Robert Carl Barrett

Timing-based track-following servo for linear tape systems

Timing-Based Servo (TBS) is a unique servo technology developed specifically for linear tape drives. In TBS systems, recorded servo patterns consist of transitions with two different azimuthal slopes, and head position is derived from the relative timing of pulses generated by a narrow head reading the pattern. Position signals are nearly perfectly linear over multiple track widths, and highly immune to errors caused by head wear, head instability, debris, and media defects. Multitrack TBS servo patterns are written in a single pass using a novel multigap horizontal thin film servo writing head. The design of the pattern and its dimensions are optimized to provide sampling rate, noise level, and error rate suitable for the intended application. An all-digital TBS servo channel provides a speed-invariant position signal. Pattern recognition algorithms detect servo signal errors, providing a highly robust servo signal. Test results show approximately I pm linearity and 0.3 /spl mu/m noise level over a width of 400 /spl mu/m width with 18 kHz sampling rate. The TBS pattern allows flexibility for encoding additional information without affecting the position signal. By shifting transitions as little as 0.1 /spl mu/m from their nominal pattern positions, a low error rate serial bitstream can be encoded in the servo track. This technique allows tape longitudinal position to be encoded with a resolution of about 2 mm, allowing efficient and precise tape transport control based on the servo signal alone.

Data storage in NOS: lifetime and carrier-to-noise measurements

Charge trapping in thin films of silicon nitride has long been studied for use as a nonvolatile semiconductor memory. Recently, this technology has been combined with scanned probe technologies with the sharp probe tip serving as the upper electrode in a Si/sub 3/N/sub 4/-SiO/sub 2/-Si (NOS) structure. By applying a voltage pulse between the tip and silicon substrate, charge carriers can be made to tunnel through the oxide and be trapped in the nitride. It has been proposed that such a system could be used as a high density data storage device. We have explored some of the issues related to such an application, including data lifetime and data rates. In high temperature aging studies, no sign of charge spreading was seen after 9 months at 150/spl deg/C. From the logarithmic nature of the charge decay, we predict that the initial written charge should have a lifetime in excess of 30 years at 150/spl deg/C. At a data rate of 500 kHz, a carrier-to-noise ratio (CNR) of approximately 60 dB in a 5-kHz bandwidth was demonstrated. A model based on the presence of trapped charge in oxide or nitride is used to explain a 45-dB discrepancy between the calculated and measured CNR. >

Negative inertia: a dynamic pointing function

In-keyboard isometric joysticks can give better performance than mice for mixed typing/pointing tasks. The continuing challenge is to improve such devices to the point that they are preferable even for pure pointing tasks. Previous work has improved joystick performance by considering user perception and motor skills. This paper considers the dynamics of the pointing operation. A dynamic transfer function for an isometric joystick is described which amplifies changes in the applied force to increase responsiveness without loss of control. User tests show a 7.8 +/3.5% performance improvement over a standard non-dynamic joystick. This feature has been incorporated into the TrackPoint III from IBM.