Patent ID: 7482785

Claim:
A transponder device with an LC oscillator circuit, an energy storage capacitor and an integrated transponder circuit powered by energy from the storage capacitor, the device being adapted to operate either in a charge mode in which RF energy is received through the LC oscillator circuit and stored in the energy storage capacitor, or in a transmit mode in which data from the transponder circuit are transmitted from the transponder device through the LC oscillator circuit by sustaining oscillation of the LC oscillation circuit and selectively modulating the oscillator frequency; comprising: a stimulating circuit feeding energy from the storage capacitor into the LC oscillator circuit during the transmit mode to sustain oscillation thereof; a peak detector for detecting a peak voltage level of an RF oscillator signal in the LC oscillator circuit; a pulse generator for providing trigger pulses to the stimulating circuit in response to an output from the peak detector; and a control circuit for controlling the stimulating circuit to prevent the amplitude of the oscillator signal in the LC oscillator circuit from exceeding a predetermined peak value.