JPH0771259B2 - Magnetic reproducing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic reproducing apparatus, and more particularly, to a magnetic reproducing apparatus capable of adaptively controlling a noise removal amount included in a luminance signal according to a reproducing level. Regarding the device.

[Prior Art] FIG. 5 is a block diagram showing a reproducing circuit of a conventional video tape recorder (hereinafter referred to as VTR). Referring to FIG. 5, this reproducing circuit includes a head 16 for reproducing a signal recorded on a video tape 15, a head amplifier 17,
FM processing circuit 1 with FMAGC circuit 13 and FM equalizer 14
8, an FM demodulation circuit 19, a low-pass filter 20, a de-emphasis circuit 21, a noise canceller circuit 22c, a picture control circuit 23, and a chroma mixing circuit 24.

In operation, the signal is reproduced from the video tape 15 by the head 16, amplified by the signal head amplifier 17, and then given to the FM processing circuit 18. FMAGC provided in the FM processing circuit 18
The signal processed by circuit 13 and FM equalizer 14 is FM
It is given to the demodulation circuit 19. The signal demodulated by FM by the circuit 19 is supplied to the low-pass filter 20, and the baseband signal after the FM carrier component and unnecessary noise components are removed is supplied to the de-emphasis circuit 21. The output signal of the circuit 21 is given to the noise canceller circuit 22c, and the noise included in the luminance signal is removed by a predetermined noise cancel level. The signal from which the noise is removed by the circuit 22c is processed by the picture control circuit 23 and the chroma mixing circuit 24, and then output as a video signal.

[Problems to be Solved by the Invention] Generally, when a video tape is repeatedly reproduced, the level of the reproduction signal decreases due to the demagnetization effect, and therefore the reproduction signal
S / N ratio decreases. Therefore, conventionally, as shown in FIG. 5, a noise canceller circuit 22c is provided to remove a predetermined amount of noise. Generally, when a high quality video signal is obtained, it is desirable not to process the video signal by the noise canceller circuit. This is because the frequency characteristic is deteriorated by the action of the noise canceller circuit. However, in the conventional VTR, since the noise canceller circuit 22c for removing a predetermined amount of noise is applied as described above, even if a high quality video signal is obtained, the noise canceling process is uniformly performed. It was done. As a result, the frequency characteristic is deteriorated, and the resolution of the video that should be obtained by the high quality video signal is lowered.

The present invention has been made to solve the above problems, and provides a magnetic reproducing device capable of adaptively controlling the amount of noise removal included in a luminance signal according to the level of a reproducing signal. With the goal.

[Means for Solving the Problem] A magnetic reproducing apparatus according to the present invention includes a reproducing means for reproducing a video signal recorded on a magnetic tape, and a noise removing means for removing noise from a reproduced luminance signal. , Detecting means for detecting the demagnetization state of the magnetic tape in response to the level of a signal of a specific frequency contained in the reproduced FM video signal, and noise of the noise removed by the noise removing means in response to the output of the detecting means. Control means for controlling the quantity.

[Operation] In the magnetic reproducing apparatus according to the present invention, based on the level of the signal of the specific frequency included in the reproduced FM video signal,
The demagnetization state of the magnetic tape is detected by the detection means. The control means controls the amount of noise removed by the noise removal means according to the demagnetized state of the magnetic tape.

[Embodiment of the Invention] FIG. 1 is a circuit block diagram showing a reproducing circuit of a VTR showing an embodiment of the present invention. Referring to FIG. 1, this VT
R is a head 16 for reproducing a signal recorded on the video tape 15, a video amplifier 17, an FMAGC circuit and an F
An FM processing circuit 18 including an M equalizer, an FM demodulation circuit 19,
A low-pass filter 20, a de-emphasis circuit 21, a noise canceller circuit 22a, a reproduction level detection circuit 10 for detecting the level of a reproduction signal, a control circuit 11a for controlling the noise cancellation level of the noise canceller circuit 22a, and a picture. It includes a control circuit 23 and a chroma mixing circuit 24.

In operation, the reproduced signal is the de-emphasis circuit
Until it is processed by 21, the same processing as the conventional circuit shown in FIG. 5 is performed. On the other hand, the reproduction signal amplified by the head amplifier 17 is given to the reproduction level detection circuit 10.

FIG. 2 is a noise canceller circuit 22a shown in FIG.
6 is a waveform diagram for explaining the operation of FIG. Although various types of noise canceller circuits are generally known, an example thereof is shown in FIG. The video signal S1 input to the noise canceller circuit 22a is applied to the low-pass filter composed of the resistor 51 and the capacitor 5, and its output signal S2 is applied to the subtractor 52. Subtractor 52
Subtracts the signal S2 from the original video signal S1 and supplies the subtracted signal S3 to the limiter circuit 53. The output signal of the limiter circuit 53 is given to the subtractor 54, and the subtractor 54 outputs the signal S5 indicating the subtraction result of the signal S4 and the original video signal S1. The output signal S5 is given to the picture control circuit 23.

The noise canceller circuit 22a is characterized in that the noise cancel level is controlled in response to the level of the reproduction signal, as described below. That is,
The reproduction level is detected by the reproduction level detection count 10, and the noise cancellation level is controlled as follows in response to the detection result.

