Simple passive diode circuits cannot rectify small signals accurately. The forward bias potential of the diode acts as a constant barrier. By placing the diode inside the feedback loop of an op amp, the forward bias potential can be compensated for to a great extent. Both half-wave and full-wave circuits can be created in this fashion. Further, the addition of load capacitance can be used to create a simple envelope detector. On the downside, the frequency response of precision rectifiers is limited by the op amp(s) used.