International Business Machines Corporation

Peter Alan Gardner

Robert Duncan Commander

John Richard Taylor

A current-controlling circuit for producing either a constant current, independent of supply potential or a current which decreases with increasing supply potential and vice-versa. Three devices are connected together at a point such that the current in the first device and the current in the third device form the current in the second device. The current flowing in the first device is a mirror of the current flowing in a fourth device. When the supply potential increases, the increase in current in the first device at least equals the increase in current in the second device, so that the current in the third device does not increase. If the current in the third device decreases with increasing supply potential, it may be mirrored into subsequent devices which may then pass a constant current. The circuit may include an amplifying current mirror so that any change in current flowing in the first device is an amplified version of the change in current in the fourth device. The circuit may be implemented in field effect transistor technology. The amplitude of the current produced by the circuit is dependent on an input control voltage which is controlled by external means.

Current-controlling circuit

A data storage apparatus, such as an accessing head magnetic disk file, includes at least one data disk surface and a servo disk surface. In operation, a continuous position signal having high frequency components is derived from the servo surface, which has a quadature type servo signal prerecorded thereon. A circuit means modifies the derived position signal so that a substantially linear signal representing the displacement of the servo head from the servo track is obtained. A second position signal having a low frequency component is obtained from servo sector information registered on the data disk surface and together with the first position signal forms a hybrid position signal. This hybrid signal is used to control the movement of the data heads relative to the data tracks to ensure optimum transducing operation.

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Southampton, United Kingdom

Peter Alan Gardner