JPH07320202A - Regenerative amplifier for magnetic head - Google Patents

Abstract

PURPOSE:To incorporate a capacitor by reducing capacitance value of the capacitor being a component of damping circuit deciding frequency characteristic of amplifier circuit in a reproducing amplifier device for magnetic head integrated on a semiconductor substrate. CONSTITUTION:The damping circuit 6 negatively feeds back a regenerative signal to the input of the amplifier circuit 4 amplifying the regenerative signal of magnetic head, and damps resonance characteristic by the inductance of the magnetic head and an input capacitor. Further, a low band frequency-pass filter is provided in the input part of a first gm device 13 in the damping circuit 6, and a DC component is amplified, and an AC component is amplified mainly by a second gm device 14, and the circuit 6 adds respective amplified output signals to feed back them negatively. The resistance value, the capacitance value of the low band frequency-pass filter are set independently of setting a gain, and the whole circuit incorporating the capacitor necessary for the damping circuit 6 is integrated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing / amplifying device for a magnetic head, and more particularly to a damping means.

[0002]

2. Description of the Related Art Conventionally, a reproducing / amplifying device for a magnetic head
(Hereinafter, referred to as a reproduction / amplification device), a reproduction / amplification device that amplifies the reproduction signal because the reproduction signal reproduced from the magnetic tape through the magnetic head has resonance characteristics due to the inductance and input capacitance of the magnetic head. Are required to correct the resonance characteristics. Therefore, the reproducing / amplifying device negatively feeds back the signal amplified by the amplifying circuit and the signal amplified by the amplifying circuit to the input end of the amplifying circuit, and resonates between the inductance and the input capacitance of the magnetic head. It is a commonly used method to configure a damping circuit for damping the characteristics to correct the resonance characteristics.

In the following, regarding the reproducing / amplifying device, a VHS of the VHS (registered trademark) standard is taken as an example, and FIG.
Will be described with reference to the schematic block diagram of FIG.

In FIG. 3, reference numeral 1 is a magnetic head, and a reproduction signal reproduced by the magnetic head 1 is transferred to a reproducing / amplifying device 4 through a rotary transformer 2, a shield wire 3 and a coupling capacitor C1 for switching a plurality of magnetic heads. Supplied on input. Here, C2 is a capacitor for resonance frequency adjustment (hereinafter referred to as resonance adjustment), and is input by a parallel circuit of the capacitance between the shielded wire 3 to ground and the resonance adjustment capacitor C2 and the parasitic input capacitance of the regenerative amplifier 4. Capacity is determined. At this time, the resonance frequency fo is formed by the combined inductance of the magnetic head 1 and the rotary transformer 2 and the input capacitance.

In the VHS standard VTR, the carrier frequency of the FM luminance signal is set from 3.4 MHz to 4.4 MHz.
By adjusting the capacitance value of the resonance adjusting capacitor C2, the value of the resonance frequency fo is set to a value near the white peak frequency of the FM luminance signal, that is, a value near 5 MHz to 6 MHz.

FIG. 4 is a frequency characteristic diagram of the regenerative amplifier.
Shows frequency characteristics without damping, and 8 shows frequency characteristics with damping. The output signal of the amplifier circuit 5 shown in FIG. 3 is supplied to the damping circuit 6 in response to the reproduction signal having the frequency characteristic 7 shown in FIG. 4 without damping, and the external resistor R1 and the external capacitor C are supplied.
The amount of feedback is made variable by 3, and the amount of damping is adjusted. Then, by performing negative feedback to the input terminal of the amplifier circuit 5 via the feedback resistor R2, as shown in the frequency characteristic 8 with damping in FIG. 4, the regenerative amplifier device 4 having a flat frequency characteristic up to around 5 MHz is configured. It is a common method. In this case, assuming that the gain of the negative feedback loop is A, an equivalent resistance having an equivalent resistance value of (R2 / A) is formed in parallel with the resonance circuit formed by the magnetic head inductance and the input capacitance. The amount of damping can be adjusted by the gain A of the loop.

Next, a conventional reproducing / amplifying device is shown in FIG.
And it demonstrates using FIG. FIG. 5 is a block diagram showing a circuit configuration of a conventional regenerative amplifier device, and FIG. 6 is an example of a specific circuit thereof. Here, components having the same operation and effect described in FIG. Detailed description is omitted. In FIG. 5, 9 is a voltage controlled current output amplifier
(Hereinafter, referred to as gm device), 10 is a first voltage source for generating a reference voltage at the input of the gm device 9, 11 is a second voltage source connected to the output of the gm device 9 via a resistor R3, 12 Is a buffer circuit.

