EXTERNAL CHARGER FOR AN IMPLANTABLE MEDICAL DEVICE HAVING TWO SENSE COILS CONCENTRIC WITH A CHARGING COIL FOR DETERMINING POSITION

An external charger for wirelessly providing energy to an implantable medical device (IMD), comprises a charging coil configured when energized by a drive signal to produce a magnetic field to wirelessly provide energy to the IMD and a first sense coil comprising one or more turns at a first radius and a second sense coil comprising one or more turns at a second radius larger than the first radius, wherein the first sense coil is configured to be induced by the magnetic field with a first induced signal, and wherein the second sense coil is induced with a second induced signal, wherein the first and second sense coils are concentric with the charging coil. The external charger further comprises a controller circuitry configured to determine a first parameter from the first induced signal and a second parameter from the second induced signal, and is further configured to determine using at least the first and second parameters the position of the charging coil with respect to the IMD.