Three-port shunted inductor lattice coupler

1. A coupler having first, second, and third ports, and comprising:

a first inductor coupled between the first port and a first grounding node;

a second inductor coupled between the second port and a second grounding node, wherein the first inductor and the second inductor have a predetermined mutual magnetic coupling factor;

a third inductor coupled between the first port and the third port;

a first capacitor coupled between the first port and a third grounding node;

a second capacitor coupled between the second port and the third port; and

one or more third capacitors coupled between the first grounding node and circuit ground and between the second grounding node and circuit ground.

2. The coupler of claim 1 , wherein the first and second inductors have equal values of inductance to within a 20% tolerance.

3. The coupler of claim 1 , wherein the predetermined mutual magnetic coupling factor is less than 0.1.

4. The coupler of claim 1 , wherein the predetermined mutual magnetic coupling factor is at least 0.2.

5. An amplifier assembly comprising:

a differential amplifier having first and second out-of-phase signal inputs; and

the coupler of claim 1 ;

wherein the first and second ports of the coupler are respectively coupled to the first and second out-of-phase signal inputs of the differential amplifier.

6. The coupler of claim 1 , wherein the coupler provides a DC block between the second port and circuit ground.

7. The coupler of claim 1 , wherein the predetermined mutual magnetic coupling factor is at least 0.6.

8. The coupler of claim 1 , wherein the first and second inductors comprise respective first and second planar spiral patterns formed on a substrate.

9. The coupler of claim 1 , wherein a coupling imbalance between the first and second ports varies by less than 0.5 dB over a 10% bandwidth.

10. A system comprising:

a differential amplifier having first and second out-of-phase signal outputs;

the coupler of claim 1 ; and

an antenna coupled to the third port of the coupler;

wherein the first and second ports of the coupler are respectively coupled to the first and second out-of-phase signal outputs.

11. The coupler of claim 1 , wherein:

the coupler is a three-port combiner configured to:

receive differential input signals at the first and second ports;

provide a single-ended output signal at the third port;

propagate a first bias voltage applied at the first grounding node to the first port; and

propagate a second bias voltage applied at the second grounding node to the second port; and

resistive losses of the coupler are due to non-ideal components.

12. The coupler of claim 11 , wherein:

the differential input signals are balanced;

the second grounding node is the first grounding node;

the second bias voltage is the first bias voltage; and

the first and second inductors have equal values of inductance to within a 20% tolerance.

13. A coupler having first, second, and third ports, and comprising:

a first inductor coupled between the first port and a first grounding node;

a second inductor coupled between the second port and a second grounding node, wherein the first inductor and the second inductor have a predetermined mutual magnetic coupling factor;

a third inductor coupled between the first port and the third port;

a first capacitor coupled between the first port and a third grounding node; and

a second capacitor coupled between the second port and the third port;

wherein the coupler is configured to receive out-of-phase first and second input signals at the first and second ports respectively, and to generate a combined output signal at the third port; and

wherein the input impedance at each of the first and second ports varies by less than 15% over a 10% bandwidth.

14. The coupler of claim 13 , wherein:

the coupler is configured to receive an input signal at the third port and to generate out-of-phase first and second output signals at the first and second ports respectively; and

a phase difference between the first and second output signals varies by less than 5° over a 10% bandwidth.

15. The coupler of claim 13 , wherein:

the out-of-phase first and second input signals are differential input signals;

the coupler is a three-port combiner; and

resistive losses of the coupler are due to non-ideal components.

16. The coupler of claim 15 , wherein:

the differential input signals are balanced;

the second grounding node is the first grounding node;

the coupler further comprises one or more third capacitors coupled between the first grounding node and circuit ground;

the coupler is configured to propagate a bias voltage applied at the first grounding node to the first port and to the second port; and

the first and second inductors have equal values of inductance to within a 20% tolerance.

17. A system comprising:

a differential amplifier having first and second out-of-phase signal outputs; and

an antenna;

a bias power supply;

a circuit ground; and

a combiner comprising:

first and second ports respectively coupled to the first and second out-of-phase signal outputs of the differential amplifier;

a third port coupled to the antenna;

a terminal coupled to the bias power supply;

a first inductor coupled between the first port and the terminal;

a second inductor coupled between the second port and the terminal, wherein the first inductor and the second inductor have a mutual magnetic coupling factor of at least 0.2;

a third inductor coupled between the first port and the third port;

a first capacitor coupled between the first port and the circuit ground;

a second capacitor coupled between the second port and the third port; and

a third capacitor coupled between the terminal and the circuit ground.

18. The system of claim 17 , wherein the differential amplifier has first and second out-of-phase signal inputs, and further comprising:

a signal source; and

a splitter comprising:

fifth and sixth ports respectively coupled to the first and second signal out-of-phase inputs of the differential amplifier;

a seventh port coupled to receive an input signal from the signal source;

a fourth inductor coupled between the fifth port and a grounding node;

a fifth inductor coupled between the sixth port and the grounding node, wherein the fourth inductor and the fifth inductor have a mutual magnetic coupling factor of at least 0.2;

a sixth inductor coupled between the fifth port and the seventh port;

a fourth capacitor coupled between the fifth port and the circuit ground; and

a fifth capacitor coupled between the sixth port and the seventh port.

19. The system of claim 17 , wherein the system is a cell phone.

20. A method comprising:

receiving a first signal outputted from a first RF amplifier at a first port of a combiner;

receiving a second signal outputted by a second RF amplifier at a second port of the combiner, wherein the first and second output signals are out-of-phase;

distributing the first signal from the first port along first, second, and third paths, wherein:

the first path passes through a first inductive component to a first grounding node;

the second path passes through a first capacitive component to a second grounding node; and

the third path passes through a second inductive component to a third port of the combiner;

distributing the second signal from the second port along fourth and fifth paths, wherein:

the fourth path passes through a third inductive component to a third grounding node, wherein the first and third inductive components have a mutual magnetic coupling factor of at least 0.2; and

the fifth path passes through a second capacitive component to the third port of the combiner; and

at the third port, responsive to receiving a portion of the first signal along the third path and receiving a portion of the second signal along the fifth path, outputting a third signal from the combiner.

21. The method of claim 20 , wherein the third signal is outputted toward an antenna.

22. The method of claim 20 , further comprising:

applying a bias voltage for the first RF amplifier at the first grounding node.

23. The method of claim 20 , wherein:

magnitudes of the first and second signals have a first predetermined ratio;

inductance values of the first and third inductive components have a second predetermined ratio; and

the second predetermined ratio is selected based on the first predetermined ratio and on the mutual magnetic coupling factor.