2.5 rad/sec/sup 2/ resolution digital output MEMS-based rotational accelerometer for HDD applications

Mechanical vibration of a HDD can cause head mis-positioning. This effect can be compensated by using the device presented in the following. It is a capacitive rotational accelerometer sensor which uses MEMS. The vibrations of the disk drive cause tiny rotational displacements of the moving part of the MEMS structure, which are measured by sensing the small variations in capacitance that they cause. Capacitance changes as small as 0.05 fF can be measured by the device. The device operates as follows: the minute rotational vibrations are detected and measured in order to generate a feed-forward correction signal for the voice coil drive circuit to keep the head in the correct position. This allows the track spacing to be reduced significantly, increasing the storage density per unit area. The circuit has been realized in a 0.61 /spl mu/m BiCMOS technology with an area of 9.5 mm/sup 2/. The power consumption is 150 mW from a single 5V supply.