An integrating servo demodulator for hard disk drives

The design of a high-performance integrating servo demodulator circuit for hard disk-drive systems is described. This design implements a filter, demodulation of the normal and quadrature position error signals, off-track detector, and servo timing. The operating frequency range is 1 MHz to 6 MHz with pulse width (PW50) variation from 60 ns to 180 ns. The servo has a dedicated AGC (automatic gain control) loop with a 15-dB range. The linearity of the position error signal output is better than 3%. The circuits are implemented in 0.9-μm CMOS technology