Further, the output of the gm device 9 is connected to the resistor R1 and the buffer circuit 12. At this time, one end of the resistor R1 is grounded via the capacitor C3, and
Since one end of the resistor R3 is connected to the second voltage source 11, the gain of the output of the voltage-converted gm device 9 is
The transconductance value (hereinafter referred to as gm value) of gm
1. Gain of DC component (hereinafter referred to as DC gain) is G (D
C), the gain of the AC component (hereinafter referred to as AC gain) is G (A
C)

[0009]

[Formula 1] G (DC) = gm1 × R3

[0010]

[Formula 2] G (AC) = gm1 × (R1 // R3) A signal having a DC gain G (DC) amplified to (Formula 1) and an AC gain G (AC) amplified to (Formula 2). But the buffer circuit 12
And is fed to the input of the amplifier circuit via the feedback resistor R2.

The DC component is supplied to the amplifier circuit 5 as a bias of the input transistor and is negatively fed back so that the average output voltage of the amplifier circuit 5 becomes equal to the voltage value of the first voltage source 10. Therefore, in order to solve the problem of offset voltage and the like, a larger value is generally required for the DC gain G (DC).

Further, the AC component is negatively fed back to the input of the amplifier circuit 5 for damping the reproduction signal from the magnetic head 1. As is well known, the reproduction signal from the magnetic head 1 is extremely weak, so that the AC gain G (AC) of the damping circuit 6 forming the negative feedback path is required to have a considerably small value. For this reason,

[0013]

[Expression 3] R1 << R3 (Expression 3) is set, and the AC gain G (AC) is

[0014]

Equation 4 G (AC) = gm1 × R1 (Equation 4)

Next, in FIG. 6 showing an example of the concrete circuit of FIG. 5, Q1 is an input transistor, and transistors Q2 and Q3, diodes D1 to D3, and resistors R4 to R are provided.
A cascode type amplifying circuit 5 is constructed together with 6. The transistors Q4 and Q5 form a differential amplifier circuit,
The gm device 9 is configured with the transistors Q6 and Q7 that configure the current mirror circuit. Also, the diodes D4, D
5, the resistor R14 constitutes the second voltage source 11, and the transistor Q8 and the resistor R15 constitute the buffer circuit 12.

[0016]

However, in the configuration of the conventional example described above, a sufficiently large DC gain G (DC) and a considerably small AC gain G (AC) are required, while on the other hand, in the damping circuit. Since the AC gain G (AC) and the DC gain G (DC) are set by one gm unit, the resistance value of the resistor R3 for setting the DC gain G (DC) and the AC gain The resistance value of the resistor R1 for setting G (AC) cannot be set irrespectively, and the capacitance value of the capacitor C3 for grounding one end of the resistor R1 in alternating current is also set independently of the resistors R1 and R3. However, it has a drawback that the circuit design becomes complicated.

Further, it is practical that the resistance value which can be integrated in the semiconductor substrate is in the range of 100Ω to 100 kΩ.
Even if 3 is set to the maximum resistance value of 100 kΩ, the resistance R1 is set to 1
It must be set to about kΩ, and the capacitor C3 connected in series with the resistor R1 needs to have a large capacitance value of 0.1 μF or more so that the impedance can be ignored compared to the value of the resistor R1. However, the capacitance value that can be integrated is 100 pF or less, and it is impossible to integrate a large capacitance of 0.1 μF. From this, conventionally, when such a reproducing / amplifying device 4 is integrated in a semiconductor integrated circuit, it is necessary to provide the external terminal T2 so that the capacitor C3 can be externally attached, and the external amplifying device T2 is housed in a larger package. However, mounting is performed using a large peripheral component (capacitor), which causes a problem in that the mounting area on the printed circuit board becomes large and the cost is reduced.

The present invention solves the above-mentioned problems of the prior art, in which a DC gain G (DC) and an AC gain G (AC) can be set individually, and a capacitor C for determining the AC gain G (AC).
It is possible to reduce the capacitance value of 3. Therefore, it is an object of the present invention to provide a regenerative amplifier device in which the circuit design is facilitated and the conventionally externally attached capacitor C3 can be incorporated in an integrated circuit.

