Method and driver circuit for resonant antenna circuit

A method of driving a resonant antenna circuit for generating an oscillating voltage signal at a predefined target frequency, the resonant antenna circuit comprising three branches connected in parallel, including:

• a first branch comprising an inductor coil;
• a second branch comprising a first capacitance;
• a third branch comprising a second capacitance connected in series with a first switch;
• and wherein the first capacitance is chosen such that the antenna circuit has a first resonance frequency higher than the target frequency if the first switch would be permanently open;
• wherein the second capacitance is chosen such that the antenna circuit has a second resonance frequency lower than the target frequency if the first switch would be permanently closed;
• the method comprises the steps of:
• a) monitoring the oscillating voltage signal of the resonant antenna circuit;
• b) detecting oscillations of said oscillating voltage signal by detecting zero-crossing-moments defined as moments in time at which the oscillating voltage crosses a fixed or variable DC level;
• c) dynamically controlling the first switch by selectively opening and closing the first switch at said zero-crossing moments and keeping the first switch open or closed between said zero-crossing moments, so that, on average, the number of oscillations of the oscillating voltage per time unit is substantially equal to the target frequency.