JPH0472281B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a magnetic recording/reproducing device using an operational amplifier circuit as a recording amplifier circuit. Conventional Structures and Their Problems In recent years, the price of integrated circuits has decreased dramatically and they have come to be widely used in consumer equipment. Integrated circuits are also frequently used in magnetic recording/reproducing devices in place of conventional circuits using individual transistors. Transistor 1 for obtaining the frequency characteristics of a recording amplifier circuit of a conventional magnetic recording and reproducing device is shown below.
The circuit configuration using a stone and an operational amplifier will be explained. In general, it is desirable for magnetic recording and reproducing devices to record and reproduce frequency characteristics that are flat up to high frequencies, but especially at high frequencies, there are many loss factors such as gear loss in the head and spacing loss with the tape. first to the recording current to compensate for
The structure is such that it has sharp peaking characteristics as shown in the figure. Figure 2 shows an example of a recording amplifier circuit conventionally used mainly in cassette decks. transistor
Bias resistors R ₂ and R ₁ are connected between the base of Q ₁ and ground and power supply Vcc, respectively, and a coupling capacitor C ₁ is connected between the base and signal input terminal 1. transistor
There is a collector resistor R ₃ between the collector of Q ₁ and the power supply Vcc.
is connected, and a series circuit of a resistor _R5 and a capacitor _C2 is connected between its collector and one terminal of the head 2. Furthermore, an emitter resistor R ₄ is connected between the emitter of the transistor Q ₁ and the ground, and a coil L ₁ is connected between the emitter and the ground.
A series circuit of resistor R ₆ and capacitor C ₃ is connected. In the above configuration, the bias resistance R ₁ ,
_R2 provides the necessary base bias for transistor _Q1 . The input signal is sent from terminal 1 to the transistor via coupling capacitor _C1 .
This transistor Q ₁ is supplied to the base of Q ₁
The voltage amplification factor at is roughly determined by the ratio of the collector load impedance to the emitter load impedance, and the collector resistance R ₃ is large at several tens of kilohms, and the impedance on the head 2 side is also set relatively high regardless of the frequency by the resistance R ₅ . Therefore, the above voltage amplification factor ultimately depends on the emitter load impedance. Among the elements connected between the emitter of transistor Q ₁ and ground, the series circuit of coil L ₁ , resistor R ₆ , and capacitor C ₃ has a frequency that can be easily calculated.

There is a resonance point in [Formula], and the reactance at that time shows the minimum value of only the resistance _R6 . Since the resistor _R6 is normally set to a value that is at least one order of magnitude smaller than the emitter resistor _R4 , the recording amplification circuit shown in Figure 2 ends up with the above f _p
The maximum voltage amplification factor is obtained at the frequency of . This f _p matches the peak frequency of the recording current characteristic shown in Fig. 1, and by adding some circuits to the circuit shown in Fig. 2, the structure is configured so that the characteristics shown in Fig. 1 are obtained as a whole. . Recently, integrated circuits have become rapidly cheaper, and each amplifier in a magnetic recording/reproducing device is increasingly constructed from an operational amplifier using an integrated circuit. FIG. 3 shows a circuit configuration when this operational amplifier is applied to a recording amplifier circuit. A coupling capacitor C ₄ is connected between the non-inverting input terminal 3 and the signal input terminal 1 of the operational amplifier circuit 5, and a resistor R ₉ is connected between the inverting input terminal 4 and the output terminal 6.
Further, a series circuit of a capacitor C ₆ and a resistor R ₈ and a series circuit of a capacitor C ₅ , a coil L ₂ and a resistor R ₇ are connected between the inverting input terminal 4 and the ground.