[0019]

In order to achieve this object, the present invention provides an amplifier circuit for amplifying a reproduction signal of a magnetic head, and an output signal of the amplifier circuit, which is negatively fed back to an input end of the magnetic head. A reproducing circuit for a magnetic head, which comprises a damping circuit for damping the resonance characteristic between the inductance and the input capacitance of the magnetic head, the damping circuit comprising: a first signal for amplifying a DC component of an output signal of the amplifying circuit. A processing circuit; and a second signal processing circuit that amplifies mainly the AC component of the output signal of the amplification circuit,
It is characterized in that the output signals of the first and second signal processing circuits are added and negatively fed back to the input end of the amplifier circuit.

Further, the damping circuit has a low-pass frequency pass filter consisting of a resistor and a capacitor in its input section, and a first signal processing circuit for amplifying an output signal of the amplifier circuit by comparing it with a reference potential, A second signal processing circuit for amplifying mainly an alternating-current component of the output signal of the amplifier circuit, adding each output signal of the first and second signal processing circuits, and negatively feeding back to the input end of the amplifier circuit. It is characterized by doing.

The first signal processing circuit comprises a differential amplifier circuit which has a capacitor between the input and output and which amplifies the output signal of the amplifier circuit by comparing it with a reference potential.

[0022]

According to the above construction, the output signal of the amplifier circuit is first
DC signal is amplified by the signal processing circuit and the AC signal is amplified by the second signal processing circuit. Since the output signals that have been individually amplified are added and negatively fed back to the input end of the amplifier circuit, the DC feedback amount and the AC feedback amount of the negative feedback loop can be set arbitrarily, and the output voltage offset is stabilized, The damping of the frequency characteristic of the amplifier circuit can be adjusted individually.

By providing the low-pass frequency pass filter at the input section of the first signal processing circuit, the values of the resistor and the capacitor forming the low-pass frequency pass filter can be set independently of the gain setting, and the resistance value can be set. It is possible to increase the capacitance and decrease the capacitance value. Further, the DC negative feedback amount and the AC negative feedback amount can be set individually, and the output voltage of the amplifier circuit can be set in accordance with the reference potential.

Since the capacitor for the low-frequency pass filter is connected between the input and output of the differential amplification circuit in the first signal processing circuit, the equivalent capacitance difference due to the Miller effect is the gain of the differential amplification circuit. Even if the capacitance value of the capacitor composing the low pass filter is small, the DC component of the output signal of the amplifier circuit can be sufficiently extracted, and the capacitor in the damping circuit can be integrated in the semiconductor substrate. it can.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a detailed description of the embodiments of the regenerative amplifier according to the present invention with reference to the drawings. Also, the same reference numerals are given to those having the same action and effect described in FIGS. 5 and 6 of the conventional example, and the detailed description thereof will be omitted.

FIG. 1 is a block diagram showing the circuit configuration of the regenerative amplifier device of this embodiment, and FIG. 2 is an example of a specific circuit thereof. In FIG. 1, 13 is a first gm device (first signal processing circuit), 14 is a second gm device (second signal processing circuit), and 15 is a first and second gm device 13, 14. A first voltage source 16 for generating a reference input voltage, 16 is a gm device 13 via a resistor R18.
The second voltage sources 17 and 18 connected to the output of the buffer circuit are buffer circuits.

The output of the first gm device 13 is connected to the buffer circuit 17, and the output of the buffer circuit 17 is connected to the buffer circuit 18 via the resistor R19. And the first gm
Since the input portion of the device 13 is provided with a low-pass frequency pass filter composed of a resistor R16 and a capacitor C4, the first gm device 13 is supplied with the DC component of the output signal of the amplifier circuit 5. The direct current component and the alternating current component of the output signal of the amplifier circuit 5 are supplied to the second gm device 14.

Therefore, the voltage-converted first gm device
The gain of the output of 13 is the gm value of the first gm device 13, gm2,
If the DC gain of the first gm device 13 is G (DC1),

[0029]

G (DC1) = gm2 × R18 This DC component is supplied as the bias of the input transistor in the amplifier circuit 5 through the feedback resistor R2, the resistor R19, and the buffer circuits 17 and 18, and the average of the amplifier circuit 5 is obtained. Negative feedback is performed so that the output voltage becomes equal to the voltage value of the first voltage source 15.

