JPH0659016B2 - Magnetic head read signal amplification circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit, and more specifically, it reads a control signal written in a control track of a magnetic tape or the like with a magnetic head and reproduces it. The present invention relates to an improvement of an amplifier circuit in a magnetic head read circuit capable of reducing a noise component and accurately extracting a control signal or the like in the magnetic head read circuit.

[Prior Art] Conventionally, in a video recording / reproducing device (VTR) and the like,
A video signal is recorded on the video track, and a control signal is written on the control track.
The control signal is used to control the capstan servo system. For example, when the video signal is reproduced, the control head is positioned on the control track and is read out, and the video head scans the recorded track correctly and is good. It is used for control to reproduce various signals.

The magnetic head read circuit that reproduces the control signal is
There is a case where a window pulse is generated at a predetermined timing, a read waveform extracted in accordance with the window pulse is amplified, pulsed by a waveform shaping circuit, and taken out. The amplifier circuit is
Normally, a gate circuit is inserted on the input side, and the input signal (read waveform signal of the magnetic head) is selectively amplified according to the timing of the gate signal.

[Problems to be Solved] As described above, in the amplifier circuit having the gate circuit on the input side, the input signal is cut while the gate is closed (“OFF”), but the amplifier circuit is It remains in the amplification state regardless of the gate operation. Therefore, noise corresponding to the gain appears on the output side of the amplifier circuit including the noise generated inside the amplifier circuit even during the period when the gate is "OFF". In particular, in the amplifier circuit provided in the read circuit of the magnetic head, the gain is set to a high value of, for example, several tens of dB to 100 dB, so that the circuit at the next stage is a waveform shaping circuit using a comparator or the like. In the case of the waveform pulsing circuit, the output noise of the amplification circuit is input to the comparator or the level judgment circuit, which affects the judgment level, which may cause erroneous detection or malfunction. Become.

In the read circuit of the magnetic head described above, when the gate is in the "OFF" state, the signal level drops to the negative side, that is, a zag (drooping phenomenon) occurs, which is amplified in the "OFF" period. May appear on the output side and adversely affect the subsequent comparator or level determination circuit.

The present invention solves the above-mentioned problems of the prior art, and provides an amplifier circuit in which unnecessary signals are not generated at the output of the amplifier circuit during the gate closed period (hereinafter referred to as the gate "OFF" period). The purpose is to

[Means for Solving the Problems] The structure of the magnetic head read signal amplifying circuit of the present invention for achieving the above object includes: a gate circuit for receiving a read signal from a magnetic head generated at a predetermined cycle; An amplifier that receives the output of the gate circuit, a window pulse generation circuit that receives the output signal of the amplifier, generates a window pulse for opening the gate circuit to extract the next read signal, and sends the window pulse to the gate circuit, A gain reducing circuit that generates an inverted signal of a window pulse and reduces the gain of the amplifier in a period other than the window period in response to the inverted signal is generated.

[Operation] As described above, by providing the gain reducing circuit and suppressing the unnecessary output signal by decreasing the gain of the amplifier circuit during the gate “OFF” period according to the gate signal, the gate is turned off. In this state, the noise level is reduced during unnecessary periods of operation to prevent unnecessary signals from being input to the circuits in the subsequent stages, thereby preventing malfunction of the circuits in the subsequent stages and processing the input signals at an accurate level. It allows you to do things.

By the way, when a signal is read from a magnetic medium by the magnetic head, noise generated by the magnetic head traveling on the magnetic medium gives a sound quality, an image, and the like. The circuit in the subsequent stage is likely to malfunction due to noise.

However, in the present invention, since there is the above-mentioned action,
When amplifying a read signal from the magnetic head generated in a predetermined cycle such as a control signal, not only noise in the period other than the read signal can be reduced, but also in the present invention, an inverted signal of the window pulse is generated. Accordingly, the gain of the amplifier received from the gate circuit is reduced during the period other than the window period, so that it is possible to reduce the switching noise of the gate circuit, which largely affects the subsequent circuit as the noise. .

[Embodiment] An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a magnetic head read circuit of an embodiment to which the amplifier circuit of the present invention is applied.

In the figure, 1 is a magnetic tape set in a VTR, and 1a is a control track in which a control signal is written as a 30 Hz pulse signal, for example. 2 is a control head (hereinafter referred to as a magnetic head) for reading a control signal from the control track 1a.
And the write pulse signal of 30 Hz is applied to the magnetic tape 1
Are read in response to the scanning of the magnetic head 2 with respect to.

The control signal read by the magnetic head 2 is cut into a DC component as an analog signal by the capacitor 3, and is input to the operational amplifier (OP) 5 via the gate circuit 4. This read signal is amplified by the operational amplifier 5 during the period in which the gate circuit 4 is “ON”, input to the comparator (COM) 6, shaped into a pulse signal, and output to the output terminal 10.