A series circuit consisting of a capacitor _C7 and a resistor _R10 is connected between the output terminal 6 and the head 2. In the circuit shown in Fig. 3, the capacitor C ₅ ,
Near the resonant frequency fo of the series resonant circuit formed by the coil L ₂ and the resistor R ₇ , assuming that the resistor R ₇ is sufficiently smaller than the resistor R ₈ , the ratio of the signal voltage applied to the input signal terminal 1 and the signal voltage at the output terminal 6, that is, the voltage Amplification factor G
teeth But here, that's why becomes. Further, in a frequency range not affected by the series resonant circuit, the voltage amplification factor G is expressed by the following equation. G≒1+R ₉ /R ₈ The conventional examples shown in Figures 2 and 3 explained above both utilize the series resonance characteristics of a coil and a capacitor, but the coil has a large volume compared to the resistor and capacitor. However, the cost is high, which is a major drawback for low-to-intermediate equipment or equipment that requires miniaturization. On the other hand, as a method for obtaining sensitive frequency characteristics without using a coil, there is a conventional high-order active filter constructed using an operational amplifier circuit. Figure 4 shows a conventionally used inverting active filter type recording amplifier circuit, in which a series circuit consisting of a resistor _R11 and a capacitor _C9 is connected between the signal input terminal 1 and the inverting input terminal 4 of the operational amplifier circuit 5. A resistor R ₁₂ is connected between the node 7 and the ground, and a capacitor C ₈ is connected between the node 7 and the output terminal 6. Further, a resistor R ₁₃ is connected between the inverting input terminal 4 and the output terminal 6. Non-inverting input terminal 3 is connected to ground. In the circuit of FIG. 4, the resistors R ₁ ,
The currents flowing in the direction of the arrows R ₁₂ and R ₁₃ are respectively
When i ₁ , i ₂ , and i ₃ , the following equation holds true. Note that S is a Laplace operator. R ₁₂ i ₂ = i ₃ /SC ₉ R ₁₃ i ₃ = −V ₀ R ₁₁ i ₁ +i ₃ /SC ₉ = V _1N R ₁₂ i ₂ −1/SC ₈ (i ₁ −i ₂ −i ₃ )= From _V0 and above, the transfer characteristic of this recording amplification circuit is expressed by the following equation. V ₀ /V _1N = −SR ₁₂ R ₁₃ C ₉ /S ² R ₁₁ R ₁₂ R ₁₃ C ₈ C ₉ −S
R ₁₁ R ₁₂ (C ₈ + C ₉ ) + R ₁₁ R ₁₂ When calculating the frequency characteristics, becomes. From the above formula, the peak frequency f ₀ of this recording amplification circuit is
teeth becomes. The frequency characteristics of this recording amplifier circuit are shown in Figure 5, and as can be understood from the transfer function, the gain approaches zero in the low and high frequencies, and the need for stable gain in the middle and low frequencies. Not suitable for recording amplification circuits. Furthermore, even if other amplifier circuit parts are integrated into an integrated circuit, resistors can be incorporated on the chip in integrated circuits, but capacitors cannot be incorporated except for those of very small value. All parts other than R ₁₃ have to be external parts. Another drawback is that the input impedance of the circuit in Figure 4 has frequency characteristics due to capacitors _C8 and _C9 , and when each constant is determined so that the peak frequency fo mentioned above is the desired frequency, this The problem is that the input impedance cannot always be set to a desired value. Purpose of the Invention The present invention combines a capacitor and a resistor with an operational amplifier circuit without using a bulky and expensive coil, thereby obtaining the desired frequency characteristics and setting the input impedance to a constant value regardless of the frequency. The present invention provides a recording amplification circuit having a simple and completely new configuration in which a part of the resistor that determines the frequency characteristics can be formed on the same integrated circuit when it is integrated into an integrated circuit. Structure of the Invention The present invention applies a signal input to a non-inverting input terminal of an operational amplifier circuit, connects a first capacitor to the inverting input terminal, and connects a second capacitor to the output terminal, and A first resistor is connected between the connecting point and the ground, a second resistor is connected between the output terminal and the inverting input terminal, and a first resistor is connected between the first capacitor and the first resistor. A third resistor is connected in parallel to a series circuit of resistors, and the head is driven by the output from the output terminal. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 6 to 8. First, in FIG. 6, a resistor _R16 is connected between the output terminal 6 and the inverting input terminal 4 of the operational amplifier circuit 5, and a capacitor is connected between the output terminal 6 and the connection point 8.
