Near-field communications low-power presence check

A method, comprising:

• detecting a presence of a tag by at least:
• causing an antenna to generate a magnetic field over a first time period for detecting the tag;
• measuring an antenna voltage over a second time period;
• causing the antenna to cease generating a magnetic field over a third time period longer than the first time period;
• and
• comparing the antenna voltage to an antenna reference voltage to determine whether the tag is present.

A controller, comprising:

• an input coupled to an antenna matching element that is coupled to an antenna;
• and
• an output coupled to the antenna matching, wherein the controller is configured to:
• detect presence of a tag by at least:
• causing the antenna to generate a magnetic field over a first time period for detecting the tag;
• measuring an antenna voltage over a second time period;
• causing the antenna to cease generating a magnetic field over a third time period longer than the first time period;
• and
• comparing the antenna voltage to an antenna reference voltage to determine whether the tag is present.