Patent ID: 8896368

Claim:
A method of operating an electromagnetic transponder that includes an antenna circuit, a load, and a charge pump transistor having a current path coupled between the antenna circuit and the load, the method comprising: transmitting a retromodulated signal at a first level by biasing the charge pump transistor during a first time period such that an impedance of the antenna circuit has a first impedance value and current flows from the antenna circuit through the charge pump transistor to the load; and transmitting the retromodulated signal at a second level by biasing the charge pump transistor during a second time period such that the impedance of the antenna circuit has a second impedance value different than the first impedance value and current flows from the antenna circuit through the charge pump transistor to the load, wherein the retromodulated signals are transmitted at the first and second levels in a sequence determined to transmit information from the electromagnetic transponder.