PROCEDURE AND CIRCUIT FOR REDUCING NOISE LEVELS IN THE RECEIVED SIGNAL WITHIN A CONTACTLESS CARD POLLING DEVICE

摘要

Inside the polling device a calibration signal by the transmitter is generated in such a way that the signal of the local oscillator is shallow-amplitude modulated by a pilot signal featuring a frequency by which the contactless card encodes data. A reference signal of the receiver by the polling device is generated considering that the calibrating signal by the transmitter is merged with the signal whose carrier signal features a frequency that is equal to the frequency of the local oscillator and which is then transferred to the band filter and is then amplified. The receiver's output signals are filtered so that the receiver's reference signal with calibrated polarity attenuated by the calibration factor is deducted from it. The attenuation factors of the reference signal as well as its polarity for both the receiver's output signals are calibrated so that for each of them the attenuation factors of the reference signal as well as its polarity are set and defined as a value pair, where the filtered receiving output signals feature the smallest amplitude. The output signal of the receiver by the card polling device features an improved signal-noise ratio since it does not include any amplitude noise by the transmitter of the card polling device.