AD9148BPCZ AD [Analog Devices], AD9148BPCZ Datasheet - Page 58

• Manufacturer Part Number: AD9148BPCZ
• Description: Quad 16-Bit,1 GSPS, TxDAC+ Digital-to-Analog Converter
• Manufacturer: AD [Analog Devices]

AD9148
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:
1.
2.
3.
4.
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.
Rev. PrA | Page 58 of 73
The resulting VCO band should be the optimal setting for the
device. This band should be written to the manual VCO band
register value.
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
1111
1110
1101
1100
1011
1010
1001
1000
0111
0110
0101
0100
0011
0010
0001
0000
Preliminary Technical Data
Indication
Move to higher VCO band
VCO is operating in the higher end of
frequency band
VCO is operating with an optimal region
of the frequency band
VCO is operating in the lower end of
frequency band
Move to lower VCO band