JPH0253205A - Magnetic recording amplifier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording amplifier in which the recording current applied to the recording head section does not change even if the impedance of the recording head section changes.

[Conventional technology]

FIG. 4 is a circuit diagram showing a magnetic recording amplifier conventionally used in a VTR. In the figure, 1 is an input terminal into which a signal to be recorded is input, 2 is a recording amplifier that amplifies the signal input from input terminal 1, and A is a recording amplifier that converts the output of the recording amplifier into a recording current and sends it to the recording head section B. This is the output stage that supplies the The output stage A and the recording head section B are connected via a capacitor C.

Output stage A includes NPN transistors Q1 and Q3, PNP
It is composed of transistors Q2 and Q4, constant current sources 11 and I2. Transistors Q1 and Q2 are buffer transistors, and the bases of these transistors are connected to the output of the recording amplifier 2. The transistor Q1 has an emitter connected to GND via a constant current source 11, and a collector connected to a power supply V. 0, respectively. The emitter of the transistor Q2 is connected to the power supply ■ through the constant current source ■2. to 0,
Collectors are each connected to GND. The transistor Q3 is for supplying a recording current 1o to the recording head section B, and its base is connected to the emitter of the transistor Q2, and its collector is connected to the power supply V. 0, respectively. The transistor Q4 also supplies the recording current I to the recording head section B. The base is connected to the emitter of the transistor Q1, the emitter is connected to the emitter of the transistor Q3, and the collector is connected to GND. The common emitter connection point of the transistors Q3 and 04 is connected to the recording head section B via a capacitor C.

The recording head section B is composed of a current limiting resistor R, a rotary transformer 3, and an 11-channel head 4. One end of one coil of rotary transformer 3 is connected to GND,
The other ends are each connected to a capacitor C via a current limiting paper RR. A magnetic head 4 is connected to the other coil of the rotary transformer 3. Recording signals are recorded on the video tape by the magnetic head 4.

FIG. 5 is a diagram showing current waveforms at various parts of the circuit of FIG. 4. Further, FIG. 6 shows an equivalent circuit of the recording head section B. In FIG.

Next, the operation will be explained using FIG. 5.

Assume that, for example, a sine wave voltage is input as a signal to be recorded to the input terminal 1. A signal input from input terminal 1 is transmitted to transistors Q3 .
Supplied to the base of Q4.

Transistor Q3 becomes conductive in response to the positive half wave of the sine wave voltage, and a current having a waveform as shown in FIG. 5(a) flows through transistor Q3. On the other hand, the transistor Q4 becomes conductive in response to the negative half wave of the sine wave voltage, and a current having a waveform as shown in FIG. 5(b) flows through the transistor Q4. Therefore, the recording current I is supplied from the output stage A to the recording head section B. As shown in FIG. 5(C), transistor Q3.
The current is a composite of the currents flowing through Q4.

The recording head section B receives the supplied recording current (■). Information is recorded on the video tape by the magnetic head 4 according to the size of the video tape. Here, the recording current I. The magnitude of is determined based on the equivalent circuit of the recording head section B shown in FIG. It becomes a resistance component.

(Problem to be solved by the invention) A conventional magnetic recording amplifier is configured as described above.
When the magnetic head 4 is used for a long time and becomes worn, the inductance component becomes smaller, and the recording current I applied to the recording head section 8 decreases as shown by equation (1).
. increases. Therefore, the frequency characteristics may change or V
When an audio signal is recorded in the deep part of a videotape and a video signal is recorded on top of it, as in the H8 Hi-Fi, the audio signal is recorded in the deep part of the videotape.
There was a problem in that the audio and video signals were mixed and interfered with each other.

This invention was made in order to solve the above-mentioned problems. Even if the impedance of the recording head changes, the recording current applied to the recording head does not change, and as a result, the frequency characteristics do not change. First, it is an object of the present invention to obtain a magnetic recording amplifier in which audio signals and video signals do not coexist in VH8 high-fidelity, and these signals do not interfere with each other.