C ₁₂ is connected, a capacitor C ₁₁ is connected between the node 8 and the inverting input terminal 4, and the inverting input terminal 4
Resistors R ₁₄ and R ₁₅ are connected between and ground, respectively. A coupling capacitor C ₁₀ is connected between the signal input terminal 1 and the non-inverting input terminal 3, and the non-inverting input terminal 3 is connected to a bias power supply E _B (not shown) via a resistor R ₁₈ . Output terminal 6
A series circuit consisting of a resistor _R17 and a capacitor _C13 is connected between the head 2 and the head 2. In FIG. 6, if the current i ₄ flowing in the direction of the arrow in the resistor R ₁₆ and the currents flowing in the capacitors C ₁₁ and C ₁₂ are respectively i ₆ and i ₅ , the following equation holds true. In addition, S
is the Laplace operator. R ₁₆ i ₄ =V ₀ -V _1N R ₁₆ i ₄ =i ₅ /SC ₁₂ +i ₆ /SC ₁₁ R ₁₄ (i ₄ +i ₆ ) =V _1N R ₁₅ (i ₅ -i ₆ ) +i ₅ /SC ₆ =V From _the above four equations, the transfer characteristic of this recording amplifier circuit is expressed by the following equation. Vo/V _1N = S ² R ₁₄ R ₁₅ R ₁₆ C ₁₁ C ₁₂ +S {(R ₁₅ R ₁₆ + R ₁₄ R ₁₆ +
R ₁₄ R ₁₅ ) C ₁₁ + R ₁₅ (R ₁₄ + R ₁₆ ) C ₁₁ + R ₁₄ + R ₁₆ /R ₁₄ {S ²
R ₁₅ R ₁₆ C ₁₁ C ₁₂ +SR ₁₅ (C ₁₁ +C ₁₂ )+1} Therefore, the frequency characteristics can be expressed as follows. From the above formula, the peak frequency f _p can be expressed as follows. Although the operational amplifier circuit 5 is shown as a black box in FIG. 6, in reality, a circuit such as the one shown in FIG. 7 is used as an integrated circuit. That is, in a differential amplification stage consisting of PNP transistors Q ₂ and Q ₃ having a common emitter, the base of transistor Q ₂ is connected to the non-inverting input terminal 3 and one end of resistor R ₁₈ . The other end of resistor _R18 is connected to voltage source E _B. The base of the transistor Q ₃ is connected to the inverting input terminal 4, and a resistor R ₁₄ , which is one element forming the feedback circuit explained in FIG. 6, is connected between the inverting input terminal 4 and the ground. A resistor R ₁₆ is connected between the input terminal 4 and the output terminal 6. The collector of transistor Q ₂ is connected to the collector and base of the NPN transistor and to the base of NPN transistor Q ₅ . The collector of transistor Q ₃ is connected to the collector of transistor Q ₅ and the base of NPN transistor Q ₆ . Note that a current source I ₁ is provided between the emitters of the transistors Q ₂ and Q ₃ and the power supply Vcc. power supply
Between Vcc and the collector of transistor Q ₆ is a current source I ₂
and diodes D ₁ and D ₂ are connected in series in this order. Regarding the output section, the emitter of the PNP transistor _Q7 is connected to the power supply Vcc, the base is connected to the anode of the diode _D1 , and the collector is connected to the output terminal 6 via a resistor _R19 . The base of the NPN transistor Q ₈ is connected to the collector of the transistor Q ₆ , which is connected to the output terminal 6 via a resistor R ₂₀ . Transistors Q ₄ , Q ₅ , Q ₆ ,
The emitters of Q ₈ are each connected to ground. The part within the dotted line in FIG. 7 is an integrated circuit, and the rest are external parts. In other words, a sampling capacitor C 10 is provided between the signal input terminal 1 and the non-inverting input terminal 3, and a sampling capacitor C ₁₀ is provided between the inverting input terminal 4 and the coupling point 8.
