Frequency tuning and step control of a digitally controlled oscillator

A method for tuning a digitally controlled oscillator, comprising:

• coarsely tuning a digitally controlled oscillator to a first frequency, wherein the frequency of the digitally controlled oscillator depends on an inductor and the total capacitance of one or more capacitive elements including a first and a second variable leaf capacitor, wherein the respective capacitances of the first and second variable leaf capacitors depend on a common-mode voltage applied to both of the first and second variable leaf capacitors and on a first bias voltage applied to the first variable leaf capacitor and a second bias voltage applied to the second variable leaf capacitor;
• setting the capacitive range of each of the first and second variable leaf capacitors to a first capacitive range by setting the common-mode voltage to a first common-mode voltage value, the first capacitive range corresponding to a first desired frequency range of the digitally controlled oscillator at the first frequency;
• providing the first bias voltage to a bias terminal of the first variable leaf capacitor with a variable voltage bias;
• finely tuning the digitally controlled oscillator to the first frequency by setting the first bias voltage to one of a first bias voltage setting and a second bias voltage setting;
• providing the second bias voltage to a bias terminal of the second variable leaf capacitor with an output of a digital-to-analog converter (DAC);
• and
• extra-finely tuning the digitally controlled oscillator to the first frequency by setting the second bias voltage to one of a plurality of bias voltage settings, the plurality of bias voltage settings ranging from approximately the first bias voltage setting to approximately the second bias voltage setting and comprising at least one intermediate setting between the first bias voltage setting and the second bias voltage setting.

A digitally controlled oscillator, comprising:

• a gain stage;
• an inductor;
• a first variable leaf capacitor having a first bias terminal and a first pair of common-mode terminals, a capacitance of the first variable leaf capacitor dependent on voltages at the first bias terminal and the first pair of common-mode terminals;
• a second variable leaf capacitor having a second bias terminal and a second pair of common-mode terminals, a capacitance of the second variable leaf capacitor dependent on voltages at the second bias terminal and the second pair of common-mode terminals;
• a common-mode voltage bias configured to drive the first pair of common mode terminals of the first variable leaf capacitor and the second pair of common mode terminals of the second variable leaf capacitor;
• a variable voltage bias coupled to the first bias terminal of the first variable leaf capacitor and configured to drive the first bias terminal to one of a first bias voltage and a second bias voltage to tune the digitally controlled oscillator;
• and
• a digital-to-analog converter coupled to the second bias terminal of the second variable leaf capacitor and configured to drive the second bias terminal to one of a plurality of bias voltage settings to further tune the digitally controlled oscillator, the plurality of bias voltage settings ranging from approximately the first bias voltage to approximately the second bias voltage and comprising at least one intermediate setting between the first bias voltage and the second bias voltage.