A phase locked loop system or other second order feedback system whose natural frequency scales with its output and whose damping factor remains constant includes a filter circuit having a scaling channel for scaling the error, an integrating channel for integrating the error, and a summing circuit for combining the scaled error and integrated error; an integrator circuit responsive to the summing circuit to produce an output signal, the gain of the integrator circuit being proportional to its output signal; and a control circuit for controlling the gain of the integrating channel proportional to the output signal and maintaining constant the ratio of and scaling the product of the unity gained frequency and the zero frequency of the feedback system to keep constant the damping factor and to scale the natural frequency of the feedback system with the output signal, respectively.