An implantable analyte sensor (12) including a sensor body substantially formed from a water vapor permeable material and electrical components encapsulated within the sensor body, wherein the electrical components comprise RF circuitry (38) and an antenna (42) adapted for RF transmission from the sensor (12) in vivo to a receiver (14) ex vivo, wherein the RF circuitry (38) is spaced a fixed distance from the sensor body so as to support a dielectric constant that enables RF transmission between the sensor (12) in vivo to the receiver (14) ex vivo. The electrochemical glucose sensor comprises a three-electrode system (54) comprising an electrochemical cell comprising a working electrode (54a), reference electrode (54b), and counter electrode (54c)； and a potentiostat (24) configured to control a potential between the working electrode and the reference electrode, wherein an allowable range for the counter electrode voltage is set sufficiently wide such that the glucose sensor is configured to react with other reducible species when oxygen becomes limited and sufficiently narrow to ensure the circuitry does not allow excessive current draw or bubble formation to occur when in use.
