Near field communication reader with variable power supply

A near field communications (NFC) reader comprising:

• a series resonant circuit including an antenna;
• an amplifier configured to drive the antenna;
• a first variable capacitance connected in series between a first differential output of the amplifier and a first terminal of the antenna;
• a second variable capacitance connected in series between a second differential output of the amplifier and a second terminal of the antenna, the first and second variable capacitances configured to tune the resonant circuit to a desired resonant frequency to compensate for a change in an impedance of the antenna resulting from a change in coupling between the antenna and an antenna of a tag with which the NFC reader is communicating;
• a power supply including an output coupled to a power supply input of the amplifier, and
• a control circuit configured to control a voltage supplied by the power supply to the power supply input of the amplifier.