A Monolithic All-CMOS Embedded Servo Channel for Hard Disk Drives

This paper describes the architecture and implementation of a Hard Disk Drive (HDD) Embedded Servo Channel chip. The Servo Channel monitors the position of the read-write heads. The heads' positions are then adjusted to seek the required track and to maintain acceptable error rates while reading from or writing to the disk; the chip implements the full Embedded Servo demodulation process. Positional information is extracted from a differential input voltage at 10MHz and can then be read from the chip as four 10-bit words. New head positioning information can be sent to the chip as a 10-bit input word. The chip outputs a head positioning control voltage proportional to the input code. Using the chip, a servo loop can be implemented for head positioning. The device has been fabricated in 1.0 micron CMOS. The die area is 144mil × 142mil (3.7mm × 3.6mm). Power dissipation is 125mW nominal, dropping to 4mW nominal in powerdown mode. Packages are 28-lead SOIC and 32-lead TSOP.