Patent ID: 7689195

Claim:
A passive radio frequency identification (RFID) transponder receiver that is powered by an induced magnetic field comprising: a first detector to remove a carrier and extract an envelope of a received RFID signal; a second detector includes a sample and hold circuit and a comparator, coupled to receive the extracted envelope of the received RFID signal, wherein the sample and hold circuit outputs a previous extracted envelope sample of the received RFID signal to an input of the comparator and the comparator compares a sample of the extracted envelope with the previous extracted envelope sample of the received RFID signal to generate an output in response to the comparison, in which the second detector samples a pulse of one polarity and inhibits sampling of a pulse of opposite polarity when operating in a pulse detection mode and detects level change of the extracted envelope when operating in a level detection mode; a clock extractor to extract a clock signal from the received RFID signal; a digital decoder coupled to the second detector and to the clock extractor to use the extracted clock signal from the clock extractor to generate a divided clock signal of reduced duty cycle from the extracted clock signal to clock the sample and hold circuit and in which the digital decoder determines when the extracted envelope meets a minimum threshold level in order for the output to be valid; and an automatic gain control (AGC) circuit coupled to the first detector and the digital decoder to control a gain of an input attenuator circuit of the receiver to control input signal level of the received RFID signal to reside between an upper threshold level and a lower threshold level.