Antenna Driver Circuit for NFC Reader Applications

• US 20130084799A1
• Filed: 09/29/2011
• Published: 04/04/2013
• Est. Priority Date: 09/29/2011
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: SAFARIAN, Aminghasem, MARHOLEV, Bojko
• Granted Patent: US 8,929,808 B2
• Time in Patent Office: Days
• US Class Current: 455/41.1
• CPC Class Codes: H03F 2200/411 the output amplifying stage of an amplifier comprising two power stages
• CPC Class Codes: H03F 2203/45421 the CMCL comprising a switched capacitor addition circuit
• CPC Class Codes: H03F 2203/45424 the CMCL comprising a comparator circuit
• CPC Class Codes: H03F 3/245 with semiconductor devices only
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence
• CPC Class Codes: H03F 3/45641 Measuring at the loading circuit of the differential amplifier
• CPC Class Codes: H04B 5/24 Inductive coupling

Abstract

A power amplifier, supplied by a supply voltage, to drive an antenna to output a magnetic field, comprising a differential stage configured to output an output signal to drive the antenna, and a feedback stage configured to receive a common mode output voltage from the differential stage and to output a feedback voltage to regulate the output common mode signal to be proportional to the supply

Claims

1. A power amplifier, supplied by a supply voltage, to drive an antenna to output a magnetic field, comprising:

a differential stage configured to output an output signal to drive the antenna; and

a feedback stage configured to receive a common mode output voltage from the differential stage, and to output a feedback voltage to regulate the output signal to be proportional to the supply voltage.

2. The power amplifier of claim 1, wherein the differential stage comprises:

a positive stage configured to output a positive signal of the output signal to drive the antenna during a positive half cycle of an input signal; and

a negative stage configured to output a negative signal of the output signal to drive the antenna during a negative half cycle of the input signal.

3. The power amplifier of claim 2, wherein the common mode output voltage is derived from the positive signal and the negative signal.

4. The power amplifier of claim 1, wherein

the feedback stage is configured to compare the common mode output voltage and a reference voltage generated based on the supply voltage to output the feedback voltage, and

the differential stage is configured to modulate the output signal in accordance with the feedback voltage.

5. The power amplifier of claim 1, wherein an amplitude of the output signal changes in accordance with changes to the supply voltage.

6. The power amplifier of claim 2, wherein the output signal is centered at the reference voltage to allow the positive signal to swing between the reference voltage and a maximum supply voltage, and to allow the negative signal to swing between the reference voltage and a minimum supply voltage.

7. The power amplifier of claim 1, where the different stage and the feedback stage include laterally diffused metal oxide semiconductor (LDMOS) devices.

8. A near field communication (NFC) device comprising:

an antenna configured to output a magnetic field to establish communication with another device; and

a power amplifier, supplied by a supply voltage, to drive the antenna to output the magnetic field, the power amplifier including,

a differential stage configured to output an output signal to drive the antenna; and

a feedback stage configured to receive a common mode output voltage from the differential stage, and to output a feedback voltage to regulate the output common mode signal to be proportional to the supply voltage.

9. The near field communication (NFC) device of claim 8, wherein the differential stage comprises:

a positive stage configured to output a positive signal of the Output signal to drive the antenna during a positive half cycle of an input signal; and

a negative stage configured to output a negative signal of the output signal to drive the antenna during a negative half cycle of the input signal,

10. The near field communication (NFC) device of claim 9, wherein the common mode output voltage is derived from the positive signal and the negative signal.

11. The near field communication (NFC) device of claim 8, wherein

the feedback stage is configured to compare the common mode output voltage and a reference voltage generated based on the supply voltage to output the feedback voltage, and

the differential stage is configured to modulate the output signal in accordance with the feedback voltage.

12. The near field communication (NFC) device of claim 8, wherein an amplitude of the output signal changes in accordance with changes to the supply voltage.

13. The near field communication (NFC) device of claim 9, wherein the output signal is centered at the reference voltage to allow the positive signal to swing between the reference voltage and a maximum supply voltage, and to allow the negative signal to swing between the reference voltage and a minimum supply voltage.

14. The near field communication (NFC) device of claim 8, wherein the supply voltage is supplied by a battery powering the NFC device.

15. The near field communication device of claim 8, wherein the pseudo-different stage and the feedback stage include laterally diffused metal oxide semiconductor (LDMOS) devices.

16. A power amplifier, supplied by a supply voltage, to drive an antenna to output a magnetic field, comprising:

means for outputting an output signal to drive the antenna; and

means for receiving a common mode output voltage from the means for outputting, and to output a feedback voltage to regulate the output signal to be proportional to the supply voltage.

17. The power amplifier of claim 16, wherein the means for outputting comprises:

means for outputting a positive signal of the output signal to drive the antenna during a positive half cycle of an input signal; and

means for outputting a negative signal of the output signal to drive the antenna during a negative half cycle of the input signal.

18. The power amplifier of claim 17, wherein the common mode output voltage is derived from the positive signal and the negative signal.

19. The power amplifier of claim 16, wherein

the means for receiving compares the common mode output voltage and a reference voltage generated based on the supply voltage to output the feedback voltage, and

the means for outputting modulates the output signal in accordance with the feedback voltage.

20. The power amplifier of claim 16, wherein an amplitude of the output signal changes in accordance with changes to the supply voltage.