Patent ID: 7515881

Claim:
A communication system, comprising: an antenna with a resonant circuit, the resonant circuit including an inductive coil connected to a tuning capacitor; means to selectively drive the resonant circuit during a transmit mode; means to selectively receive an induced signal in the resonant circuit during a receive mode; and means to selectively include a frequency shift canceling component in the resonant circuit to provide a first resonance frequency in the resonant circuit in the transmit mode and a second resonance frequency in the resonant circuit in the receive mode such that the first resonance frequency and the second resonance frequency are approximately equal, wherein the means to selectively include a frequency shift canceling component in the resonant circuit includes means to selectively exclude a predetermined parallel capacitance with respect to the tuning capacitor when switching from the receive mode to the transmit mode, and to selectively include the predetermined parallel capacitance with respect to the tuning capacitor when switching from the transmit mode to the receive mode.