Methods and devices for multiple-mode radio frequency synthesizers

A circuit comprising:

• a digitally-controlled oscillator configured to generate an oscillator signal having an output frequency;
• a digital frequency locked-loop configured to control the output frequency of the oscillator signal in a first mode of operation based on a first control signal;
• a digital phase locked-loop configured to control the output frequency of the oscillator signal in a second mode of operation based on a second control signal;
• and
• a controller configured to:
• use a third mode of operation to control the output frequency of the oscillator signal, wherein the third mode of operation includes using a calibration loop to control the output frequency of the oscillator signal, the third mode being before the first mode of operation and the second mode of operation;
• determine whether to operate in the first mode or second mode of operation based on whether a value of a reference frequency signal exceeds a threshold;
• generate the first control signal based on the determination of operating in the first mode of operation;
• and
• generate the second control signal based on the determination of operating in the second mode of operation.