SERVO CONTROL USING CONTINUOUS POSITION ERROR SIGNAL WITH HIGH ORDER POLYNOMIAL COMPONENT

An apparatus and method for improved servo control in a disc drive. A rotatable disc has first, second, third and fourth radially staggered servo burst patterns which define a plurality of concentric tracks. An actuator assembly supports a transducing head adjacent the tracks. A servo circuit combines respective at least third order polynomial functions of burst signals from the first and second, and third and fourth, burst patterns to generate a continuous function position error signal (PES) with normalized absolute magnitudes of 0 when the head is positioned at track centers, 0.5 at track boundaries, and 0.25 at quarter-track locations, and with substantially linear slope therebetween. The servo circuit applies current to an actuator motor to position of the head relative to a selected track in relation to the magnitude of the PES.