Abstract: For the purpose of providing sector-address information on optical disks, a robust header is realized by utilizing a very simple encoding method that allows asynchronous reading. In order to provide robustness and reliability, the header uses a biphase data format to encode addressing information. The embossed header is further configured with redundant address-fields in a checkerboard pattern between adjacent tracks, in order to provide robustness for media-contamination. Each address-field starts with a unique address-mark and ends with parity-check information to provide reliable error-detection. The entire header can be decoded without the need for a slice-level, thus making it very tolerant to amplitude-variations and DC-offset variations. By combining these characteristics, a header is achieved which is reliable and inherently resistant to failures in providing sector-address information on optical disks.

Abstract: Rate of change of the angle .theta. conveyed by a three-wire synchro signal is developed as an inherently normalized signal (d.theta./dt) by dividing N sin .theta. (d.theta./dt) signals by N sin .theta. signals and N cos .theta. (d.theta./dt) signals by N cos .theta. signals over selected ones of contiguous segments of a full 360.degree. range of .theta. where the divisor signals do not go through zero. The N sin .theta. and N cos .theta. signals are normalized outputs of dividers which divide synchro carrier reference demodulated sin .theta. and cos .theta. signals by a synchro carrier reference level signal. N sin .theta. and N cos .theta. signals are differentiated to derive the N sin (d.theta./dt) and N cos .theta. (d.theta./dt) signals. Logic circuitry switches appropriately signed ones of the signals as divisor and dividend inputs to an output divider whose output is (d.theta.