JPH07244805A - Reproduction input amplification circuit and vtr - Google Patents

Abstract

PURPOSE:To increase the bandwidth of frequency characteristics by changing the phase of a feedback signal according to the frequency within the range of negative feedback. CONSTITUTION:A negative feedback path 6 consists of a feedback amplifier, a feedback resistor 8, and a phase rotation circuit 9. The phase rotation circuit 9 consists of a series circuit of a capacitor C2 and a resistor R2 and the impedance of the capacitor C2 decreases as the frequency of the reproduction input signal increases, thus also reducing the impedance of the rotation circuit 9. Therefore, those bypassed to the ground increase among amount of feedback and the amount of negative feedback to the input of a reproduction input amplifier 3 decreases, thus equivalently decreasing the capacity of an input capacitor C1. It means that the phase of the negative feedback path 6 was rotated to the positive side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing input amplifier circuit used in a magnetic recording / reproducing apparatus such as a VTR.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional reproducing input amplifier circuit. In FIG. 5, 50 is a reproducing magnetic head, L ₁ is its head coil, 51 is a DC blocking capacitor, 52 is a reproducing input amplifier, and 53 is a reproducing input amplifier. Output terminal, 54 is a feedback amplifier 55
And a feedback resistor 56 is a negative feedback path.

As is well known, the frequency characteristic of this type of reproduction input amplifier circuit is determined by the head coil L ₁ and the input capacitance C ₁ . The peaking of the frequency characteristic formed by L ₁ and C ₁ is flattened by applying negative feedback to the reproduction input amplifier 52. However, if the amount of negative feedback is increased, the input capacitance C ₁ becomes equivalently large, and the peak of the frequency characteristic shifts to the low frequency side.

In a VTR (video tape recorder), the image quality cannot be improved unless the high frequency range is extended. Therefore, in Japanese Examined Patent Publication No. 5-74123, a positive feedback path is provided separately from the negative feedback path to equivalently reduce the capacitance of the input capacitance C ₁ .

[0005]

However, the method of Japanese Patent Publication No. 5-74123 has a drawback that the circuit becomes complicated because two system paths are required as the return path of the reproduction input amplifier. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a regenerative input amplifier circuit having a wide frequency characteristic band, although only a negative feedback path is used as a feedback path. .

[0006]

To achieve the above object, in the reproducing input amplifier circuit of the present invention, the frequency of the reproducing signal is increased in the negative feedback path of the reproducing input amplifier for amplifying the reproducing signal of the magnetic head coil. Accordingly, a means for reducing the amount of negative feedback is provided.

[0007]

According to this structure, the amount of negative feedback is reduced at high frequencies, so the input capacitance is equivalently reduced, and peaking due to the magnetic head coil and the input capacitance is increased to the high frequency side. It shifts and the high frequency side of the frequency characteristic extends. Although the equivalent reduction of the input capacitance is equivalent to the positive feedback provided separately from the negative feedback, the present invention can be realized with only one feedback path. That is, in the present invention, in the negative feedback path, the phase of the feedback signal changes (rotates) according to the frequency within the range of the negative feedback.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments shown in the drawings will be described below. In FIG. 1 in which the present invention is implemented, 1 is a magnetic head,
L ₁ is its head coil, 2 is a DC blocking capacitor, C ₁
Is an input capacitance, 3 is an input reproduction amplifier, 4 is an output terminal, and 6 is a negative feedback path composed of a feedback amplifier 7, a feedback resistor 8 and a phase rotation circuit 9.

The phase rotation circuit 9 is composed of a series circuit of a capacitor C ₂ and a resistor R ₂ . When the frequency of the reproduction input signal increases, the impedance of the capacitor C ₂ decreases, and the impedance of the phase rotation circuit 9 also decreases. Therefore, a large amount of the negative feedback amount is bypassed to the ground, the negative feedback amount to the input of the reproduction input amplifier 3 is reduced, and the capacitance of the input capacitance C ₁ is equivalently reduced.
This means that the phase of the negative feedback path 6 has rotated to the positive side. In other words, the amount of positive feedback has increased (however, it is negative feedback as a whole, and the amount of positive feedback does not exceed the amount of negative feedback).

