A device for accounting for changes in characteristics of a transistor is presented. The device includes a transistor and a comparator receiving a feedback signal from the transistor and a reference signal. The comparator provides an output to a bias voltage generator. The bias voltage generator includes an input connected to the output of the comparator and an output connected to the transistor. In some embodiments of the invention the transistor is a double gate transistor and the bias voltage generator is applied to a top gate of the double gate transistor in order to control characteristics of the transistor such as turn on voltage.