High density servo signal detection for accurate head positioning

A high density servo pattern encoding and position signal detection method with high signal-to-noise ratio, in order to realize accurate head positioning for higher track density in magnetic disk drives, has been developed. Servo pattern encoding is composed of a two-bit element with magnetization opposed according to odd and even servo tracks. The position signal is detected by differentiating the two-bit pulses. This is effective in suppressing undesirable lower frequency noises. With these techniques, a 5 dB signal-to-noise ratio improvement of the position signal and high accuracy with ± 0.15 μm positioning errors are experimentally achieved.