A novel adaptive biasing principle to reduce the stand-by power dissipation without affecting the transient performance of low-power topologies is presented. The circuit gives an output current which is dependent on the applied input differential voltage. If small signal sensitivity is required, the differential sensitivity can be improved by introducing a very small biasing current, whose task is the compensation of the threshold voltages of the transistors. The current value has to be set according to the transient performance constraints. The proposed topology, proved to be applicable to both bipolar and CMOS technologies, can be utilized in low-voltage low-power operational amplifiers, in particular for the biasing of the input stage. In this paper, a study of the large signal circuit behaviour, for both the bipolar and the CMOS technologies, is developed and basic design rules, concerning the setting of minimum and maximum output currents, are given. The agreement between theoretical calculations and Spice simulations makes these results very useful for the circuit design.