Micro Linear Corp, San Jose claims to have the first chip set for hybrid servo head control in high-capacity disk drives. It says the set is designed to be used in 3.5 and 5.25 drives with capacities greater than 1Gb and can also be used in design of higher capacity 1.8 drives. It works with a signal processor chip to keep the read-write head positioned over the tracks on the platter during read and write operations and implements hybrid servo control, which combines two servo methods to seek and maintain the position of read-write heads accurately on disks with track densities up to 3,000 tracks per inch, the company said. The hybrid servo technique combines a dedicated servo scheme, which stores servo tracking information on a separate platter, and an embedded servo scheme, which intermixes servo tracking information with the data on all platters. The set consists of the ML4535 Area Detection Based Hybrid Servo Demodulator chip and the ML2377 DSP Analogue Input-Output Peripheral chip. The ML4535 provides the circuitry to handle both dedicated and embedded servo signals and to determine how far the head is off track, it uses an area detection method, offering better noise rejection and lower soft error rates than the conventional peak detection methods. A servo algorithm running on the signal processor continually monitors the position of the head over the track using digital position information from the ML2377. It uses the ML2377’s 10-bit digital-to-analogue converter to drive the voice coil motor to put the head back on track, and the ML2377 is also used in the spindle motor control loop that keeps the platter spinning at a constant speed; both are sampling now, at $9.95 and $6.55 respectively for 1,000-up; volume in autumn.
