Datasheet

AD9148 Data Sheet
Rev. B | Page 58 of 72
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, complete the following sequence:
1. Put the device in manual band select mode.
2. Sweep the VCO band over a range of bands that results in
the PLL being locked.
3. Verify that the PLL is locked and read the VCO control
voltage for each band.
4. Select the band that results in the control voltage being
closest to the center of the range (that is, 1000). See Table 26
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
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 26 shows how to interpret the VCO
control voltage value.
Table 26. VCO Control Voltage Range Indications
VCO Control Voltage Indication
1111 Move to a 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 a lower VCO band.
0000