Single differential-inductor VCO with implicit common-mode resonance

1. A circuit for a single differential-inductor oscillator with common-mode resonance, the circuit comprising:

a tank circuit formed by coupling a first inductor with a pair of first capacitors;

a cross-coupled transistor pair coupled to the tank circuit; and

one or more second capacitors coupled to the tank circuit and the cross-coupled transistors,

wherein the single differential-inductor oscillator is configured to allow tuning of a common mode (CM) resonance frequency (F CM ) associated with the single differential-inductor oscillator to be at twice a differential resonance frequency (F D ) associated with the single differential-inductor oscillator.

2. The circuit of claim 1 , wherein the single differential-inductor oscillator comprises a voltage-controlled oscillator (VCO), and wherein the single differential-inductor oscillator is configured to allow tuning the F CM associated with the single differential-inductor oscillator to be at twice the F D associated with the single differential-inductor oscillator by adjusting a ratio of capacitance values of the first and second capacitors.

3. The circuit of claim 1 , wherein the first inductor comprises a coupled inductor pair that is realized as a spiral inductor having an inner loop that is smaller than an outer loop.

4. The circuit of claim 1 , wherein the first pair of capacitors is realized by a differential switch capacitance circuit comprising a plurality of differential switch capacitance unit cells.

5. The circuit of claim 4 , wherein each of the plurality of differential switch capacitance unit cells is realized by two capacitors and a variable capacitance associated with a deep N-well device, having inherent junction diodes, that is biased by using high impedance supplies.

6. The circuit of claim 1 , wherein the one or more second capacitors are realized by a CM capacitance tuning circuit comprising a plurality of CM capacitance tuning unit cells.

7. The circuit of claim 6 , wherein each of the plurality of CM capacitance tuning unit cells is realized by two capacitors having a common node coupled through a switch to ground potential.

8. The circuit of claim 1 , wherein the single differential-inductor oscillator is configured to allow tuning of the F CM associated with the single differential-inductor oscillator independent of the F D associated with the single differential-inductor oscillator.

9. The circuit of claim 1 , wherein the single differential-inductor oscillator is configured to allow maximizing a value of a CM impedance at the F CM associated with the single differential-inductor oscillator.

10. The circuit of claim 1 , wherein the single differential-inductor oscillator is configured to maximize values of phase noise per unit power for multiple frequency offsets at a point that corresponds to an optimum ratio of capacitance values of the first and second capacitors, wherein the multiple frequency offsets are measured from a resonance frequency of the single differential-inductor oscillator, and wherein the optimum ratio of capacitance values of the first and second capacitors corresponds to the F CM associated with the single differential-inductor oscillator being twice the F D associated with the single differential-inductor oscillator.

11. A method for providing a single differential-inductor oscillator with common-mode resonance, the method comprising:

forming a tank circuit by coupling a first inductor with a pair of first capacitors;

coupling a cross-coupled transistor pair to the tank circuit;

coupling one or more second capacitors to the tank circuit and the cross-coupled transistors; and

configuring the single differential-inductor oscillator to allow tuning of a common mode (CM) resonance frequency (F CM ) associated with the single differential-inductor oscillator to be at twice a differential resonance frequency (F D ) associated with the single differential-inductor oscillator.

12. The method of claim 11 , wherein configuring the single differential-inductor oscillator comprises configuring a voltage-controlled oscillator (VCO), and wherein the method further comprises configuring the single differential-inductor oscillator to allow tuning of the F CM associated with the single differential-inductor oscillator to be at twice the F D associated with the single differential-inductor oscillator by adjusting a ratio of capacitance values of the first and second capacitors.

13. The method of claim 11 , wherein forming a tank circuit is performed by coupling, with a pair of first capacitors, a coupled inductor pair that is realized as a spiral inductor having an inner loop that is smaller than an outer loop.

14. The method of claim 11 , further comprising implementing the first pair of capacitors by a differential switch capacitance circuit comprising a plurality of differential switch capacitance unit cells.

15. The method of claim 14 , further comprising implementing each of the plurality of differential switch capacitance unit cells by coupling two capacitors and a variable capacitance associated with a deep N-well device with inherent junction diodes, and biasing the deep N-well device by using high impedance supplies.

16. The method of claim 11 , further comprising implementing the one or more second capacitors by a CM capacitance tuning circuit comprising a plurality of CM capacitance tuning unit cells, and realizing each of the plurality of CM capacitance tuning unit cells by two capacitors having a common node coupled through a switch to ground potential.

17. The method of claim 11 , further comprising:

configuring the single differential-inductor oscillator to allow tuning of the F CM associated with the single differential-inductor oscillator independent of the F D associated with the single differential-inductor oscillator; and

configuring the single differential-inductor oscillator to maximize a value of a CM impedance at the F CM associated with the single differential-inductor oscillator.

18. The method of claim 11 , further comprising configuring the single differential inductor to maximize values of phase noise per unit power for multiple frequency offsets at a point that corresponds to an optimum ratio of capacitance values of the first and second capacitors, wherein the multiple frequency offsets are measured from a resonance frequency of the single differential-inductor oscillator, and wherein the optimum ratio of capacitance values of the first and second capacitors corresponds to the F CM associated with the single differential-inductor oscillator being twice the F D associated with the single differential-inductor oscillator.

19. A communication device comprising:

a radio-frequency (RF) transceiver comprising one or more local oscillators;

the one or more local oscillators comprising one or more single differential-inductor voltage-controlled oscillators (VCOs) with common-mode resonances, wherein each single differential-inductor VCO comprises:

a tank circuit formed by coupling a first inductor with a pair of first capacitors;

a cross-coupled transistor pair coupled to the tank circuit; and

one or more second capacitors coupled to the tank circuit and the cross-coupled transistors,

wherein each single differential-inductor VCO is configured to allow tuning of a common mode (CM) resonance frequency (F CM ) associated with the single differential-inductor VCO to be at twice a differential resonance frequency (F D ) associated with the single differential-inductor VCO.

20. The communication device of claim 19 , wherein the single differential-inductor VCO is configured to allow tuning of the F CM associated with the single differential-inductor VCO to be at twice the F D associated with the single differential-inductor VCO by adjusting a ratio of capacitance values of the first and second capacitors.