The gain of the voltage-converted output of the second gm device 14 is gm3 of the second gm device 14 and gm3 is the second gm value.
If the DC gain of the m unit 14 is G (DC2) and the AC gain is G (AC),

[0031]

[Equation 6] G (DC2) = gm3 × R19

[0032]

## EQU7 ## G (AC) = gm3 × R19 One end of the resistor R19 is connected to the first gm via the buffer circuit 17.
The second DC gain G (DC2) shown in (Equation 6) and the first DC gain G shown in (Equation 5) because they are connected to the output of the device 13.
The gain obtained by adding (DC1) becomes the total DC gain G (DC) of the entire damping circuit 6, and the AC gain G (AC) shown in (Equation 7) becomes the AC gain of the entire damping circuit 6.

Then, this output signal is transferred to the buffer circuit 18,
Also, negative feedback is performed to the input terminal of the amplifier circuit 5 via the feedback resistor R2. As described in the conventional example, in order to solve the problems such as the offset voltage, the DC gain G (DC) is required to have a larger value and the AC gain G (AC) is required to have a considerably smaller value. It may be set so as to satisfy the expression (8).

[0034]

[Equation 8] R19 << R18 In the present embodiment, the low-frequency pass filter (composed of the resistor R16 and the capacitor C4) is used as the first gm device 13
Since it is provided in the input part of, considering only the cutoff frequency of the low pass filter, regardless of the gain setting,
It is sufficient to determine the values of the resistor R16 and the capacitor C4, which facilitates circuit design. In addition, the first gm device 13 is the first voltage source
Since the reference potential given from 15 and the output voltage of the amplifier circuit 5 are compared and DC-amplified and negatively fed back to the input end of the amplifier circuit 5, the output voltage of the amplifier circuit 5 can be set according to the reference potential. , The DC negative feedback amount is set by the gain of the first gm device 13, and the AC negative feedback amount is set by the gain of the second gm device 14.

Resistor R that constitutes a low pass filter
As for the resistance value of 16 and the capacitance value of capacitor C4,
Since the low-pass frequency pass filter is provided at the input part of the first gm device 13, each value can be selected regardless of the gain setting. If the resistance R16 is set to the maximum resistance value (100 kΩ) that can be integrated, as compared with the case where the AC amplification cutoff frequency is determined between the resistance R1 (1 kΩ) and the capacitor C3 in the conventional example shown in FIG. It is also possible to set the value of the capacitor C4 to about 1/100. However, even in this case, in the conventional example, C3 is 0.1 μF, whereas C4 is reduced to a capacitance value of 1000 pF.
It is still difficult to integrate 4 into a semiconductor integrated circuit. However, even if the capacitor C4 is externally attached, there are sufficient advantages such as a smaller shape and a lower cost if the capacitance value becomes smaller.

The resistor R17 in the circuit shown in FIG.
The resistance value of the resistor R16 keeps the balance of the voltage drop due to the input current of the first gm device 13, and even if the input current increases, the average output voltage of the amplifier circuit 5 is the reference voltage of the first voltage source 15. It is designed so as to follow, and is not always necessary.

Next, an example of a circuit in which the value of the capacitor C4 can be further reduced in the concrete circuit of FIG. 1 will be described with reference to FIG. In FIG. 2, Q1 is an input transistor, and transistors Q2 and Q3, diodes D1 to D3,
A cascode type amplifier circuit 5 is configured with R4 to R6,
These are the same as the configuration of the conventional example. Transistor Q
A first differential amplifier circuit is constituted by 9 and Q10, and a first gm device 13 is constituted together with the transistors Q11 and Q12 which constitute the first current mirror circuit. Also, the transistor Q
A second differential amplifier circuit is constituted by 13 and Q14, and a second gm device 14 is constituted by the transistors Q15 and Q16 which constitute the second current mirror circuit.

The second voltage source 16 is composed of the diodes D6 to D8 and the resistor R32, and the transistor Q17
With the resistor R33, the buffer circuit 17 is connected to the transistor Q18.
And the resistor R34 form a buffer circuit 18. A resistor R16 and a capacitor C4 form a low pass filter, and the capacitor C4 is a base of the transistor Q9.
It is configured to be connected between collectors (between the input and output of the first gm device 13).

