JPH05128410A - Crosstalk reduction circuit - Google Patents

Abstract

PURPOSE:To provide a crosstalk reduction circuit with small switching noise current and suitable for integrated circuit, in order to reduce crosstalk in a rotary transformer of a magnetic recording/reproducing device. CONSTITUTION:A collector of 1st transistor Q1 is connected to the input of a preamplifier of the magnetic recording/reproducing device, and an emitter is grounded, then a control signal 1 making a control signal 2 delay is connected to a base. Then, the crosstalk reduction circuit is obtained by constituting it in such a manner that a collector of 2nd transistor Q2 is connected to the input of preamplifier through a resistor R1 and an emitter is grounded and the control signal 2 is connected to a base.

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, the 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 initial amplifiers of the preamplifier, 7 and 12 are feedback amplifiers, 8 is a signal switching circuit, 13 is an output terminal thereof, and 14 is a portion which has been integrated into a 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, only one channel will be briefly described.

A signal received by the head from the tape is amplified by the first stage amplifier 6 via the rotary transformer, the coupling capacitor C1 and the 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 configuration 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 a quantity 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. See also 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 into 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 an integrated circuit.

[0013]

To achieve this object, the crosstalk reducing circuit of the present invention connects the collector of the first transistor to the input of the preamplifier of the magnetic recording / reproducing apparatus and grounds the emitter. , A control signal obtained by delaying the control signal 2 is connected to the base, the collector of the second transistor is connected to the input of the preamplifier through a resistor, the emitter is grounded, and the control signal is connected to the base. ing.

[0014]

With this structure, the transistor is first turned on, but since it is connected 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】

(First Embodiment) 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 the resistor R1 is used, a sudden 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, it is greatly reduced and it is at a level where there is no problem. Next, by adding the control signal 1 obtained by delaying the control signal 2 as shown in FIG. 2C 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. 2D, which is at a level without any 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. In the example of Fig. 2, the delay amount 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 the Q2 can be 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, 3 is a control signal input terminal, Q3 is a third transistor whose base is connected to terminal 3, whose emitter is grounded and whose collector is connected to the input of the preamplifier through 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 number of transistors and resistors in this way, the switch noise current can be further reduced.

[0024]

As described above, according to the present invention, the collector of the transistor is connected to the input of the preamplifier, the emitter is grounded, the control signal 1 delayed from the control signal 2 is added to the base, and the preswitch is used. By connecting the collector of the transistor to the input of the preamplifier through a resistor, grounding the emitter, and adding a control signal to the base, a crosstalk reduction circuit suitable for integrated circuits with less switch noise current can be provided. It can be realized.

[Brief description of 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 reducing 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 (2)

[Claims] 1. A pre-switch in which a collector of a first transistor is connected to an input of a preamplifier of a magnetic recording / reproducing apparatus, an emitter is grounded, and a first control signal obtained by delaying a control signal 2 is connected to a base. A crosstalk reducing circuit comprising a circuit in which a collector of a second transistor is connected to an input of a preamplifier through a resistor, an emitter is grounded, and a second control signal is connected to a base. 2. The crosstalk reducing circuit according to claim 1, wherein a plurality of preswitch circuits are provided.