US Patent 7420763 Disk drive control circuit and method

A servo control circuit provides seamless transition between seek and track modes while enabling both rapid seek mode operation and accurate tracking. The control circuit includes an analog-to-digital converter having a non-linear characteristic. The non-linear characteristic provides disproportionately large control voltages to derive speed and settling in the seek mode and essentially linear control voltages in the track mode to provide low noise and accurate tracking operation.