NFC device combining components of antenna driver and shunt regulator

1. A circuit comprising:

an antenna port coupled to a first transistor, a second transistor, and a third transistor;

a predriver;

a first switch configured to couple the predriver to the first transistor;

a second switch configured to couple the predriver to the second transistor;

a third switch configured to couple the predriver to the third transistor;

a voltage regulator;

a fourth switch configured to couple the voltage regulator to the second transistor;

a clamp control; and

a fifth switch configured to couple the clamp control to the third transistor,

wherein:

during a first mode, the first switch, the second switch, and the third switch are configured to close while the fourth switch and the fifth switch are configured to open, and

during a second mode, the first switch, the second switch, and the third switch are configured to open while the fourth switch and the fifth switch are configured to close.

2. The circuit of claim 1 , wherein the first transistor is a P-type metal-oxide-semiconductor (PMOS) transistor, and wherein the second and third transistors are N-type metal-oxide-semiconductor (NMOS) transistors.

3. The circuit of claim 1 , wherein the antenna port is an antenna port of a near field communications (NFC) device, wherein the antenna port is configured to support a reader mode of the NFC device during the first mode, and wherein the antenna port is configured to support a target mode of the NFC device during the second mode.

4. The circuit of claim 1 , further comprising a diode coupled to the antenna port and the voltage regulator, wherein the voltage regulator is configured to:

receive a feedback signal from the diode;

compare the feedback signal to a reference signal; and

adjust a voltage supplied to the second transistor in response to the comparison between the feedback signal and the reference signal.

5. The circuit of claim 1 , further comprising:

a second antenna port coupled to a fourth transistor, a fifth transistor, and a sixth transistor, wherein:

the predriver is further configured to be coupled to the fourth transistor, the fifth transistor, and the sixth transistor,

the voltage regulator is further configured to be coupled to the fifth transistor, and

the clamp control is further configured to be coupled to the sixth transistor.

6. The circuit of claim 5 , wherein the clamp control is configured to:

determine whether a first voltage of the antenna port or a second voltage of the second antenna port is lower;

create a short circuit at first antenna port if the first voltage is lower; and

create a short circuit at the second antenna port if the second voltage is lower.

7. The circuit of claim 1 , wherein the fourth switch is configured to couple the voltage regulator to the second transistor such that the voltage regulator and the predriver are not both coupled to the second transistor at the same time.

8. The circuit of claim 1 , wherein the fifth switch is configured to couple the clamp control to the third transistor such that the clamp control and the predriver are not both coupled to the third transistor at the same time.

9. The circuit of claim 1 , wherein the fourth switch is configured to couple the voltage regulator to a gate of the second transistor, and wherein the fifth switch is configured to couple the clamp control to a gate of the third transistor.

10. The circuit of claim 1 , wherein the voltage regulator is configured to maintain a signal supplied to the antenna port at a stable voltage without requiring a coupling of the voltage regulator to any additional transistor.

11. The circuit of claim 1 , wherein the clamp control is configured to prevent a voltage at the antenna port from exceeding a predefined magnitude without requiring a coupling of the clamp control to any additional transistor.

12. The circuit of claim 1 , further comprising: a sixth switch configured to couple the first switch to the antenna.

13. A near field communications (NFC) device comprising:

a first antenna port coupled to a first plurality of transistors including a first transistor, a second transistor, and a third transistor;

a second antenna port coupled to a second plurality of transistors;

a predriver configured to be coupled to the first plurality of transistors and the second plurality of transistors;

a first switch configured to couple the predriver to the first transistor;

a second switch configured to couple the predriver to the second transistor;

a third switch configured to couple the predriver to the third transistor;

a voltage regulator configured to be coupled to the first antenna port and the second antenna port;

a fourth switch configured to couple the voltage regulator to the second transistor;

a clamp control configured to be coupled to the first antenna port and the second antenna port; and

a fifth switch configured to couple the clamp control to the third transistor, wherein:

during a first mode, the first switch, the second switch, and the third switch are configured to close while the fourth switch and the fifth switch are configured to open, and

during a second mode, the first switch, the second switch, and the third switch are configured to open while the fourth switch and the fifth switch are configured to close.

14. The NFC device of claim 13 , wherein the NFC device is configured to receive information instructing the NFC device to place the first antenna port in the first mode or the second mode, wherein the first mode is a reader mode, and wherein the second mode is a target mode.

15. The NFC device of claim 13 , wherein the fourth switch is configured to couple the voltage regulator to the second transistor such that the voltage regulator and the predriver are not both coupled to the second transistor at the same time.

16. The NFC device of claim 13 , wherein the fifth switch is configured to couple the clamp control to the third transistor such that the clamp control and the predriver are not both coupled to the third transistor at the same time.

17. The NFC device of claim 13 , further comprising: a sixth switch configured to couple the first switch to the first antenna port.

18. A method comprising:

determining whether an antenna port is used to receive a magnetic field or to create the magnetic field; and

in response to determining that the antenna port is used to create the magnetic field:

coupling, via a first switch, a predriver to a first transistor,

coupling, via a second switch, the predriver to a second transistor,

coupling, via a third switch, the predriver to a third transistor,

decoupling, via a fourth switch, a voltage regulator from the second transistor, and

decoupling, via a fifth switch, a clamp control from the third transistor, wherein, if the antenna port is configured to receive the magnetic field, the first switch, the second switch, and the third switch are open while the fourth switch and the fifth switch are closed.

19. The method of claim 18 , further comprising:

in response to determining that the antenna port is used to receive the magnetic field:

decoupling, via the first switch, the predriver from the first transistor,

decoupling, via the second switch, the predriver from the second transistor,

decoupling, via the third switch, the predriver from the third transistor,

coupling, via the fourth switch, the regulator to the second transistor, and

coupling, via the fifth switch, the clamp control to the third transistor.

20. The method of claim 18 , further comprising determining whether the antenna port is used to receive the magnetic field or to create the magnetic field based on instructions received from a host near field communications (NFC) device.