JP2689786B2 - Crosstalk reduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosstalk reducing circuit effective for use as a crosstalk reducing means in a rotating cylinder of a magnetic recording / reproducing apparatus.

[0002]

2. Description of the Related Art In recent years, the number of heads used in magnetic recording / reproducing apparatuses, particularly household video tape recorders and video cameras integrated with a camera, has been increasing in order to achieve high image quality and high sound quality.

On the other hand, there is a strong demand for miniaturization of equipment as a market trend, and there are restrictions on the magnetic recording system, so that the shape of the rotary cylinder cannot be made large.

Since the number of heads increases and the shapes are equal or smaller, crosstalk in the rotary transformer in the rotary cylinder is deteriorated.

The conventional means for improving the deterioration of crosstalk will be described below. FIG. 7A shows a conventional head,
It is a block diagram of a rotary transformer and a preamplifier.
Reference numerals 6 and 11 denote first-stage amplifiers of the preamplifier, 7 and 12 feedback amplifiers, 8 a signal switching circuit, 13 an output terminal thereof, and 14 an integrated circuit in recent years. Reference numerals 4 and 10 are terminals for setting the amount of negative feedback by the capacitors C3 and C5 and resistors R4 and R5. Reference numerals 5 and 9 are signal input terminals. C1 and C4 are coupling capacitors. L _H-1 and L _H-2 are head inductances, L _R-1 and L _R-2 are rotary side inductances of the rotary transformer, and L _S-1 and L _S-2 are fixed side inductances of the rotary transformer. Show.

FIG. 7A shows a block for two channels, but since each channel is the same, one channel will be briefly described.

A signal received by the head from the tape is amplified by a first stage amplifier 6 via a rotary transformer, a coupling capacitor C1 and an input terminal 5. This signal is amplified by the feedback amplifier 7 and supplied to the signal switching circuit 8 and is negatively fed back to the first stage amplifier 6 via R6 to stabilize the operation.

FIG. 7B is an equivalent circuit diagram obtained by simplifying FIG. 7A for the purpose of explanation. R _Z1 and R _Z2 are terminals 5 and 5, respectively.
Equivalent impedance seen from 6, L1 and L2 are heads,
This is the equivalent inductance including the rotary transformer.

It is already known that when the desired signal is received on the L2 side and the unnecessary signal is received on the L1 side, the amount of crosstalk from the L1 side to the L2 side is reduced by lowering the impedance of R _Z1. Conventionally, it is used as shown in FIG. 4 or FIG.

In the example of FIG. 4, as a means for lowering the impedance of R _Z1 , the saturation resistance of the transistor is in parallel by applying a control voltage from the terminal 1 to the transistor Q1. Although the operation is the same in the example of FIG. 6, a time constant circuit is provided by the resistor R3 and the capacitor C2 in order to compensate for the drawback of the example of FIG. 4 described below.

[0011]

However, the above-mentioned conventional structure has a performance problem of recording switch noise in the example of FIG. When a control voltage is applied to the terminal 1 of FIG. 4 at the timing as shown in FIG. 5A, the transistor Q1 is turned on, and a transient current of an amount close to the normal recording current flows as shown in FIG. 5B. When this switch noise current flows, it is recorded on the tape, which is not preferable. FIG.
In the example, since the voltage applied to the terminal 1 is applied to the transistor Q1 via the time constant circuit of R3 and C2 to moderate the impedance change of the transistor, there is no problem of recording the switch noise as described above. But,
This time constant requires a resistance value of about 10 to 100 KΩ and a capacitance value of about 0.01 μF to 1 μF, and since it is not a capacitance value that can be built in an integrated circuit, it has a problem that it must be used as an integrated circuit peripheral component. Was there.

The present invention solves the above conventional problems at the same time, and an object of the present invention is to provide a crosstalk reducing circuit which has a small switch noise current and is suitable for integration into an integrated circuit.

[0013]

To achieve this object, a crosstalk reducing circuit of the present invention connects the collector of a first transistor to the input of a preamplifier of a magnetic recording / reproducing apparatus and grounds the emitter. connects the first control signal obtained by delaying the second control signal to the base, and a pre-switch circuit
To the collector of the second transistor is connected to the input of the preamplifier via a resistor, the emitter grounded, the base
It has a configuration in which a second control signal is connected.