FIG. 2 shows frequency characteristics, (a) shows the conventional example shown in FIG. 5, and (b) shows the case according to the present embodiment of FIG. As described above, according to the present embodiment, the high frequency band is extended, and a wide band reproduction signal can be dealt with correspondingly.

FIG. 3 shows a concrete configuration of FIG. 1. The reproduction input amplifier 3 is composed of transistors Q1 to Q6 and its associated circuit elements, and the feedback amplifier 7 is transistors Q8 to Q16 and its associated circuit elements. It is composed of.

A phase rotation circuit 9 consisting of a series circuit of a capacitor C ₂ and a resistor R ₂ has one end connected to a signal line from the collector connection point of the transistors Q8 and Q10 to the base of the transistor Q14, and the other end connected to the ground. ing. The transistors Q8 to Q13 in the feedback amplifier 7 represent a differential amplifier circuit, and the transistors Q14 to Q16 form a buffer.

By using the reproduction input amplifier circuit of this embodiment described above, the reproduction band can be expanded without impairing the performance of the magnetic head. That is, the performance of the magnetic head is evaluated by improving the reproduction output (improving the S / N ratio) and increasing the resonance frequency. However, if the output is only increased, the head chip width may be increased, The number of turns of the coil may be increased. However, increasing the chip width of the head and increasing the number of turns of the coil both increase the inductance of the coil, so the resonance point due to the inductance of the coil and the input capacitance is lowered, and the reproduction characteristics in the high range are increased. Is damaged. On the contrary, if the chip width of the head is reduced or the number of turns of the coil is reduced in order to improve the reproduction characteristic in the high frequency range, the output of the head is reduced. However, when the reproduction input amplifier circuit of this embodiment is used, the high frequency characteristic can be improved while keeping the head output large.

FIG. 4 shows a case where the reproduction input amplifier circuit is used for a VTR. Reference numeral 53 represents a magnetic tape. The playback input amplifier circuit is shown at 54. Luminance signal circuits 55 to 61 and chrominance signal circuits 62 to 66 are connected to the output side of the reproduction input amplifier circuit 54, and the luminance signal and the chrominance signal are individually processed.
The signals are synthesized by the adder 67 and given to the video processing circuit 68. Since these circuits are well known, the description thereof will be omitted.
As described above, when the reproduction input amplifier circuit of the present embodiment is used for a VTR, wide band, improvement of resolution, improvement of S / N ratio, etc. are achieved, and a high image quality VTR can be realized.

[0015]

As described above, according to the reproducing input amplifier circuit of the present invention, the reproducing band can be expanded without deteriorating the performance (reproducing output) of the magnetic head. Further, when this reproduction input amplifier circuit is used for a VTR, a wide band, improvement in resolution, improvement in S / N ratio, etc. are achieved and a high quality VTR is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a reproduction input amplifier circuit embodying the present invention.

FIG. 2 is a diagram showing the frequency characteristic thereof.

FIG. 3 is a circuit diagram specifically showing the configuration of FIG.

FIG. 4 is a circuit diagram of a main part of a VTR equipped with the reproduction input amplifier circuit.

FIG. 5 is a diagram showing a configuration of a conventional reproduction input amplifier circuit.

[Explanation of symbols]

 1 magnetic head device 3 reproduction input amplifier 6 negative feedback path 7 feedback amplifier 8 feedback resistor 9 phase rotation circuit

Claims (3)

[Claims] 1. A reproduction input amplifier circuit comprising means for reducing a negative feedback amount as the frequency of the reproduction signal increases in a negative feedback path of a reproduction input amplifier for amplifying a reproduction signal of a magnetic head coil. . 2. The regenerative input amplifier circuit according to claim 1, wherein the means is a series circuit of a capacitor and a resistor connected between the negative feedback path and the ground. 3. A video tape recorder using the reproduction input amplifier circuit according to claim 1 or 2.