When the circuit is constructed in this way, the DC gain G
Since the capacitor C4 is connected between the input and output of the first gm device 13 having a sufficiently large (DC), the capacitor C4 and the first gm device 13 that form the low-pass frequency pass filter function as a mirror capacitance. The capacitance value is equivalent to the gain of the first gm device 13, that is, (gm2 × R18) times the equivalent capacitance.
Therefore, if the gain of the first gm device 13 is 100 times,
The equivalent capacitance is 00 times, and as shown in the block diagram of FIG. 1, compared with the case where the capacitor C4 is connected to the ground point,
The value of the added capacitor can be reduced to 1/100,
It may be possible to integrate all regenerative amplifier circuits 4 including the capacitor C4.

[0040]

As described above, in the reproducing / amplifying apparatus for a magnetic head of the present invention, the first signal processing circuit performs DC amplification, the second signal processing circuit performs AC amplification, and the individually amplified output signals. Is added to perform negative feedback to the input end of the amplifier circuit, the DC feedback amount of the negative feedback loop and the AC feedback amount can be set individually and individually, and the adjustment of the output offset of the amplifier circuit and the damping amount of the frequency characteristic is performed. Can be done individually, which facilitates circuit design.

Further, when the low-pass frequency pass filter is provided in the input section of the first signal processing circuit, it becomes possible to use a resistor having a large value regardless of the gain setting, and the low-pass frequency pass filter can be used. It is possible to reduce the capacitance value of the capacitors to be configured, and if the capacitors are used to configure a Miller integrating circuit, it is possible to integrate all circuits including the capacitors required for the damping circuit. Has the effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a magnetic head reproducing / amplifying device according to an embodiment of the present invention.

FIG. 2 is a specific circuit diagram of a magnetic head reproducing / amplifying device according to an embodiment of the present invention.

FIG. 3 is a schematic block diagram showing a basic configuration of a conventional magnetic head reproducing / amplifying device.

FIG. 4 is a frequency characteristic diagram of (7) no damping and (8) damping of a conventional magnetic head reproducing / amplifying device.

FIG. 5 is a block diagram showing a circuit configuration of a conventional magnetic head reproducing / amplifying device.

FIG. 6 is a specific circuit diagram of a conventional magnetic head reproducing / amplifying device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic head, 2 ... Rotary transformer, 3 ... Shielded wire, 4 ... Regenerative amplifier, 5 ... Amplifier circuit, 6
... damping circuit, 7 ... frequency characteristic without damping, 8 ... frequency characteristic with damping, 9 ... gm
, 10, 15 ... First voltage source, 11, 16 ... Second voltage source, 12, 17, 18 ... Buffer circuit, 13 ... First gm device
(First signal processing circuit), 14 ... Second gm device (second signal processing circuit), T1, T2 ... External terminals, Q1-Q18 ...
Transistors, D1 to D8 ... Diodes, R1 to R
34 ... Resistor, C1 ... Coupling capacitor, C2 ... Resonance frequency adjusting capacitor, C4 ... Low pass filter capacitor.

Claims (3)

[Claims] 1. An amplifier circuit for amplifying a reproduction signal of a magnetic head, and an output signal of the amplifier circuit is negatively fed back to an input end,
In a magnetic head reproduction / amplification device including a damping circuit for damping a resonance characteristic between an inductance and an input capacitance of the magnetic head, the damping circuit amplifies a DC component of an output signal of the amplifier circuit. No. 1 signal processing circuit and a second signal processing circuit for amplifying mainly the AC component of the output signal of the amplifier circuit, and adding the output signals of the first and second signal processing circuits to amplify the output signal. A reproducing / amplifying device for a magnetic head, characterized by negatively feeding back to an input end of a circuit. 2. An amplifier circuit for amplifying a reproduction signal of a magnetic head, and an output signal of the amplifier circuit is negatively fed back to an input end,
In a magnetic head reproducing / amplifying device including a damping circuit for damping a resonance characteristic between an inductance and an input capacitance of the magnetic head, the damping circuit includes a low-pass frequency pass filter including a resistor and a capacitor as an input unit. And a first signal processing circuit that amplifies the output signal of the amplifier circuit by comparing it with a reference potential, and a second signal processing circuit that amplifies mainly the AC component of the output signal of the amplifier circuit, A reproducing / amplifying device for a magnetic head, wherein the output signals of the first and second signal processing circuits are added and negatively fed back to the input end of the amplifying circuit. 3. The first signal processing circuit comprises a differential amplifier circuit which has a capacitor between input and output and which amplifies the output signal of the amplifier circuit by comparing it with a reference potential. Item 2. A reproducing / amplifying device for a magnetic head according to item 2.