Method for tuning an oscillating receiver circuit of a transponder built into a RFID system

A method for calibrating an oscillating receiver circuit of a transponder in a radial frequency identification system to resonance to the frequency of an inquiry signal transmitted by a reader, the oscillating receiver circuit comprising at least one capacitor, the method comprising the steps of:

• transmitting the inquiry signal from the reader to the oscillating receiver circuit;
• changing capacitance of the oscillating receiver circuit in increments by adding or subtracting capacitances, wherein the capacitances of the capacitor are graduated in binary-weighted form and the capacitors are triggered using a binary counter;
• and
• retaining counter state of the binary counter at the maximum voltage value in order to perform the calibration.

A method for calibrating a transponder to the resident frequency of a base station during an initialization phase, comprising the steps of:

• (a) providing an oscillating circuit;
• (b) rectifying and smoothing a first induced voltage induced in a coil;
• (c) storing said first induced voltage in memory;
• (d) connecting a capacitor in parallel to the oscillating circuits to increase the capacitance of the transponder;
• (e) storing a second induced voltage in memory based on the increased capacitance;
• (f) comparing the second induced voltage to the first induced voltage;
• (g) replacing the first induced voltage with the second induced voltage in memory;
• (h) adding a capacitor if the second induced voltage is greater than the first voltage;
• and
• (i) repeating steps (d)-(i) until the second voltage is less than the first voltage;
• and
• (j) recording the capacitance associated with the first voltage so that the transponder calibrates itself to the resident frequency of the base station.