4.3.3 VCO

The VCO is designed to cover a frequency range of 1,672 MHz to 1,912 MHz to accommodate all operating frequency bands of the ATA8210/15.

To support this high frequency range, two digital settings of the VCO have to be set before using the oscillator in the analog PLL loop. These settings are the amplitude control FEVCO.VCOB[3:0] and the frequency control FEVCT.FEVCT[3:0].

The VCO amplitude is determined by FEVCO.VCOB[3:0]. Two parameters are used to calculate the FEVCO.VCOB[3:0] value. The first parameter comes from the factory-locked EEPROM, which compensates the process tolerances of the VCO. The second one is dependent on the actual output frequency and is stored in the EEPROM settings for each service. Use the configuration tool to calculate the required settings.

The content of the FEVCT[3:0] register is determined in an automated frequency tuning loop. For more details on the activation of the VCO tuning process, see VCO Tuning from Related Links. The processing time for the calibration routine is about 150 µs. The user needs to execute this calibration if the temperature changes by more than 40K or if the VCO frequency changes by more than 25 MHz.