A capacitor C ₁₁ is connected between them, and a capacitor C ₁₂ is connected between the coupling point 8 and the output terminal 6. And there is a resistance between connection point 8 and ground.
R ₁₅ is connected. In the circuit shown in FIG. 7 above, the transistors Q ₂ ,
Q ₃ Q ₄ and Q ₅ are differential amplifier circuits, voltage source E _B provides the necessary bias voltage via resistor R ₁₈ , and the input impedance is the value of resistor R ₁₈ . Transistor _Q6 is the second amplification stage.
Current source _I2 is supplying idling current to the output circuit. Transistors Q ₇ and Q ₈ are output transistors. This circuit operates exactly the same as the circuit in Figure 6, and the resistor _R14 in Figure 6 is
In Figure 7, _R16 can be provided within the integrated circuit, and the external components used to determine the peak characteristics are resistors.
There are only three points: R ₁₅ , capacitors C ₁₁ and C ₁₂ . Figure 8 shows the above circuit, R ₁₄ = 12KΩ,
The frequency characteristics of the voltage gain are shown when R ₁₅ = 1KΩ, R ₁₆ = 19KΩ, and C ₁₁ =C ₁₂ = 3.9NF, and with these constants, the peak frequency fo = 9.36KHz. Further, at low frequencies, the gain of the conventional circuit shown in FIG. 5 approaches zero, whereas in FIG. 8, the value is G=1+R ₁₆ /R ₁₄ , and a sufficient gain is provided. Effects of the Invention As described above, according to the present invention, even if the series resonant coil used in the conventional circuit is abolished, the same voltage gain and frequency characteristics as the conventional circuit can be obtained, and it is several times higher than that of a capacitor or resistor. By eliminating the coil, the device can be made smaller and lower in price. In addition, if the circuit system according to the present invention is adopted in a situation where integrated circuits have been actively implemented in recent years, two of the five circuit elements that determine the peak frequency characteristics of voltage gain will be removed within the integrated circuit. As a result, the circuit configuration is simple with only three external components, two capacitors and one resistor, and therefore the assembly is simple, which is very effective.

[Brief explanation of the drawing]

Figure 1 is a frequency characteristic diagram of a general recording amplifier circuit of a magnetic recording/reproducing device, Figures 2, 3, and 4 are diagrams showing conventional recording amplifier circuits, respectively, and Figure 5 is the same as Figure 4. FIG. 6 is a block circuit diagram showing an embodiment of the present invention, FIG. 7 is a circuit diagram of the same, and FIG. 8 is a frequency characteristic diagram of the same circuit. 1... Signal input terminal, 2... Head, 3... Non-inverting input terminal, 4... Inverting input terminal, 5... Operational amplifier circuit, 6... Output terminal, _R15 , _R16 ... Resistor,
C ₁₁ , C ₁₂ ... Capacitor.

Claims (1)

[Claims] 1. Applying a signal input to a non-inverting input terminal of an operational amplifier circuit, connecting one terminal of a first capacitor to the inverting input terminal, and connecting one terminal of a second capacitor to the output terminal of the operational amplifier circuit, The other terminals of the first and second capacitors are coupled together, a first resistor is connected between the coupling point and ground, and a second resistor is further connected between the output terminal and the inverting input terminal, and A third resistor is connected in parallel to the series circuit of the first capacitor and the first resistor, and the arithmetic circuit, the second resistor, and the third resistor are formed as part of an integrated circuit; The first resistor, the first capacitor, and the second capacitor are configured as external components connected to the integrated circuit, and the head is driven by the output from the output terminal. Magnetic recording and reproducing device.