Closed-Loop Transductor-Compensated Class E Driver for Inductive Links

When a class E circuit is employed to drive an inductive link, very little tolerance is allowed on the inductance value of the transmitter coil. Deformable coils are thus not compatible with an open- loop class E design. By connecting a transductor in series with the transmitter inductance, it is possible to keep the total class E inductance constant, regardless of the transmitter coil deformation. This is achieved through a control loop that steers the transductor to the appropriate inductance value. For the realized closed-loop circuit, class E regime is maintained for inductance variations of the transmitter coil of up to 27 %. The principal advantage of transductor control compared to earlier reported techniques, is the fixed frequency of operation.