Dual standard RF-ID system

Claim 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, and wherein said amplitude of said pulses is dependent upon said number of detected zero crossings.