Rf backscatter transmission with zero dc power consumption

Abstract

A method for minimizing power consumption in a wireless device which utilizes backscatter transmission in half-duplex mode, wherein a switching device is interposed between an antenna and a transmitter-receiver, and the switching device is capable of causing the antenna load impedance characteristic to be either a short, a value which substantially matches the antenna impedance, or an open, depending on the portion of the half-duplex mode.

1 . In an transmitter-receiver circuit capable of half-duplex communication wherein the transmitter-receiver is connected to an antenna, a method of minimizing power consumption comprising
 setting, during a listening stage of a half-duplex cycle, an antenna load impedance characteristic to match the impedance of the antenna,   varying, during a transmitting stage of a half-duplex cycle, the antenna load impedance characteristic between a short impedance characteristic and a matching impedance characteristic.   
     
     
         2 . The method of  claim 1  wherein the varying step comprises switching impedances into and out of the circuit to vary the impedance. 
     
     
         3 . The method of  claim 2  wherein the switching step involving applying a voltage to the gate of a FET. 
     
     
         4 . A transmitter-receiver circuit capable of half-duplex communication comprising
 an antenna having an impedance,   a half-duplex transmitter-receiver, and   switching logic connected between the antenna and the transmitter-receiver, the switching logic adapted to establish an antenna load impedance characteristic which matches the antenna impedance during a listening portion of a half-duplex cycle, and, during the transmit portion of the half-duplex cycle, to vary the antenna load impedance characteristic between a short and a match to the antenna impedance.   
     
     
         5 . A transmitter-receiver circuit capable of half-duplex communication comprising
 an antenna,   a transmitter-receiver capable of operating in half-duplex mode at a baseband having a phase and a magnitude, and   logic for varying the magnitude and the phase of the baseband as applied to the antenna.   
     
     
         6 . The transmitter-receiver circuit of  claim 5  further including switching logic connected between the antenna and the transmitter-receiver for varying the antenna load impedance characteristic in accordance with the portion of the half-duplex cycle.