Quadrature hybrid with variable capacitor tuning network

1. A quadrature hybrid comprising:

a first port;

a second port;

a third port;

a fourth port;

first, second, and third inductors;

first, second, third, and fourth capacitors; and

a first variable capacitor tuning network connected between the first port and the fourth port;

a second variable capacitor tuning network connected between the second port and the third port; and

wherein:

the first and second capacitors are coupled in series between the first port and the fourth port, with a first intermediate node between the first and second capacitors;

the third and fourth capacitors are coupled in series between the second port and the third port, with a second intermediate node between the third and fourth capacitors;

the first inductor is coupled between the first port and the second port;

the second inductor is coupled between the first intermediate node and the second intermediate node; and

the third inductor is coupled between the fourth port and the third port.

2. The quadrature hybrid of claim 1 , wherein the first variable capacitor tuning network includes a first plurality of capacitors and switches to provide a first tunable capacitance, and the second variable capacitor tuning network includes a second plurality of capacitors and switches to provide a second tunable capacitance.

3. The quadrature hybrid of claim 1 , wherein the first variable capacitor tuning network includes a first non-linear reactance component, and the second variable capacitor tuning network includes a second non-linear reactance component.

4. The quadrature hybrid of claim 3 , wherein the first non-linear reactance component is controlled with a first bias voltage, and the second non-linear reactance component is controlled with a second bias voltage.

5. The quadrature hybrid of claim 1 , wherein the first variable capacitor tuning network includes a first capacitor and a first switch, and the second variable capacitor tuning network includes a second capacitor and a second switch.

6. The quadrature hybrid of claim 5 , wherein at least one of the first capacitor and the first switch, and the second capacitor and the second switch are connected in parallel.

7. The quadrature hybrid of claim 5 , wherein at least one of the first capacitor and the first switch, and the second capacitor and the second switch are connected in series.

8. The quadrature hybrid of claim 1 , wherein the first variable capacitor tuning network includes a first capacitor and a first switch, and the second variable capacitor tuning network includes a second capacitor and a second switch; and

wherein the first capacitor and the first switch are connected in at least one in series and in parallel, and the second capacitor and the second switch are connected in at least one of in series and in parallel.

9. The quadrature hybrid of claim 1 , wherein the first variable capacitor tuning network and the second variable capacitor tuning network have a symmetric arrangement of capacitors and switches.

10. The quadrature hybrid of claim 1 , wherein the first variable capacitor tuning network and the second variable capacitor tuning network have an asymmetric arrangement of capacitors and switches.

11. The quadrature hybrid of claim 1 , wherein the first variable capacitor tuning network and the second variable capacitor tuning network tune a coupling factor of the quadrature hybrid.

12. An integrated circuit (IC) comprising:

a quadrature hybrid including:

a first port;

a second port;

a third port;

a fourth port;

first, second, and third inductors;

first, second, third, and fourth capacitors; and

a first variable capacitor tuning network connected between the first port and the fourth port; and

a second variable capacitor tuning network connected between the second port and the third port;

a quad hybrid controller that controls states of the first variable capacitor tuning network and the second variable capacitor tuning network;

a digital interface coupled to the quad hybrid controller; and

wherein:

the first and second capacitors are coupled in series between the first port and the fourth port, with a first intermediate node between the first and second capacitors;

the third and fourth capacitors are coupled in series between the second port and the third port, with a second intermediate node between the third and fourth capacitors;

the first inductor is coupled between the first port and the second port;

the second inductor is coupled between the first intermediate node and the second intermediate node; and

the third inductor is coupled between the fourth port and the third port.

13. The IC of claim 12 , wherein the first variable capacitor tuning network includes a first capacitor and a first switch, and the second variable capacitor tuning network includes a second capacitor and a second switch.

14. The IC of claim 12 , wherein the first variable capacitor tuning network includes a first non-linear reactance component, and the second variable capacitor tuning network includes a second non-linear reactance component.

15. A method of operating a quadrature hybrid, the method comprising:

controlling a capacitance value of a first variable capacitor tuning network, which includes a first capacitor, to tune a coupling factor of the quadrature hybrid; and

controlling a capacitance value of a second variable capacitor tuning network, which includes a second capacitor, to tune the coupling factor of the quadrature hybrid;

wherein:

the first variable capacitor tuning network includes a first switch connected in a configuration selected from the group consisting of parallel and series with the first capacitor, and controlling the capacitance value of the first variable capacitor tuning network comprises controlling the first switch; and

the second variable capacitor tuning network includes a second switch connected in a configuration selected from the group consisting of parallel and series with the second capacitor, and controlling the capacitance value of the second variable capacitor tuning network comprises controlling the second switch.

16. The method of claim 15 , wherein:

the first variable capacitor tuning network includes a first non-linear reactance component with a first variable capacitance value that is controlled with a first bias voltage, and controlling the first variable capacitance value of the first non-linear reactance component comprises providing the first bias voltage; and

the second variable capacitor tuning network includes a second non-linear reactance component with a second variable capacitance value that is controlled with a second bias voltage, and controlling the second variable capacitance value of the second non-linear reactance component comprises providing the second bias voltage.