JPS6412026B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a magnetic recording device such as a VTR.

Generally, in a VTR, the brightness signal of the video signal to be recorded is boosted in the high range by a pre-emphasis circuit, and then the overshoot or undershoot that occurs in the rising and falling parts of this signal is clipped, and then FFM is applied. It is modulated and recorded on magnetic tape. As mentioned above, the reason why the high frequency range of the signal to be recorded is enhanced is because the higher the modulation frequency component of the FM modulated wave, the more susceptible it is to noise.
The high-frequency component is enhanced in advance, and the modulation degree for that frequency component is enhanced to reduce the influence of noise during FM demodulation and improve the S/N ratio.
The above-mentioned overshoot and undershoot occur in the pre-emphasis signal, and if this is input to the FM modulation circuit as it is, the frequency deviation will momentarily become large at the overshoot part.
There is a risk of overmodulation. Overmodulation causes an inversion phenomenon and S/N deterioration during reproduction, and a clip circuit is provided to prevent this.

Conventionally, as the above-mentioned pre-emphasis and clip circuits, those shown in FIGS. 1 and 2 are known. In the figure, resistors R ₁ , R ₂ , R ₃ and capacitor C ₁ determine the characteristics of the pre-emphasis, and the clip level is determined by VR ₁ . 1 is a pre-emphasis circuit, 2 is a clip circuit, terminal 3 receives the luminance signal of the video signal to be recorded, output terminal 4 outputs a pre-emphasized and clipped signal, and this signal is FM modulated. input to a device (not shown). In Figure 1 above, pre-emphasis circuit 1
A clip circuit 2 is provided on the output side of the
In this case, a clip circuit 2 is provided in the feedback loop of the pre-emphasis circuit 1.

In the circuit of FIG. 1, when the signal shown in FIG.
As shown in FIG. 3b, the high frequency range is enhanced by the
As shown in Figure c, this clipping action works linearly, so after playback, the FM demodulated and de-emphasized waveform will have smear as shown in Figure 3d.
Due to the lack of high frequencies, the playback screen becomes a blurred image. On the other hand, in the circuit shown in Fig. 2, the clip circuit 2
is provided in the feedback loop, the clip acts non-linearly, and even if demodulated and de-emphasized after reproduction, the occurrence of smear will be less noticeable than in the circuit of FIG. FIG. 4 shows this state, where a is the signal to terminal 3, b is the waveform when pre-emphasized, and c is the waveform when clipped, and the area of A is equal to that of B.
d shows the waveform after demodulation and de-emphasis.

However, in the configuration shown in Figure 2, as mentioned above, areas A and B are equal in the clipped waveform in Figure 4c, so there is still room to improve the smear of the demodulated de-emphasis waveform as shown in Figure 4d. ing.

The present invention provides a circuit that can further reduce smear than the circuit shown in FIG.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. In Figure 5, the same symbols as in Figures 1 and 2 indicate the same meanings (hereinafter, Figures 7 and 8).
(Same in figure). 2a, 2b are clip circuits, one of which is connected to the output side of the pre-emphasis circuit 1;
The other is placed in a feedback loop.

In this way, by providing the clipping circuit 2b in the feedback loop and clipping the pre-emphasis output which has undergone non-linear pre-emphasis with the clip circuit 2a which has a linear clipping effect,
A non-linear clip is obtained.

Furthermore, by changing the clip point (level) of the clip circuits 2a and 2b, the waveform of the clip output can be changed, so for example,
By setting the clip point of the clip circuit 2b lower than the clip point of the clip circuit 2a, the area removed by the clip circuit 2b becomes larger than the area removed by the clip circuit 2a, as shown in FIG. 6c. Therefore, in the conventional device shown in FIG. 2, the areas A and B are equal as shown in FIG. It gets narrower. Therefore, even if de-emphasis is applied after reproduction, the result will be as shown in Figure 6d, and the smear will be less noticeable than in the case of Figure 4d. Note that FIG. 6a shows terminal 3 in the circuit of FIG.
Figure 6b is the waveform after pre-emphasis, Figure 6c is the waveform after clipping, Figure 6d is the waveform demodulated and de-emphasized after reproduction, and in Figure 6, C is the waveform after pre-emphasis. The clip point by the circuit 2a, and the clip point by the clip circuit 2b are shown by d.

7 and 8 show other embodiments, in which a white clip 2a is used as the clip circuit.
-1, 2b-1 and Dark Clip 2a-2, 2b
-2 (FIG. 8 shows only 2a-2). VR ₂ is a variable resistor for adjusting the white clip point, and VR ₃ is a variable resistor for adjusting the dark clip point.

As is clear from the above explanation, according to the present invention, two clip circuits with different clip points are provided on the output side of the pre-emphasis circuit and in the feedback loop, which is different from the conventional clip circuit provided only in the feedback loop. Smear in the de-emphasis waveform after demodulation can be further reduced than with the circuit.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams showing conventional examples;
5 and 4 are waveform diagrams of various parts in FIGS. 1 and 2, respectively, FIG. 5 is a circuit diagram showing an embodiment of the present invention, FIG. 6 is a waveform diagram of various parts in FIG. 5, and FIG. 8 are circuit diagrams showing other different embodiments. 1... Pre-emphasis circuit, 2a, 2b...
Clip circuit, 3...input terminal, 4...output terminal.

Claims (1)

[Claims] 1. In a magnetic recording device that performs clip processing after high-frequency amplification of a signal to be recorded, and performs FM modulation to record the signal, a first clip circuit is provided in the feedback loop of the pre-emphasis circuit for high-frequency amplification,
A magnetic recording device characterized in that a second clip circuit is provided for clipping the output of the pre-emphasis circuit.