JPS61120304A - Bias controlling device - Google Patents

Abstract

PURPOSE:To prevent destruction of a voltage control amplifier or while of a bias controlling device in the bias controlling device in which output of the voltage control amplifier is applied superposing on recording signals to a recording head by connecting a limiter to the voltage control amplifier. CONSTITUTION:In a normal state, current that flows in the recording head 1 is detected by a low-pass filter 4, and the quantity of effective bias is detected by a peak detector 5. The quantity of effective bias is compared with voltage of a reference voltage source 9 by a comparator 6, and output of the comparator 6 controls gain of the voltage control amplifier 10 to keep the quantity of effective bias constant. Output of the voltage control amplifier 10 is superposed on signal current applied from a signal input terminal 13 by an adder 14 and applied to the recording head 1. In the case where gain control of the voltage control amplifier 10 becomes impossible due to, for instance, the grounding of the inputting section of the peak detector 5, the generation of excessive output of the voltage control amplifier 10 is prevented by the limiter 17.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a magnetic tape recording device.

[Conventional technology]

In order to improve distortion and dynamic range when performing magnetic recording on a magnetic tape using a recording head, it is a known technique to superimpose an alternating current bias current of a certain magnitude on a signal current.

The effects of this AC bias are shown in Figures 3-5.

FIG. 3 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. 4 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. FIG. 5 shows the AC bias amount and third harmonic distortion rate characteristics for low frequency signals.

As shown in FIGS. 3 to 5, the optimum bias amount is different for the low-frequency signal and the high-frequency signal, so the bias amount is set between the respective optimum points for both signals. Furthermore, since the optimum point of the bias amount differs depending on the four types of magnetic tape used, the bias amount has been switched depending on the type of magnetic tape.

However, it is known that since the recorded signal itself has a bias effect, the actual bias amount, that is, the effective bias amount during actual magnetic recording 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 effect is known as the mutual bias effect.

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

As explained above, in the method of setting the alternating current bias applied superimposed on the signal to a constant magnitude, the effective bias amount may become deeper depending on the signal. For this reason, there was a drawback that the magnetic recording characteristics, especially for high-frequency signals, deteriorated.

A conventional example of the bias system @@fft for eliminating such drawbacks is shown in Fig. t46. In FIG. 6, 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 sent to the comparator 6.
0 is applied to the inverting input cuff, and a voltage from a reference voltage source 9 is applied to the non-inverting input 8 of the comparator 6. The output of the comparator 6 is applied to the gain control input 11 of the voltage controlled amplifier 10, and the input of the voltage controlled amplifier 10 is applied to the cancellation oscillator 12.
A part of the oscillation output of is applied to the stain pressure control amplifier 10.
The output is superimposed with the signal current applied from the signal input terminal 13 in an adder 14 and applied to the recording head 1. Further, the output of the erase oscillator 12 is applied to the erase head 15. Further, the magnetic tape 16 runs along the erasing head 15 and the recording head 1.

The operation of the conventional example shown in FIG. 6 is as follows.

That is, during magnetic recording, the magnetic tape 1G is normally demagnetized by passing an erase current given by the erase oscillator 12 to the erase head 15, and then magnetically recorded. At this time, the erase oscillator 1
A part of the output of the recording head 2 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.

Furthermore, since the terminal characteristics of the recording head 1 exhibit inductive properties, the impedance of the recording head 1 is proportional to the frequency. Therefore, the current flowing through the print head IK is detected by passing the terminal voltage of the print head 1 through a low-pass filter 4 to make it 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 way, 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 comparator 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 comparator 6 controls 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 #, 9, so the output voltage of the comparator 6 becomes high.

As a result, the gain of the voltage controlled amplifier 10 increases and the effective bias amount increases.

Conversely, if the effective bias amount is too large, the output voltage of the peak detector 5 that has detected the effective bias amount is the reference voltage source 9.
, the output voltage of the comparator 6 becomes lower, and as a result, the gain of the voltage control amplifier 10 becomes smaller and the effective bias amount decreases.

As explained above, in the conventional example shown in FIG. 6, 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 have been improved.

[Problem that the invention seeks to solve]

However, with the above-described conventional bias control device, the recording head 1. Low pass filter 4. Peak detector 5. Comparator 6. Pressure control amplifier 10. Adder 14. If a part of the loop consisting of
If the gain control of the voltage controlled amplifier 10 becomes inoperable,
The voltage controlled amplifier 10 has the disadvantage that it generates an excessive output, which may destroy the voltage controlled amplifier 10 or the entire bias control device.

For example, if the input part of the peak detector 50 has a ground fault, the input of the peak detector 50 becomes "0".

The output voltage of the peak detector 5 and the voltage at the inverting input cuff of the comparator 60 become lower than the voltage of the reference voltage source 9, so the output voltage of the comparator 6 becomes higher and the gain of the voltage control amplifier 10 becomes larger. , operates to increase the effective bias amount. However, even if the effective bias increases, the peak detector 5
Since the input part of is grounded, the peak detector 5 detects that the effective bias amount remains at 101, and the voltage control amplifier 10 operates to further increase the effective bias value, so that the voltage The control amplifier 10 has the disadvantage that it generates excessive output and may be destroyed.

