Patent ID: 8243049

Claim:
An untethered stylus configured to cooperate with a location sensor, the location sensor configured to generate a varying magnetic field and communicatively couple to the stylus, the stylus comprising: a housing configured for hand-held manipulation; a coil resonant circuit provided in the housing and configured to develop an arbitrary AC voltage in response to the magnetic field, the coil resonant circuit comprising a first capacitor and an inductive coil; and a power converter coupled to the coil resonant circuit and comprising a switch circuit and a second capacitor, the switch circuit having an output coupled to the second capacitor, an input coupled to the coil resonant circuit, and a threshold voltage, the switch circuit configured to facilitate charging of the second capacitor in response to the arbitrary AC voltage by transferring charge from the first capacitor to the second capacitor through the switch circuit, the switch circuit also being configured to discontinue both charging of the second capacitor and discharging of the first capacitor in response to a voltage across the second capacitor reaching the threshold voltage, wherein a stable DC voltage is provided at the output of the switch circuit; wherein the power converter powers a circuit of the stylus using power derived from the magnetic field rather than power derived from a battery; and wherein the switch circuit comprises a depletion FET having a gate-source voltage, V gs , as the threshold voltage.