×

Dual standard RF-ID system

  • US 5,451,958 A
  • Filed: 05/21/1993
  • Issued: 09/19/1995
  • Est. Priority Date: 05/21/1993
  • Status: Expired due to Term
First Claim
Patent Images

1. A dual standard RF-ID protocal system, which can receive and recognize FDX(FSK), HDX(FSK) and FDX(ASK) transponders comprising:

  • a first antenna circuit for transmitting an excitation pulse to charge-up HD transponders and immediately initiate the FD transponders to respond;

    a second antenna circuit for receiving a transponders RF frequency response signal;

    a mixer circuit which mixes the transponder RF frequency signal with one LO frequency signal and yields a predetermined IF frequency signal;

    an amplifier circuit for amplifying said IF frequency signal and comprising a signal-detect circuit which detects the presence or absence of an FDX(FSK) signal being received;

    an amplitude limiting circuit for amplitude limiting said IF frequency signal; and

    a demodulator circuit for demodulation of said IF frequency signal into a train of pulses having different amplitudes and constant width comprising;

    a zero detector circuit for detecting the number of zero crossings in a predetermined amount of time,a timer for defining said predetermined time for said zero detector circuit, andwherein said amplitude of said pulses is dependent upon said number of detected zero crossings.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×