A method of processing a signal of a passive RFID chip with a reader, the reader comprising an antenna, an operational amplifier, an AD converter and a first DA converter and further a second DA converter or a source of constant voltage, the method consisting of steps of transmitting a source signal from the antenna, and receiving a RFID chip signal by the antenna, characterized in that - the received RFID chip signal and the output of the first DA converter are fed to an inverting input of the operational amplifier, - the output of the second DA converter or the output of the source of constant voltage is fed to a non-inverting input of the operational amplifier, - a first pair of values for controlling the first and the second DA converter or the source of constant voltage is chosen, wherein this pair of values is chosen so that the window of the operational amplifier scans the positive half wave of the received RFID chip signal, - a second pair of values for controlling the first and the second DA converter or the source of constant voltage is chosen, wherein this pair of values is chosen so that the window of the operational amplifier scans the negative half wave of the received RFID chip signal, - an output signal from the operational amplifier is fed to the AD converter, -, and by continuously and alternately processing the positive and negative half waves of the received RFID signal by the AD converter to obtain pulse signals and - subtracting the pulse signals corresponding to the positive and negative half waves from the same wave to obtain a digitally processed signal. the antenna, and receiving a RFID chip signal by the antenna, characterized in that - the received RFID chip signal and the output of the first DA converter are fed to an inverting input of the operational amplifier, - the output of the second DA converter or the output of the source of constant voltage is fed to a non-inverting input of the operational amplifier, - a first pair of values for controlling the first and the second DA converter or the source of constant voltage is chosen, wherein this pair of values is chosen so that the window of the operational amplifier scans the positive half wave of the received RFID chip signal, - a second pair of values for controlling the first and the second DA converter or the source of constant voltage is chosen, wherein this pair of values is chosen so that the window of the operational amplifier scans the negative half wave of the received RFID chip signal, - an output signal from the operational amplifier is fed to the AD converter, -, and by continuously and alternately processing the positive and negative half waves of the received RFID signal by the AD converter to obtain pulse signals and - subtracting the pulse signals corresponding to the positive and negative half waves from the same wave to obtain a digitally processed signal. - the received RFID chip signal and the output of the first DA converter are fed to an inverting input of the operational amplifier, - the output of the second DA converter or the output of the source of constant voltage is fed to a non-inverting input of the operational amplifier, - a first pair of values for controlling the first and the second DA converter or the source of constant voltage is chosen, wherein this pair of values is chosen so that the window of the operational amplifier scans the positive half wave of the received RFID chip signal, - a second pair of values for controlling the first and the second DA converter or the source of constant voltage is chosen, wherein this pair of values is chosen so that the window of the operational amplifier scans the negative half wave of the received RFID chip signal, - an output signal from the operational amplifier is fed to the AD converter, -, and by continuously and alternately processing the positive and negative half waves of the received RFID signal by the AD converter to obtain pulse signals and - subtracting the pulse signals corresponding to the positive and negative half waves from the same wave to obtain a digitally processed signal.