[Means for solving problems]

In the bias control device of the present invention, the terminal voltage of the recording head is applied to the input of a low-pass filter, the output of this low-pass filter is connected to the input of a peak detector,
The output of this peak detector and a reference voltage are applied to respective inputs of a comparator, the output of which is connected to the gain control input of a voltage controlled amplifier, to which the output of the excavator is applied. In a bias control device in which the output of a voltage control amplifier is applied to the recording head in a manner superimposed on the recording signal, a limiter is applied to the voltage control amplifier.
It is characterized by being connected.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing the principle of the present invention. For the sake of simplicity, parts corresponding to those in FIG. 6, which shows a conventional bias control device, are given the same reference numerals. The configuration is the same as that of the conventional example shown in the IS6 diagram except that a limiter 17 is added to the voltage control amplifier.

The bias control device according to the present invention shown in FIG. 1 operates in the same way as the conventional example shown in FIG. 6 in a normal state. That is, the current flowing through the recording hect 1 is detected by the low-pass filter 4, and the effective bias amount is further detected by the peak detector 5. This effective bias amount is compared with the voltage of a reference voltage source 9 by a comparator 6, and the output of the comparator 6 controls the gain of the voltage control amplifier 10 to keep the effective bias amount constant.

However, the bias control device according to the present invention does not allow the recording head 1. Low pass filter 4. Peak detector 5. Comparator 6
．． Voltage controlled amplifier 10. If the gain control of the voltage control amplifier 10 becomes inoperable due to a part of the loop consisting of the adder 14 being cut or grounded, the limiter 17 is connected to the voltage control amplifier 10. Therefore, the output of the stain pressure control amplifier 10 can be limited, and generation of excessive output can be prevented.

For example, as in the case explained in the conventional example, when the input part of the peak detector 5 is grounded, the input of the peak detector 5 becomes @O'', and the output voltage of the peak detector 5 is Since the voltage at the inverting input cuff of the comparator 60 becomes lower than the voltage of the reference voltage source 9, the output voltage of the comparator 6 becomes higher and the gain of the voltage control amplifier 10 increases, operating to increase the effective bias amount. However, even if the effective bias amount increases, since the input part of the peak detector 50 is grounded, the effective bias amount of the peak detector 5 will be 60.
It is detected that the voltage control amplifier 10 remains in the state #, and the voltage control amplifier 10 attempts to operate to further increase the effective bias amount, but the output of the voltage control amplifier 10
The output will not be higher than the output set by the limiter 17 connected to the output, and the occurrence of a catastrophic output can be prevented.

FIG. 2 shows an embodiment of the voltage control amplifier 10 and limiter 17 of the bias control device according to the present invention. Comparator 6
The output voltage is the gain control power 11 of the voltage control amplifier 10.
(NPN) run raster 32. It is converted into a current by resistor 19 and resistor 20. The current is PNP
) C-B with the base and collector of transistor 28 shorted
It is inverted by a current mirror circuit composed of a short diode and a PNP transistor 29, and the PN
It is switched by a differential amplifier composed of P transistors 30 and 31, and resistors 21 to 27 and NPN
Amplified by a current mirror circuit constituted by transistors 33 to 38 and a transformer 41,
4, the signal is superimposed with the audio signal and applied to the recording head 1 and the low-pass filter 4.

The limiter circuit 17 is constituted by an E-B Zener diode whose base and collector of an NPN transistor 39 are shorted. If the Zener voltage of this E-B Zener diode is Vz, the emitter-base voltage of the NPN transistor is VBK, and the resistance value of resistor 19 is R19, then the maximum value of the current flowing through resistor 19 is: , hako. Robust = (vz
-V)/R19. Since the output of the voltage controlled amplifier 1o is proportional to the current flowing through the resistor 19, the maximum value of the output of the voltage controlled amplifier is limited by determining the maximum value of the current flowing through the resistor 19 using the transistors 32 and 39 and the resistor 19. be able to.

〔Effect of the invention〕

As described above, the bias control device according to the present invention can prevent the voltage control amplifier from generating an excessive output when gain control is impossible, thereby preventing damage to the voltage control amplifier or the entire bias control device. effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the principle of the bias control device according to the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the main part thereof.
i! This is Figure 8. Figure 3 is a graph showing the relationship between the amount of AC bias for low frequency signals and the maximum signal level that can be recorded on magnetic tape, and Figure 4 is the graph showing the relationship between the amount of AC bias for high frequency signals and the maximum signal level that can be recorded on magnetic tape. Graph showing 5th
The figure is a graph showing the AC bias amount and third harmonic distortion rate characteristics for a low frequency signal. FIG. 6 is a block diagram showing a conventional bias control device. 1...recording head, 2...resistance, 3.
... Capacitor, 4 ... Low pass filter, 5 ... Peak detector, 6 ... Comparator, 7 ... Inverting input of comparator , 8...-
・Comparator non-inverting input, 9...Reference voltage source, 1
0... Voltage controlled 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...Limiter-118~2
7...Resistor, 28-31...PNP) transistor, 32-39...NPN) transistor, 40...Capacitor, 41... Trance. Agent: Susumu Uchihara, patent attorney 1.・1. ,=,,
,,,,,,,. Figure 2 Figure 3

Claims (1)

[Claims] The terminal voltage of the recording head is applied to the input of a low-pass filter, the output of the low-pass filter is connected to the input of a peak detector, the output of the peak detector and a reference voltage are applied to respective inputs of a comparator, The output of the comparator is connected to a gain control input of a voltage controlled amplifier, the output of an oscillator is coupled to the input of the voltage controlled amplifier, and the output of the voltage controlled amplifier is superimposed on a recording signal to the recording head. A bias control device configured to apply voltage to the voltage control amplifier, characterized in that a limiter is connected to the voltage control amplifier.