Gain invariant bidirectional phase shifter

1 . An apparatus comprising:

a coupler including a first port, a second port, and a third port, in which the second port and the third port have a 90-degree phase shift from each other:

a phase shifter having a phase control terminal and a variable resistance circuit coupled to the phase control terminal; and

a switch network coupled between the second and third ports and the phase shifter.

2 . The apparatus of claim 1 , wherein the coupler is a first hybrid coupler, and the phase shifter includes:

a second hybrid coupler having a first port;

a resonator circuit coupled to the first port of the second hybrid coupler; and

the variable resistance circuit coupled to the resonator circuit.

3 . The apparatus of claim 2 , wherein the resonator circuit has a phase control terminal, and the variable resistance circuit includes:

a first transistor including:

a source coupled to a power supply terminal;

a gate coupled to the phase control terminal of the resonator circuit; and

a drain coupled to a port of the second hybrid coupler; and

a second transistor including:

a source coupled to a reference voltage terminal;

a gate coupled to the phase control terminal of the resonator circuit; and

a drain coupled to the port of the second hybrid coupler.

4 . The apparatus of claim 2 , wherein the resonator circuit has a terminal coupled to the phase control terminal, and the variable resistance circuit includes:

a first transistor including:

a source coupled to a power supply terminal;

a gate coupled to the phase control terminal of the resonator circuit; and

a drain coupled to a port of the second hybrid coupler; and

a resistor including:

a first terminal coupled to a reference voltage terminal; and

a second terminal coupled to the port of the second hybrid coupler.

5 . The apparatus of claim 2 , wherein:

the second hybrid coupler includes a second port;

the resonator circuit is a first resonator circuit;

the variable resistance circuit is a first variable resistance circuit; and

the phase shifter includes:

a second resonator circuit coupled to the second port of the second hybrid coupler; and

a second variable resistance circuit coupled to the second resonator circuit.

6 . The apparatus of claim 5 , wherein the first resonator circuit includes a first capacitor having a first adjustable capacitance, the first capacitor has a first capacitance control terminal coupled to the phase control terminal; and

wherein the second resonator circuit includes a second capacitor having a second adjustable capacitance, the second capacitor has a second capacitance control terminal coupled to the phase control terminal.

7 . The apparatus of claim 5 , further comprising a first capacitor coupled between the first resonator circuit and the first port of the second hybrid coupler, and a second capacitor coupled between the second resonator circuit and the second port of the second hybrid coupler.

8 . The apparatus of claim 5 , wherein the second hybrid coupler has a third port and a fourth port having a 90-degree phase shift from each other; and

wherein the phase shifter has differential terminals coupled to the third and fourth ports of the second hybrid coupler.

9 . The apparatus of claim 1 , wherein:

the coupler is a differential quadrature hybrid coupler;

the first port includes first differential terminals;

the second port includes second differential terminals;

the third port includes third differential terminals; and

the phase shifter includes a differential phase shifter having fourth differential terminals coupled to the switch network.

10 . The apparatus of claim 9 , wherein the switch network includes:

a first switch coupled between a first terminal of the second differential terminals and a first terminal of the fourth differential terminals;

a second switch coupled between the first terminal of the second differential terminals and a second terminal of the fourth differential terminals;

a third switch coupled between a second terminal of the second differential terminals and the first terminal of the fourth differential terminals; and

a fourth switch coupled between the second terminal of the second differential terminals and the second terminal of the fourth differential terminals.

11 . The apparatus of claim 10 , wherein the switch network includes:

a fifth switch coupled between a first terminal of the third differential terminals and the first terminal of the fourth differential terminals;

a sixth switch coupled between the first terminal of the third differential terminals and the second terminal of the fourth differential terminals;

a seventh switch coupled between a second terminal of the third differential terminals and the first terminal of the fourth differential terminals; and

an eighth switch coupled between the second terminal of the third differential terminals and the second terminal of the fourth differential terminals.

12 . The apparatus of claim 1 , wherein the phase shifter includes a reflection type phase shifter.

13 . The apparatus of claim 1 , wherein the coupler, the switch network, and the phase shifter are part of a bidirectional phase shifter.

14 . The apparatus of claim 1 , wherein the coupler, the switch network, and the phase shifter are part of a beamforming circuit.

15 . The apparatus of claim 1 , wherein the phase shifter includes at least two bidirectional input/output (I/O) ports.

16 . The apparatus of claim 1 , wherein the phase shifter includes two differential bidirectional input/output (I/O) ports.