A pulse-width modulation amplifier comprises a feedback loop for reshaping the pulses of the PWM input signal to correct timing and amplitude errors in the class D output stage of the amplifier by means of an error correction signal. The RFID tag has a metal holder, a housing that is made of an electrically non-conductive or slightly conductive material, an accommodating chamber and an RFID element with an antenna. A second digest representing a second data unit stored in a second memory different from the first memory, is generated.