Sample data position error signal detection for digital sector servo

Abstract

A sample data position error signal detection means is described. This invention is suited for use in a digital sector servo in a magnetic media disk drive environment. In particular, the invention relates to the detection and presentation in digital form of position error signals (PES) representative of magnitude and sign of recording head displacement from a track centerline. The circuits disclosed provide a digital representation of PES suitable for direct application to a digital signal processor which controls overall servo positioning operations. The invention detects the PES by an integration method and incorporates the innovation of requiring only two integrators to demodulate a PES having an arbitrarily large number of phases. The invention uses a phaselock oscillator having a hybrid digital/analog phase detector to generate the coherent carrier sequence for synchronous detection of PES. A further innovation of the invention is the use of a fully digital automatic gain control circuit (AGC). Prior embodiments of position demodulators have employed analog AGC approaches which are more sensitive to disk surface flaws and which cannot easily be made adaptive. Furthermore, such features as exponentiation of AGC gain control level can be readily incorporated with no penalty to circuit complexity.