The control signal read and reproduced by the magnetic head 2 in this manner is output from the comparator 6 and is used as a signal for controlling the position where the video head scans the magnetic tape 1 or the like, or is supplied to various other circuits. And is used as a control signal.

At this time, the output pulse signal of the comparator 6 is also input to the timing generation circuit 7. The timing generation circuit 7 receives the output pulse signal of the comparator 6, generates a window pulse for extracting the read signal of the magnetic head 2 at a predetermined timing in response to the pulse signal, and supplies it to the gate circuit 4 as the next gate signal. To do.

That is, since the window pulse becomes the next gate signal, if the control signal is first input, the entire circuit operates. The gate circuit 4 is normally closed because it is a normally closed switch as indicated by the switch symbol. It will open when receiving a signal from the outside. Therefore, if the first control signal is read from the magnetic head 2,
A signal is input to the operational amplifier 5 via the gate circuit 4, its output is applied to the timing generation circuit 7 via the comparator 6, and a window pulse is generated at a predetermined timing with respect to the control signal to be read next,
This window pulse causes the gate circuit 4 to be closed ("ON") by cutting the signal for the window period, and the next control signal is extracted during this window period. With this control signal, the next window pulse is sequentially generated in the same manner.

Now, the gain of the operational amplifier 5 here is controlled according to the gate signal. The operational amplifier 5 is
This is a non-inverting type amplifier, and in order to control the amplification factor, a switch circuit 8 is inserted in parallel with a feedback resistor Rf that determines the amplification factor. Here, the switch circuit 8 is normally open because it is a normally open switch as indicated by the switch symbol. Closed when receiving a signal from the outside. The switching control of the switch circuit 8 is performed according to the output signal of the inverter 9 which receives the gate signal. Therefore, the operation of the switch circuit 8 is in the period opposite to that of the gate circuit 4. That is, during the gate open period with a gate signal (hereinafter referred to as the gate “ON” period), “OF” is set.
F ", and it is turned" ON "in the gate" OFF "period when there is no gate signal.

As described above, the switch circuit 8 is turned “ON” during the period other than the gate “ON” period, so that the input side and the output side of the operational amplifier 5 are short-circuited during this period, and the operational amplifier 5 is
The gain of 1 drops to about 1 during this period. Therefore, the operational amplifier 5 operates as a buffer and the output voltage thereof is fixed to the bias voltage on the input side. As a result, during the period in which the gate circuit 4 is “OFF”, a stable level signal with almost no noise appears at the output of the operational amplifier 5.

The resistor Rs and the capacitor C are a bias circuit inserted in series between the reference level input side of the operational amplifier 5 and the ground. Further, the gate circuit 4, the switch circuit 8 and the like, for example, an analog switch circuit is used, and the magnetic head read circuit as a whole is formed into an IC by using an IC that can be integrated with the operational amplifier 5, the inverter 9 and the like. You can

As described below, in this embodiment, the operational amplifier is used to short-circuit the input side and the output side to reduce the gain to about 1. However, the present invention is not limited to such a case where the gain is greatly reduced. However, even if noise is transmitted to the subsequent stage, it is sufficient to reduce the gain to the extent that it does not have an adverse effect.
Therefore, a resistor having a certain resistance value may be inserted in series with the switch circuit 8, and the connection form is not limited to that in the embodiment.

In the embodiment, the control is performed so that the gain of the amplifier circuit is reduced by the inverter and the switch circuit.
The reduction of the gain of the amplifier circuit is not limited to such means,
For example, various gain reducing means such as reducing the power supply voltage of the operational amplifier can be used, and the circuit is not limited to the circuit shown in the embodiment.

[Effects of the Invention] As can be understood from the above description, in the present invention, the gain reduction circuit is provided to reduce the gain of the amplification circuit during the gate "OFF" period in accordance with the gate signal. By suppressing unnecessary output signals, the gate becomes “O”.
Since the noise level is reduced during the operation-unnecessary period in the "FF" state so that an unnecessary signal is not input to the circuit in the subsequent stage, the subsequent circuit is less likely to malfunction and the input signal is processed at an accurate level. can do.

Moreover, since the inverted signal of the window pulse is generated and the gain of the amplifier received from the gate circuit during the period other than the window period is reduced accordingly, the switching noise of the gate circuit can also be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a magnetic head read circuit of an embodiment to which the amplifier circuit of the present invention is applied. 1 ... magnetic tape, 1a ... control track, 2
... magnetic head, 4 gate circuit, 5 operational amplifier, 6 comparator, 7 timing generator, 8 switch circuit, 9 inverter.

Claims (1)

[Claims] 1. A gate circuit for receiving a read signal from a magnetic head generated at a predetermined cycle, an amplifier for receiving an output of the gate circuit, and a next read signal for receiving the output signal of the amplifier. A window pulse generating circuit for generating a window pulse for opening the gate circuit and sending it to the gate circuit, and an inversion signal of the window pulse for generating a gain of the amplifier in a period other than the window period. And a gain reduction circuit for reducing the magnetic head read signal amplification circuit.