A sample data position error signal detection means is described. This invention is suited for use in a digital sector servo in a magnetic media disk drive environment. In particular, the invention relates to the detection and presentation in digital form of position error signals (PES) representative of magnitude and sign of recording head displacement from a track centerline. The circuits disclosed provide a digital representation of PES suitable for direct application to a digital signal processor which controls overall servo positioning operations. The invention detects the PES by an integration method and incorporates the innovation of requiring only two integrators to demodulate a PES having an arbitrarily large number of phases. The invention uses a phaselock oscillator having a hybrid digital/analog phase detector to generate the coherent carrier sequence for synchronous detection of PES. A further innovation of the invention is the use of a fully digital automatic gain control circuit (AGC). Prior embodiments of position demodulators have employed analog AGC approaches which are more sensitive to disk surface flaws and which cannot easily be made adaptive. Furthermore, such features as exponentiation of AGC gain control level can be readily incorporated with no penalty to circuit complexity.

A MR head amplifier of the present invention prevents a base potential of a transistor which supplies a current to a MR element from changing in a moment when the MR element changes from a write-state to a read-state. The MR head amplifier includes a loop amplifier that has a non-inverted input terminal connected to one end of a first transistor which supplies a current to a MR element and an inverted input terminal connected to one end of a second transistor which is supplied with a constant current through a constant current source. An output terminal of the loop amplifier is feedback to a base terminal of the first transistor via a first switch and one end of a capacitor whose other end is connected to a ground is connected to an output terminal of the first switch. The loop amplifier includes a second switch connected between the output terminal of the first switch and the base terminal of the first transistor, the second switch being closed during read-state and opened during write-state.

A dynamic head position tracking control for a magnetic tape playback system employs a detected dither signal to determine the elevational position of a pair of magnetic transducing heads relative to tracks of recorded information being scanned by the heads. This detection is carried out at several locations along the lengths of the tracks being scanned, and a value is stored for each of the locations. Based upon the stored information, an estimation is made of a position value for the first location along the length of the tracks. This estimation is determined from a weighted extrapolation of the following two samples taken during the scan of the track. The elevational position of the heads is then dynamically controlled in accordance with the actual and estimated head position values.

A control circuit for a helical scan playback, in which a rotary head is moved transversely by a varying amount. The transverse movement can be either a multi-valued tracking position error correction signal or a saw-tooth waveform, effective during a location data strip, for compensating for the fast movement of the tape during a scan operation.

A video signal reproducing apparatus comprises a rotary magnetic head which reproduces a video signal recorded on a magnetic tape, a rotator which rotates the rotary magnetic head to cause the same to scan the magnetic tape intermittently along a oblique path thereon, a head supporting member, such as a compound piezoelectric plate element, which supports the rotary magnetic head to rotate in accordance with the rotation of the rotator and to shift the position of the rotary magnetic head in the direction of the axis for rotation thereof in response to the level of a control signal supplied thereto, and a signal generator which produces a signal acting as the control signal in a "trick" reproducing mode and having such level variations as to cause the head supporting member to have a swinging movement in a period in which the rotary magnetic head is not in contact with the magnetic head, which affects to cancel a swinging movement of the head supporting member occuring in a period in which the rotary magnetic head scans the magnetic tape.