Clocked power control circuit for inductively powered devices

Inductively powered devices are finding increasing use in many applications, such as biomedical implants and radio frequency identification (RFID) tags. In these systems, because of transmitter and receiver movements, the receiver coil may get close to the transmitter coil, which results in more than needed power delivered to the receiver load. This increases heat dissipated in the receiver circuit. In order to avoid overheating the receiver in such a high magnetic field (short coil separation distance) condition, the received power should be monitored and controlled. This paper introduces a clocked power control circuit integrated in the implant receiver, which is an independent, automatic power adjustment solution to limit heat dissipation with response to the coil separation distance. In this circuit, the rectified voltage across the load is monitored, and converted to a digital representation to selectively detune the receiver inductor-capacitor (LC) tank. To demonstrate this concept, a design example applied to inductively powered implants is given. Measurements on the prototype with a varied coil separation distance validate the desired power control functionality. Less power dissipation is achieved for the receiver compared to no power control condition.