JPH041923B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic tape recording device.

(Prior art) In order to improve distortion and dynamic range when recording magnetically on a magnetic tape using a recording head,
An alternating current bias current of a constant magnitude is superimposed on the signal current.

The effects of this AC bias are shown in Figures 2-4.
FIG. 2 shows the relationship between the amount of AC bias for low frequency signals and the maximum signal level that can be recorded on a magnetic tape. FIG. 3 shows the relationship between the amount of AC bias for high-frequency signals and the maximum signal level that can be recorded on a magnetic tape. Further, FIG. 4 shows the AC bias amount and third harmonic distortion rate characteristics for low frequency signals.

As shown in FIGS. 2 to 4, the optimum bias amount is different for the low-frequency signal and the high-frequency signal, so conventionally the bias amount has been set between the respective optimum points for both signals. Furthermore, since the optimum point of this bias amount differs depending on the type of magnetic tape used, the bias amount has been changed depending on the type of magnetic tape.

However, since the recorded signal itself has a bias effect, it is known that the substantial amount of bias during actual magnetic recording, that is, the effective amount of bias, becomes deeper depending on the signal.

That is, if a signal to be recorded includes a high frequency signal as well as a low frequency signal, the effective bias amount becomes deep because the high frequency signal exerts a bias effect on the low frequency signal. For this reason, there was a drawback that the operating point of the set bias was deeper than the optimum value. This phenomenon is known as the mutual bias effect.

Furthermore, since the high-frequency signal itself exerts a bias effect, there is also the drawback that the set operating point becomes deeper than the optimum value. This phenomenon is known as the self-bias effect.

In this way, if the AC bias added to the signal is kept at a constant level, the effective bias amount may become deeper depending on the signal.
In particular, the disadvantage was that the magnetic recording characteristics for high-frequency signals deteriorated.

A conventional example of a bias control device for eliminating such drawbacks is shown in FIG. The terminal voltage of the recording head 1 is set by a resistor 2 and a capacitor 3.
The signal is applied to the input of the peak detector 5 via the next low-pass filter 4. The output of the peak detector 5 is applied to an inverting input 7 of a differential amplifier 6, and a voltage from a reference voltage source 9 is applied to a non-inverting input 8 of the differential amplifier 6. The output of the differential amplifier 6 is applied as a gain control signal C to the gain control input 11 of the voltage control amplifier 10.
A part of the oscillation output B of the erasing oscillator 12 is applied to the input of the voltage control amplifier 10, and the output of the voltage control amplifier 10 is superimposed with the signal current A applied from the signal input terminal 13 in the adder 14 and sent to the recording head 1. is applied to. Also, the output of the erase oscillator 12 is output from the erase head 1.
5 is applied. Further, the magnetic tape 16 runs along the erasing head 15 and the magnetic head 1.

The operation of the conventional example shown in FIG. 5 is as follows. In other words, during magnetic recording, the magnetic tape 1
6 is demagnetized by passing an erase current applied from the erase oscillator 12 through the erase head 15, and then magnetically recorded. At this time, a part of the output B of the erase oscillator 12 is amplified by the voltage control amplifier 10 and applied to the recording head 1 as an alternating current bias, superimposed on the signal current A.

Furthermore, since the terminal characteristics of the recording head 1 are inductive, the impedance of the recording head 1 is proportional to the frequency. Therefore, the current flowing through the recording head 1 is detected by passing the terminal voltage of the recording head 1 through the low-pass filter 4 to convert it into a voltage inversely proportional to the frequency, and then detecting the voltage. here,
The cutoff frequency of the low-pass filter 4 is set to approximately the center frequency of the signal band to be recorded. This is because the bias effect of the signal itself, that is, the mutual bias effect and self-bias effect, becomes noticeable on the high frequency side of the signal band.

In this manner, the current flowing through the recording head 1 is detected by the low-pass filter 4, and the effective bias amount is further detected by the peak detector 5. The effective bias amount detected by the peak detector 5 is compared with the voltage of a reference voltage source 9 by a differential amplifier 6. Here, the voltage of the reference voltage source 9 is set to a voltage corresponding to the optimum bias amount depending on the type of magnetic tape used.

The output of the differential amplifier 6 serves as a control signal C to control the gain of the voltage control amplifier 10 to keep the effective bias amount constant. That is, when the effective bias amount is insufficient, the output voltage of the peak detector 5 that detects the effective bias amount becomes lower than the voltage of the reference voltage source 9, so that the output voltage of the differential amplifier 6 becomes higher. As a result, the gain of the voltage controlled amplifier 10 increases, and the effective bias amount increases.

On the other hand, when the effective bias amount is too large, the output voltage of the peak detector 5 that detects the effective bias amount becomes higher than the voltage of the reference voltage source 9, so the output voltage of the differential amplifier 6 becomes lower. As a result, the gain of the voltage controlled amplifier 10 is reduced and the effective bias amount is reduced.

As explained above, in the conventional example shown in FIG. 5, the drawback that the effective bias amount of the recording head 1 becomes deeper due to the bias effect of the recorded signal itself has been eliminated. For this reason, the characteristics particularly for high-frequency signals were improved.

(Problem to be Solved by the Invention) However, with this configuration, when excessive high-frequency signal components are included in the recorded signal, distortion is greater than in the conventional method of superimposing a constant AC bias. There was a drawback.

