AD9148BBCZ datasheet(58/73 Pages) AD

58 / 73 page

AD9148

Preliminary Technical Data

Rev. PrA | Page 58 of 73

Automatic VCO Band Select

The device has an automatic VCO band select feature on chip;

using this feature is a simple and reliable method for configuring

the VCO frequency band. To use the automatic VCO band select

feature, enable the PLL by writing 0xC0 to Register 0x0A and

enable the auto band select mode by writing 0x80 to Register 0x0A.

When this value is written, the device executes an automated

routine that determines the optimal VCO band setting for the

device. The setting selected by the device ensures that the PLL

remains locked over the full −40°C to +85°C operating temperature

range of the device without further adjustment. (The PLL remains

locked over the full temperature range even if the temperature

during initialization is at one of the temperature extremes.)

Manual VCO Band Select

The device also has a manual band select mode that allows the

user to select the VCO tuning band. When in manual mode

(enabled by setting Bit 6, Register 0x0A to 1), the VCO band is

set directly with the value written to the manual VCO band bit

enabled (Bits[5:0], Register 0x0A). To properly select the VCO

band, do the following sequence:

Put device in manual band select mode.

Sweep the VCO band over a range of bands that result in

the PLL being locked.

Verify that the PLL is locked and read the VCO control

voltage for each band.

Select the band that results in the control voltage being

closest to the center of the range (that is, 1000). See Table 25

for more details.

The resulting VCO band should be the optimal setting for the

device. This band should be written to the manual VCO band

If desired, an indication of where the VCO is within the

operating frequency band can be determined by querying the

VCO control voltage. Table 25 shows how to interpret the VCO

control voltage value.

Table 25. VCO Control Voltage Range Indications

VCO Control Voltage

Indication

1111

Move to higher VCO band

1110

1101

VCO is operating in the higher end of

frequency band

1100

1011

1010

1001

VCO is operating with an optimal region

of the frequency band

1000

0111

0110

0101

VCO is operating in the lower end of

frequency band

0100

0011

0010

0001

Move to lower VCO band

0000

AD9148BBCZ Datasheet(PDF) 58 Page - Analog Devices

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