Closed loop inverse load modulation power control by magnetic field diminishment in inductively powered biomedical implants

A combination of an on-chip power control and a closed loop power control for inductively powered biomedical implants using inherent inverse load modulation as back channel is presented. Inverse load modulation is realized using an innovative internal on-chip power control. By shorting the secondary receiving coil to ground using varying switching pulse repetition rates the magnetic field is diminished and the load is nearly canceled. This reduces the energy absorbed by the implant and consequently the transmitted power decreases with a slight increase of the voltage amplitude in the primary transmitting coil. The increased amplitude peaks on the transmitter side are measured in order to decrease the on-chip power control state. Finally the transmitting power is adjusted in a way to transmit only sufficient power for chip operation. This reduces the transmitting power. Therefore the power control unit in the implant has to control less excessive power.