[Means to solve the problem]

A magnetic recording amplifier according to the present invention includes a variable gain amplifier that receives a signal to be recorded and amplifies the signal, and a magnetic head, and the magnetic head records the signal amplified by the variable gain amplifier on a recording medium. a recording head section for controlling the recording head section, a monitor section for monitoring the recording current supplied from the variable gain amplifier to the recording head section, and a gain of the variable gain amplifier according to the magnitude of the recording current monitored by the monitor section. The configuration includes a control means for changing the recording current and keeping the recording current constant.

[Effect]

The monitor section in this invention monitors the recording current supplied from the variable gain amplifier to the recording head section, and the control means changes the gain of the variable gain 1W converter in accordance with the magnitude of the recording current monitored by the monitor section. This keeps the recording current constant regardless of changes in the impedance of the recording head.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of a magnetic recording amplifier according to the present invention. In the figure, the difference from the conventional example shown in FIG. 4 is that a variable gain amplifier 2a is used instead of the recording amplifier 2.
At the same time, the recording N given to the recording head section B
A monitor unit for monitoring the current 1o, and a gain control 11 according to the value of the recording current I0 monitored by this monitor unit, and variable gain amplification of the voltage 5a! 2a, and a level detector 5 that changes the gain of the variable gain amplifier 2 is newly installed.

The monitor part is NPN transistor Q5 and QB, PN
P transistors Q6 and Q7. Diodes D1 and D2
．． It consists of a monitor resistor R1.

Transistor Q5 has a base connected to the base of transistor Q3, and an emitter connected to transistor Q3. The collector connects the power supply ■c to the emitter common connection point of Q4 through the diode D1.
o, respectively. The transistor Q6 has a base connected to the base of the transistor Q4, an emitter connected to the emitter of the transistor Q5, and a collector connected to GND via the diode D2. Transistor Q7 is
The base is connected to the collector of the transistor Q5, and the emitter is connected to the power supply Vco. Transistor Q8 is
The base is the collector of transistor Q6, and the emitter is G
ND, the collectors of which are connected to the collector of transistor Q7.

A current flowing through the transistor Q3 is detected by a current mirror consisting of a transistor Q5, a diode D1, and a transistor Q7, and is applied to a monitoring resistor R1. Transistor Q6, diode D2 and transistor Q
74 current flowing through the transistor Q4 is detected by a current mirror consisting of 8, and is applied to the monitoring resistor R1. The monitor resistor R1 is connected to the collector of the transistor Q8 and G.
It is connected in series with a bias voltage source between ND and converts the applied current into voltage.

The level detector 5 is constituted by, for example, an envelope detector, detects the voltage generated in the monitoring resistor R1, and applies a gain control voltage 5a corresponding to the voltage value to the variable gain amplifier 2.
give to a. The variable gain amplifier 2a changes the gain according to the voltage value of the applied gain control voltage. Other configurations are the same as before.

Next, the operation will be explained. When a sine wave voltage is input to input terminal 1, transistor Q3. Current flowing through Q4 and recording current I. The waveform shown in FIG. 5 is the same as in the conventional case. In this case, the recording current I. If is a predetermined value, the gain control voltage 5a generated from the level detector 5 does not change. Therefore, the gain of the variable gain amplifier 2a does not change, and the feedback circuit for keeping the recording current I0 constant is in a stable state.

Next, a case where the inductance component of the recording head section B becomes smaller due to wear of the magnetic head 3 will be described. When the inductance component becomes smaller, the recording current I increases according to equation (1). increases. Then, the voltage generated across the monitoring resistor R1 increases, and the level detector 5 changes the gain control voltage 5a in response to this voltage change. In response, the gain of the variable gain amplifier 2a is lowered, and the amplitude of the waveform supplied to the output stage A becomes smaller. Therefore, transistor Q3. The current conductivity of Q4 is reduced, and the recording current I is supplied to the recording head section B. decreases. Then, when the voltage value detected by the level detector 5 reaches a predetermined value, the gain of the variable gain amplifier 2a becomes stable.

On the other hand, the impedance of the recording head section B increases for some reason, resulting in recording Ti flow I. When R decreases, the voltage generated across the monitoring resistor R decreases.

