Transponder system and method

A method is provided for operating an RF transponder system to detect the presence of an RFID device in the proximal space of an RF reader unit. The RF reader unit has an excitation signal generator circuit, an RFID device detection circuit coupled to the excitation signal generator circuit, and a power source. The excitation signal generator circuit unit initially operates in a reduced power state effected by drawing reduced electrical current from the power source. The excitation signal generator circuit generates ring signals in response to the reduced electrical current and transmits the ring signals into the proximal space. The RFID device detection circuit evaluates the ring signals to determine variations in an RFID device detection parameter of the ring signals. When the variation in the RFID device detection parameter passes a variation threshold level due to the presence of the RFID device in the proximal space, the excitation signal generator circuit switches from the reduced power state to an increased power state and generation of the ring signals is terminated. The excitation signal generator circuit draws increased electrical current from the power source in the increased power state to generate an RF excitation signal which is transmitted to the RFID device, having a transponder circuit powered by the RF excitation signal. The transponder circuit processes the RF excitation signal, generates an RF response signal, and transmits the RF response signal to an ER circuit housed in the RF reader unit. The ER circuit reads the RF response signal and the excitation signal generator circuit switches back to the reduced power state, resuming generation of the ring signals while terminating generation of the RF excitation signal.