That is, when a signal with an excessively high frequency component is applied as the signal A to be recorded, a sufficient amount of bias will be obtained in the recording head 1 due to the self-bias effect of the signal itself. As described above, this state is detected by the low-pass filter 4 and the peak detector 5, and the voltage level applied to the non-inverting input terminal 7 of the differential amplifier 6 is increased. As a result, the output of the differential amplifier 6 becomes smaller, and the output of the voltage control amplifier 1 becomes smaller.
By reducing the gain of 0, the level of the AC bias signal added by the adder 4 is reduced. When an excessive high-frequency component signal is continuously applied, the voltage at terminal 7 becomes sufficiently higher than reference voltage 9, and differential amplifier 6
reduces its output to a level at which voltage control amplifier 10 no longer outputs an AC bias signal. In this state, if the high-frequency component of the excessive input to be recorded suddenly disappears, after the response time required by the low-pass filter 4 and the peak detector 5, the differential amplifier 6 causes the voltage-controlled amplifier 10 to output an AC bias signal. Although the output is changed, the recording head 1 is in an unbiased state during the response time. This means that the signal was recorded with large distortion. Moreover, the non-bias time is not only the response time mentioned above, but also the time required to recover from saturation and return to normal operation when the output of the differential amplifier 6 decreases to saturation. Become.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a bias control circuit that can maintain bias to a recording head even if an excessive high-frequency signal is input and the signal suddenly disappears.

(Means for Solving the Problems) A bias control circuit according to the present invention includes a bias compensation circuit that generates a signal necessary for a voltage control amplifier to output an AC bias signal to ensure a minimum amount of bias. , is characterized in that the sum of the output of this bias compensation circuit and the output of the differential amplifier is supplied as a control signal to the voltage control amplifier.

(Example) Next, the present invention will be described in more detail with reference to the drawings.

A bias control device according to an embodiment of the present invention is shown in FIG. In terms of configuration, in addition to the configuration of the conventional example shown in FIG. 5, a bias compensation circuit 17 is connected that limits the decrease in the output D of the differential amplifier 6 and compensates for the output of an AC bias signal. It's different.

According to this configuration, since the output E of the bias compensation circuit 17 is connected to the output D of the differential amplifier 6 and used as the control signal C', the output D of the differential amplifier 6 is set to a predetermined voltage determined by the compensation circuit 17. It cannot be lower than.

In other words, when the signal A to be recorded contains excessive high-frequency signal components and is sufficiently biased by the bias effect of the signal itself, the low-pass filter 4
Since the peak detector 5 detects that the bias amount is large via the peak detector 5, the voltage at the inverting input 7 of the differential amplifier 6 eventually becomes high. Even in such a case, the output of the differential amplifier 6 will never become lower than a predetermined voltage. Therefore, only the minimum amount of bias is always ensured from the output of the voltage controlled amplifier 10.

Therefore, even if the high-frequency signal contained in the signal A to be recorded suddenly disappears, as in the conventional example shown in FIG. 5, the non-biased state will not occur. Furthermore, since the output of the differential amplifier 6 is not saturated by the bias compensation circuit 17, the response time required for the operation in which a predetermined bias signal is extracted from the voltage control amplifier 10 can be shortened.

As is clear from the above explanation, the bias compensation circuit 17 prevents the output of the differential amplifier 6 from falling below a predetermined voltage, and on the other hand, when the voltage is higher than the same voltage, the output of the differential amplifier 6 Since the operation is performed without affecting the output, it can be constructed of a voltage source well known to those skilled in the art and a diode with this as an anode and the output of the differential amplifier 6 as a cathode.

(Effects of the Invention) As explained above, in the bias control device according to the present invention, when the signal to be recorded no longer contains a large high-frequency component, it does not become a non-bias state. Distortion no longer occurs.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of a bias control circuit according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the amount of AC bias for the reduced signal and the maximum signal level that can be recorded on a magnetic tape. FIG. 3 is a graph showing the relationship between the amount of AC bias for high frequency signals and the maximum signal level that can be recorded on a magnetic tape. FIG. 4 is a graph showing the AC bias amount and third harmonic distortion rate characteristics for a low frequency signal. FIG. 5 is a circuit block diagram showing a conventional bias control device. 1...Recording head, 2...Resistor, 3...Capacitor, 4...Low pass filter, 5...Peak detector, 6...Differential amplifier, 7...Inverting input of differential amplifier, 8...Difference Non-inverting input of dynamic amplifier, 9...
...Reference voltage source, 10...Voltage control amplifier, 11...
...Gain control input of voltage controlled amplifier, 12...Erasing oscillator, 13...Signal input terminal, 14...Adder, 15...Erasing head, 16...Magnetic tape,
17...Bias compensation circuit.

Claims (1)

[Claims] 1. Oscillator 12 that generates AC bias signal B
and a voltage control amplifier 10 that amplifies and outputs the AC bias signal B from the oscillator 12 with a gain corresponding to the control signal C', and adds the output of this voltage control amplifier 10 to the signal A to be recorded and generates a magnetic Adder 1 feeding head 1
4, a low-pass filter 4 that receives the output of the adder 14, a detector 5 that amplitude-detects the output of the low-pass filter 4, a reference voltage source 9 that generates a predetermined reference voltage, and an output of the detector 5. and a differential amplifier 6 that generates a signal D based on the difference between the reference voltage from the reference voltage source 9 and the reference voltage from the reference voltage source 9; Bias compensation circuit 17 that generates a signal E
A bias control circuit for a magnetic head, comprising the following: a sum of the signal D and the signal E is supplied to the voltage control amplifier 10 as the control signal C'.