[0014]

With this configuration, the transistor is first turned on, but since it is through the resistor, the impedance does not change suddenly and the switch noise current is small. After that, the transistor is turned on by the delayed control signal to sufficiently reduce the impedance, so that the crosstalk can be reduced.

[0015]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, L1 is an equivalent inductance including a head and a rotary transformer, C1 is a coupling capacitor, R _Z is an equivalent impedance of a preamplifier,
The collector of the first transistor Q1 is connected to the input of the preamplifier, the emitter is grounded, the base is connected to the control signal 1 delayed from the control signal 2, and the second transistor Q2 is connected.
Is connected to the input of the preamplifier via a resistor R1, the emitter is grounded and the control signal 2 is connected to the base.

The operation of the crosstalk reducing circuit configured as described above will be described with reference to FIG. First,
A control signal 2 as shown in FIG. 2 (a) is applied from the terminal 2 to turn on the transistor Q2, but since it is via the resistor R1, a rapid impedance change does not occur and a switch noise current as shown in FIG. 2 (b) is obtained. FIG. 5B in the case of the circuit example of FIG.
Compared with the switch noise current of (3), it is significantly reduced and it is at a level that does not pose a problem. Next, by adding the control signal 1 obtained by delaying the control signal 2 as shown in FIG. 2 (c) to the base of the transistor Q1 to turn it on and sufficiently lower the impedance, crosstalk can be reduced. Note that Q1 is O
The switch noise current when N is set is as shown in FIG. 2 (d), which is at a level with no problem.

The delay amount from the control signal 2 to the control signal 1 uses a mono-multi circuit or a recent video tape recorder uses a microcomputer, and the control signals 1 and 2 can be supplied from this microcomputer. Omit details. The example in Fig. 2 is about 100μSEC, R
1 = 500Ω, Q1 saturation resistance is about 5Ω.

As described above, according to this embodiment, the transistor Q1 can sufficiently lower the impedance to reduce the crosstalk, and at the same time, the Q2 is pre-switched via the resistor R1 prior to the Q1. It is possible to provide a crosstalk reduction circuit that can suppress abrupt changes, suppress generation of a switch noise current, which is a conventional problem, and that is suitable for integration into an integrated circuit.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a crosstalk reducing circuit showing a second embodiment of the present invention. In FIG. 3, reference numeral 3 is a control signal input terminal, Q3 is a third transistor whose base is connected to the terminal 3, whose emitter is grounded and whose collector is connected to the input of the preamplifier through the resistor R2. , Q3, R
The configuration is the same as that of the first embodiment (FIG. 1) except that 2 is added.

The timing of the control signals 1, 2, and 3 may be 2 earlier than the control signal 1 and 3 earlier than 2. For example, the control signal 3 is delayed to form the control signal 2, and the control signal 2 is delayed. Then, the control signal 1 may be created and used.

The difference between the second embodiment and the first embodiment is that the impedance change can be made gentler than the first embodiment.
The point is that the switch noise currents of FIGS. 2B and 2D can be further reduced. By increasing the system of transistors and resistors in this way, it is possible to further reduce the switch noise current.

[0024]

As described above, according to the present invention, the collector of the first transistor is connected to the input of the preamplifier, the emitter is grounded, and the second control signal is delayed at the base .
Control signal is connected, the collector of the second transistor is connected as a pre-switch circuit to the input of the preamplifier through a resistor, the emitter is grounded, and the second control signal is applied to the base.
By providing the connected configuration, it is possible to realize a crosstalk reduction circuit suitable for an integrated circuit with a small switch noise current.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a crosstalk reduction circuit according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the crosstalk reduction circuit in the first embodiment.

FIG. 3 is a circuit diagram of a crosstalk reduction circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional crosstalk reduction circuit.

FIG. 5 is a waveform diagram for explaining a conventional crosstalk reduction circuit.

FIG. 6 is a circuit diagram of a second embodiment of a conventional crosstalk reduction circuit.

FIG. 7 is a block diagram for explaining a conventional crosstalk reduction circuit.

[Explanation of symbols]

 Q1, Q2 transistor R1 resistance

Claims (1)

(57) [Claims] 1. A collector of a first transistor is connected to an input of a preamplifier of a magnetic recording and reproducing apparatus, an emitter is grounded, and a first control signal obtained by delaying a second control signal is connected to a base, As the pre-switch circuit, the collector of the second transistor is connected to the input of the preamplifier via a resistor,
The emitter grounded, crosstalk reduction circuit comprising the arrangement for connecting the second control signal to the base.