Patent ID: 8306489

Claim:
A circuit comprising: an output amplifier configured to amplify a transmit signal, the output amplifier having an output connectable to a first antenna terminal of a loop antenna; and a tuning device for automatic tuning, the tuning device comprising: a terminal that is separated from the output of the output amplifier and that is connectable to a second antenna terminal of the loop antenna; an adjustable tuning impedance that is connectable to the second terminal; a measurement device that is connectable to the adjustable tuning impedance, the measurement device operable to measure a voltage amplitude across the adjustable tuning impedance, the measurement device operable to be switched off; and a computing unit that is connectable to the measurement device and the adjustable tuning impedance, the computing unit configured to: automatically adjust the adjustable tuning impedance based on an evaluation of the voltage amplitude and the adjustable tuning impedance; and switch off the measurement device during a transmit operation.