A method and system that provides for execution of a first calibration sequence, such as upon initialization of a system, to establish an operation value, which utilizes an algorithm intended to be exhaustive, and executing a second calibration sequence from time to time, to measure drift in the parameter, and to update the operation value in response to the measured drift. In a disc drive employing the object lens actuation, stable writingreading operation is implemented by always keeping a focal point of an object lens at a predetermined track of a recording surface of the disc even when being under the action of external perturbations such as a vertical deviation or a radial deviation of the disc, resulting in improved reliability. According to a second aspect, a recycling process is used that significantly increases the yield of desired product. A loop current adaptor adapts a ratio of the first and second currents by adjusting a back gate bias voltage applied to a back gate of loop transistor of the feedback loop.