Data detector for UHF RFID tags
A method of detecting a signal in radio frequency identification (RFID) transponder (FIG. 1 ) is disclosed. The method includes receiving a signal (FIG. 7 ) having a first time in a first logic state (high) and having a second time in a second logic state (low). A weight ( 700, 702 ) is determined in response to the first time and the second time. An output signal (from A2D) is produced in response to the weight and one of the first and second logic states.
1. In an RFID circuit for receiving a modulated RF signal having an envelope corresponding to digital coding of information, a method of detecting the signal, comprising:
receiving a signal having a signal strength dependent on distance from an interrogator including a preamble and having a first time in a first logic state and having a second time in a second logic state;
dynamically determining a weighted average voltage from the preamble in response to the first time and the second time, the weighted average voltage being between voltages representing the first logic state and the second logic state and being determined by the relative number of the first and second logic states in the preamble;
generating a voltage representative of the envelope;
controlling a value of the envelope voltage utilizing the weighted average voltage from the preamble to generate a value closer to or equal to an ideal comparison voltage; and
comparing the comparison voltage to the received signal to produce an output signal in response to one of the first and second logic states.
2. A method as in claim 1 , wherein the step of receiving comprises:
receiving a pulse-interval encoded signal; and
rectifying the pulse-interval encoded signal.
3. A method as in claim 2 , wherein the step of receiving comprises limiting the signal after the step of rectifying.
4. A method as in claim 1 , wherein the step of determining comprises estimating a duty cycle of the signal.
5. A method as in claim 1 , wherein the step of determining comprises counting a number of clock cycles during each of the first and second times.
6. A method as in claim 1 , wherein the weight determines an input offset for a data comparator.
7. A method as in claim 1 , wherein the weight determines an input offset for a data slicer.
8. The method of claim 1 wherein the ideal comparison voltage is midway between the envelope signal levels.