Generating a quadrature seek signal from a discrete-time tracking error

Abstract

In an optical disk storage device wherein user data is demodulated from a light beam reflecting off data pits in tracks of an optical disk storage medium, a quadrature seek signal is generated indicative of the light beam crossing tracks of the optical disk during a seek operation. The quadrature seek signal is generated from a discrete-time tracking error signal (TES) and a discrete-time RF baseband signal. The discrete-time TES is generated according to the mode of operation, compact disk (CD) or digital video disk (DVD). In CD mode the TES is generated as the difference between E and F tracking photodiodes, and in DVD mode the TES is generated using a discrete-time differential phase detector (DPD). To generate the discrete-time RF baseband signal, the RF data signal (generated as the sum A+B+C+D of a four quadrant photodiode) is sampled at the channel rate and the RF data samples passed through a discrete-time envelope detector. The envelope detector extracts a discrete-time RF baseband signal which represents the light beam's location with respect to a track centerline. The discrete-time TES and baseband signals are synchronized and converted into binary square waves which form a quadrature seek signal (four transitions per track) for counting track crossings and for determining the radial seek direction.