalibration is required.

The last write in the PLL register sequence triggers the

frequency update. If an integer value results at the phase

detector input, the last write in the register sequence is PLL

input, the last write in the register sequence is PLL Register 0x04.

If the band for the desired RFOUT frequency (prior to division)

is already known, the VCO band can be written to directly via

VCO Register 0x00 by disabling the temperature controlled VT

calibration voltage and manually selecting the band via VCO

For example, assume that the desired RFOUT frequency prior

to division is 8 GHz and 8 GHz falls in Subband 205 (see Table 35)

when autocalibration is used at room temperature. First, set

VCO Register 0x02 = 0x0090 for divide by 64 and maximum

output power at PDIV_OUT and NDIV_OUT. Next, set VCO

RFOUT port and the optimal phase noise performance on all

ports. Lastly, configure the VCO Register 0x00 subsystem write

via PLL Register 0x05 = 1100110100000000 = 0xCD00. The

following are individual bit field settings used in Register 0x05

to achieve the write to VCO Register 0x00.

•

subsystem address = 000b.

•

address.

•

Subband 205 = Subband 77 of the lower VCO core (see

Table 35).

ADF5610 Datasheet(PDF) 49 Page - Analog Devices

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