Noise rejection circuitry and laser system using the same

Abstract

A controller including a closed loop servo system for a laser, or other entity is capable of substantial reductions in predictable, periodic noise such as the line noise induced by the source of alternating current electrical power, and in random noise as well. The servo circuit includes resources which develop a stored version of the predictable noise and uses the stored version of the predictable noise to compensate for the predictable noise. According to another aspect, the servo circuit includes resources which automatically adjust loop gain as gain in the entity being controlled and the loop as a whole system varies. The resources which generate the stored version of the predictable noise may be operated in either analog or digital formats. The sampling resources include, in an analog/digital embodiment, a plurality of charge holding devices, Multiplexing circuitry is coupled to the charge holding devices, and connects a selected charge holding device to a sample node which receives the feedback signal. Control circuits control the multiplexing circuitry to switch, in sequence, the plurality of charge holding devices to the sampling node in synchronism with the predictable periodic noise so that a stored version is developed in the plurality of charge storage devices. In addition, the servo circuit includes resources which automatically adjust loop gain as the slope of the laser system varies, which substantially reduces both random and periodic noise.