Multi-rate digital control with interlacing and its application to hard disk drive servo

This paper presents a design method for a multi-rate digital controller with interlacing and its application to hard disk drives. In general, a digital controller contains slows modes and fast modes. The slow-mode portion can be updated less frequently in order to reduce the computational load. In other words, one can decrease the sampling rate of the slow-mode controller. Hence, the resulting multi-rate digital controller is composed of a fast-mode controller with high sampling rate and a slow-mode controller with high sampling rate. The amount of computation is uniformly reduced by interlacing the slow-mode control outputs. This design method is evaluated by simulation and the advantage of multi-rate control with interlacing is demonstrated.