We propose a fully differential detector with the properties of a diode detector. Thereto, the principle of the diode detector is implemented by an active control loop. By calculations, it is proven that the behavior is comparable to the conventional diode detector and reveals even better properties. Additionally, we show that it is possible to further linearize the transfer characteristic of the circuit and to achieve voltage gain at the same time. This is validated by measurements of a detector circuit which was implemented as part of an integrated circuit for an envelope following system.