JPH0550064B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a control signal reproducing device used in a magnetic recording/reproducing device such as a two-rotating head type helical scan type video tape recorder.

Conventional configuration and its problems In general, when reproducing control signals using a magnetoresistive head (hereinafter referred to as an MR head), since the MR head is known to have a large temperature dependence, AC coupling is required. After removing the temperature dependence of the MR head, amplification is performed. However, this method has a problem in that the control signal cannot be reproduced when the magnetic tape is running at an extremely low speed or is stopped.

FIG. 1 shows the main circuit configuration of a conventional example. In FIG. 1, a predetermined voltage is applied from terminal 2 to MR head ₁ through resistor R1. Resistor _R1 is selected to have a sufficiently large resistance value so that almost all current flows through MR head 1. The control signal detected by the MR head 1 has a DC component, and this DC component varies depending on the temperature dependence of the MR head 1. Therefore, after removing the DC component with a capacitor C, the control signal is connected to an operational amplifier. Supply to 4. operational amplifier 4
The gain of is determined by resistors R2 and R3, and an amplified control signal that is independent of temperature is obtained from the output terminal 3. The control signal obtained from the output terminal 3 is supplied to a pulse detection circuit (not shown) composed of a comparator and the like, and is extracted as a control pulse.

Purpose of the Invention The present invention eliminates the above-mentioned drawbacks of the prior art, and eliminates the temperature dependence of the MR head, and also handles control signals down to direct current, thereby making it possible to run magnetic tapes at ultra-low speeds. To provide a device capable of reproducing control signals stably even when stopped and when the control signal is stopped.

Structure of the Invention The apparatus of the present invention includes a reproduction control signal taken out by an MR head and amplified by a reproduction circuit, and a pulse signal indicating the rotation angle of a rotating body that rotates as a magnetic tape runs. (below,
By calculating the difference between the FG signal and the delayed control signal, which is delayed in units of FG signals, the temperature dependence of the MR head is removed and DC reproduction of the control signal is realized.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 2, a predetermined voltage is applied from a terminal 11 to an MR head 13 through a resistor 12. The value of the resistor 12 is selected to be sufficiently large so that a substantially constant current flows through the MR head 13. The control signal detected by the MR head 13 (referred to as the original control signal) is sent to the reproducing circuit 14.
is amplified by Since the direct current component of the control original signal varies depending on the temperature dependence of the MR head 13, the reproducing circuit 14 should have a dynamic range commensurate with the variation. Also,
In order to set the operating point of the reproducing circuit 14 to an optimum value, a DC bias may be applied from the terminal 15. Next, the output signal of the reproduction circuit 14 is converted into a digital signal by an A/D (analog/digital) converter 16 and supplied to a sample and hold circuit 17. sample·
The hold circuit 17 is also supplied with an FG signal generated by the FG signal generation circuit 18.
The signal controls sampling and holding operations. Here, the FG signal generation circuit 18 is
A well-known magnetic recording/reproducing device such as a video tape recorder is composed of a slitted disc that rotates together with a capstan shaft (not shown) provided to control the running speed of the magnetic tape, a fixed photo interrupter, etc. A circuit that amplifies and shapes the waveform of a signal obtained from a rotary encoder (not shown) to suit the apparatus of this embodiment, and a pulse-shaped signal corresponding to tape running obtained from its output. FG
It is called a signal. Again in Figure 2, the sample
The output signal of the hold circuit 17 is supplied to a D/A (digital/analog) converter 20 and a shift register 19. The shift register 19 is supplied with the FG signal, and is delayed in units of FG signals. The output signal of the shift register 19 is converted into an analog signal by the D/A converter 21. A signal waveform 101 in FIG. 3a schematically shows the output signal waveform of the D/A converter 20 in FIG. 2, and a signal waveform 102 schematically shows the output signal waveform of the D/A converter 21 in FIG. It is shown schematically. Referring again to FIG. 2, the output signals of the D/A converters 20 and 21 are both supplied to a difference calculation circuit 22, where a difference calculation is performed. The output signal of the difference calculation circuit 22 is output from the output terminal 23.
A control pulse is obtained by a pulse detection circuit (not shown) comprising a comparator and the like.

A signal waveform 103 in FIG. 3b shows the output waveform of the difference calculation circuit in FIG. This output waveform can be considered to have the temperature dependence of the MR head (13 in FIG. 2) removed. Assuming that the temperature of the MR head changes within the delay time of the shift register 19, the output waveform of the D/A converter 21 (102 in FIG. 3a) will change from the output waveform of the D/A converter 20 (101 in FIG. 3a). ), the DC voltage component will change. However, the delay time of the shift register 19 is set at most one second, and during that time the MR
In reality, it is impossible for the head temperature to fluctuate greatly. Therefore, the DC voltage components of the output waveform of the D/A converter 21 and the output waveform of the D/A converter 20 can be considered to be almost equal, and by taking the difference between them, the DC voltage component, that is, the temperature-dependent component can be removed. It can be considered possible.

Effects of the Invention As described above, the present invention eliminates the temperature dependence of the MR head by using a method of performing difference calculations, and can handle control signals up to the DC region. Therefore, it is possible to stably obtain a control signal even when the magnetic tape is running at extremely low speed and when it is stopped, which is extremely advantageous for monitoring and controlling the tape position. Furthermore, even when detecting changes in magnetic flux using a Hall element that is said to have temperature dependence like an MR element, as in the present invention, an output signal from the Hall element and a delayed signal are generated. , by calculating the difference between these two signals, the temperature dependence of the Hall element is removed,
Direct current reproduction of the Hall element output signal can be performed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional control signal reproducing device, FIG. 2 is a configuration diagram of an embodiment of the present invention, and FIGS. 3a and 3b are signal waveform diagrams in FIG. 2. 11...Terminal, 12...Resistor, 13...MR
Head, 14...Reproduction circuit, 16...A/D converter, 17...Sample/hold circuit, 18
...FG signal generation circuit, 19...shift register,
20, 21...D/A converter, 22...Difference calculation circuit, 23...Output terminal.

Claims (1)

[Claims] 1. A magnetoresistive magnetic head that reproduces control signals recorded on a magnetic tape, a reproduction circuit, and a pulse signal generation circuit that generates pulses indicating the rotation angle of a rotating body that rotates as the magnetic tape runs. It is equipped with a delay circuit and a difference calculation circuit that calculates the difference between two signals, inputs the output signal of the magnetic head to the regeneration circuit, and converts the output signal of the regeneration circuit into the output pulse of the pulse signal generation circuit. input the signal to the delay circuit controlled by the signal, input the output signal of the reproduction circuit and the output signal of the delay circuit to the difference calculation circuit, and obtain a control signal from the output terminal of the difference calculation circuit. A control signal reproducing device characterized in that it is configured as follows.