Then, level detection 2! In response to this voltage change, i5 changes the gain control voltage 5a in the direction of increasing the gain of the variable gain amplifier 2a. And variable gain amplifier 2a
The gain of A increases, and the amplitude of the waveform supplied to output stage A increases. Therefore, transistor Q3. The current conductivity of Q4 increases and the recording current I. increases. Also in this case, the gain of the variable gain amplifier 2a becomes stable when the voltage value detected by the level detector reaches the predetermined value.

As mentioned above, the recording current I is maintained regardless of the change in the impedance of the recording head section B. is kept constant, so there is no change in frequency characteristics, and even in the case of VH8 high-fidelity, audio and video signals do not mix and these signals do not interfere with each other. Furthermore, since the gain of the recording amplifier 2 can be varied depending on the magnitude of the recording Ti current, the current limiting resistor R4 used in the past becomes unnecessary.

In the circuits shown in FIGS. 1 and 4, the transistor Q
3. A large current flows through Q4. Generally, when a large current flows through a transistor, the current amplification factor hFE decreases, so to prevent this, the sizes of transistors Q3 and Q4 are made large. Therefore, transistor Q5. Q6 is a transistor Q3. If it is the same size as Q4, the circuit area will be large. However, transistor Q5. Change the emitter size of Q6 to transistor Q3. Even if Q4 is 1/N, transistor Q3. Q4 base
Emitter voltage and transistor Q5. It will be equal to that of Q6.

...(2) V: Voltage between base and emitter F of transistor k: Boltzmann constant T: Absolute temperature q: Amount of electric charge ■E: Emitter current I8: Saturation current Therefore, transistor Q5. Change the size of Q6 to transistor Q3. Even if it is 1/N of Q4, transistor Q3.
The current flowing through Q4 can be monitored. FIG. 2 shows transistor Q5. Change the size of Q6 to transistor Q3
．． It is a current waveform diagram of each part when it is set to 1/N of the size of Q4.

FIG. 3 is a diagram showing another embodiment of the present invention, showing another aspect of the monitor section. FIG. 3(a) shows the diode D2 and transistor Q6 in the embodiment shown in FIG.
．． Q8 is eliminated and the half-wave component of the recording current is monitored. FIG. 3(b) shows the diodes Di, D2, transistor Q6, . Q
7. Q8 is eliminated and a monitoring resistor R5 is connected to the collector of transistor Q5 to monitor the half-wave component of the recording current. These configurations also provide the same effects as those of the above embodiments.

Furthermore, in the embodiments shown in FIGS. 1 and 3, the recording current is monitored through the transistor Q5 or Q6, but the recording current (the current flowing through the transistors Q3 and Q4) may also be directly monitored. . In other words, transistor Q3. The collector current of Q4 may be monitored by the same method as in the above embodiment.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a monitor unit that monitors the recording current supplied from the variable gain amplifier to the recording head unit, and a monitor unit that controls the gain of the variable gain amplifier according to the magnitude of the recording current monitored by the monitor unit. Since a control means is provided to change the recording current and keep it constant, the recording current can be kept constant even if the impedance of the recording head changes, and as a result, the frequency characteristics do not change, making it possible to maintain the recording current constant even when the impedance of the recording head changes. does not mix audio and video signals,
The effect is that these signals do not interfere with each other.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a current waveform diagram showing the operation of the circuit in FIG. 1, FIG. 3 is a circuit diagram showing another embodiment of the invention, and FIG. 5 is a circuit diagram showing a conventional magnetic recording amplifier, FIG. 5 is a current waveform diagram showing the operation of the circuit of FIG. 4, and FIG. 6 is a diagram showing circuits of the recording head section of the magnetic recording amplifier. In the figure, 28 is a variable gain amplifier, 5 is a level detector, B is a recording head section, and D is a monitor section. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa Figure 5, Drawing subject to amendment Figure 4 6゜Contents of amendment

Claims (1)

[Claims] (1) a variable gain amplifier that receives a signal to be recorded and amplifies the signal; a recording head section that includes a magnetic head and records the signal amplified by the variable gain amplifier onto a recording medium by the magnetic head; a monitor unit that monitors the recording current supplied from the variable gain amplifier to the recording head unit; and a monitor unit that changes the gain of the variable gain amplifier according to the magnitude of the recording current monitored by the monitor unit, and A magnetic recording amplifier equipped with control means to maintain a constant value.