FIG. 3 is a circuit diagram showing an example of the reproduction level detection circuit 10 shown in FIG. Referring to FIG. 3, this reproduction level detection circuit outputs to the output of the amplification circuit unit 3 via the coupling circuit 47 and the amplification circuit unit 3 connected so as to receive the FM signal reproduced from the head amplifier 17. Connected integration circuit section 4 and comparison circuit section 5 connected to the output of integration circuit section 4
Including and

In operation, the reproduced FM signal is given to the base of the npn transistor 31 forming the first stage amplifier via the resistor 30. The low-frequency Coumaro signal component of the signal amplified by the transistor 31 is dropped to the ground through the series connection of the coil 32 and the capacitor 33. The signal from which the chroma signal component has been removed is given to the base of the npn transistor 34 which constitutes the second stage amplifier. The signal current-amplified by the transistor 34 is given to the base of the npn transistor 39 which constitutes the amplifier of the third stage via the coupling capacitor 36. At that time, the resistors 37 and 38 form a bias circuit. A collector peaking circuit 40 composed of a resistor, a capacitor and a coil is connected to the collector of the transistor 39, and this circuit 40 allows a sync chip level frequency (for example, about 3.4 MHz in the case of the VHS method).
Only the signal component of z) is further amplified. The output signal of the collector peaking circuit 40 is given to the integration circuit unit 4 via the capacitor 47.

An npn transistor 44 that constitutes an amplifier is provided in the integrating circuit unit 4.
And its bias resistors 41 and 42 are provided.
Resistors 41 and 42 bias the DC component of the base voltage applied to the base of transistor 44 near ground. As a result, the integration circuit section 4 rectifies the signal component of the sync tip level frequency in the reproduced FM signal and converts it into a DC voltage signal S9 indicating the reproduced level of the reproduced FM signal. The output signal S9 is the comparison circuit unit 5 connected to the next stage.
Given to.

The comparison circuit unit 5 includes resistors 61 and 62 for generating a reference voltage, and a comparator 63. The comparator 63 is
Its negative input is connected to receive signal S9 and its positive input is connected to receive the aforementioned reference voltage. The comparator 63 compares the voltage level of the signal S9 with the reference voltage, outputs the high level signal S8 when the voltage level of the signal S9 is lower than the reference voltage, and outputs the low level signal S8 when it is high.
Is output.

The control circuit 11a shown in FIG. 1 operates in response to this signal S8. That is, when the reproduced FM signal becomes equal to or lower than a predetermined level, a high level signal S8 is given, and the npn transistor 27 is turned on, so that the capacitor 28 is connected in parallel with the capacitor 5 in the noise canceller circuit 22a. As a result, the capacitance value forming the low-pass filter of the noise canceller circuit 22a is increased, and the noise cancellation level is increased. On the other hand, when the level of the reproduced FM signal is higher than the predetermined level, the transistor 27 is turned off, so that the capacitor 28 is not connected in parallel with the capacitor 5. Therefore, at this time, the noise cancellation level can be suppressed low.

Generally, by repeatedly reproducing a magnetic tape, its reproducing level is reduced by its demagnetizing effect. On the other hand, a tape that has not been reproduced so much can obtain a high reproduction level. In this case, a high-resolution image can be obtained without performing the noise canceling process. On the contrary, if the noise canceller process is performed, the resolution is rather lowered. When the reproducing circuit shown in FIG. 1 is used, the noise canceling level can be adaptively controlled according to the level of the reproducing signal, so that the noise canceller circuit 22a functions as necessary, and a high quality reproducing signal can be obtained. It is possible to prevent deterioration of the S / N ratio in the case of

FIG. 4 is a circuit block diagram showing a VTR reproducing circuit according to another embodiment of the present invention. In the noise canceller circuit 22b shown in FIG. 4, a capacitor 5 and a variable capacitance diode 91 which are connected in parallel with a capacitor 5 which constitutes a low pass filter are connected in series. Capacitor 90
Is a variable capacitance diode to block the DC component of the signal
Has a capacity value greater than 91. Variable capacitance diode 91
Has its capacitance value reduced in response to a high DC control voltage. Conversely, its capacitance value is increased in response to a low DC control voltage. That is, the capacitance value of the capacitor connected in parallel with the capacitor 5 can be changed according to the DC control voltage.

The output signal S9 of the integrating circuit section 4 in the reproduction level detecting circuit shown in FIG. 3 is given as the DC control voltage. This signal S9 indicates a change in the level of the reproduced FM signal as a change in DC voltage. By applying this signal S9 to the noise canceller circuit 22b shown in FIG. 4, the noise canceller level can be continuously controlled in response to the level of the reproduced FM signal.

As described above, according to the present invention, the control means for controlling the amount of noise removed from the luminance signal according to the demagnetization state of the magnetic tape is provided, and therefore the magnetic field that is not demagnetized A magnetic reproducing device capable of preventing the deterioration of the S / N ratio of the reproduced signal obtained from the tape was obtained.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a VTR reproducing circuit according to an embodiment of the present invention. FIG. 2 is a waveform diagram for explaining the operation of the noise canceller circuit shown in FIG. FIG. 3 is a circuit diagram showing an example of the reproduction level detecting circuit shown in FIG. FIG. 4 is a circuit block diagram showing a VTR reproducing circuit according to another embodiment of the present invention. FIG. 5 is a circuit block diagram showing a conventional VTR reproducing circuit. In the figure, 3 is an amplification circuit section, 4 is an integration circuit section, 5 is a comparison circuit section, 10 is a reproduction level detection circuit, 11a is a control circuit, and 2 is a control circuit.
2a, 22b and 22c are noise canceller circuits.

Claims (1)

[Claims] 1. A reproducing means for reproducing a video signal recorded on a magnetic tape, a noise removing means for removing noise from a luminance signal reproduced by the reproducing means, and an FM video signal reproduced by the reproducing means. In response to the level of the signal of the specific frequency included in the detection means for detecting the demagnetization state of the magnetic tape, and in response to the output of the detection means, the amount of noise removed by the noise removal means. A magnetic reproducing device including control means for controlling.