JPS60140932A - Pre-emphasis circuit - Google Patents

Abstract

PURPOSE:To suppress the reduction in response especially at 1-2MHz by using two high pass filters with different cut-off frequency and synthesizing high frequency component obtained from each filter. CONSTITUTION:The 1st high pass filter 21 selected to the 1st cut-off frequency f1 and the 2nd high pass filter 25 using a frequency f2 higher than the frequency f1 as a cut-off frequency are provided, the 2nd high frequency component Yl2 obtained from them is applied to a synthesizer 23, where they are added. The 1st cut-off frequency f1 is selected in this example to 880kHz and the 2nd cut-off frequency f2 is selected to nearly 1.6MHz. Moreover, in this example the frequency response is increased by 4-6dB at the frequency band of 1-2MHz. Thus, the frequency band of 1-2MHz is emphasized sufficiently in the overall frequency characteristic of a pre-emphasis circuit 20 and the frequency characteristic after noise cancel is as shown in Curve l0 so as to suppress the deterioration of response near 1-2MHz.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a no-emphasis circuit suitable for application to the recording system of a VTR. A noise canceling circuit is usually provided to remove it from the reproduced luminance signal. The frequency characteristic of the noise canceling circuit is such that the subcarrier frequency becomes zero near 3.58 MHz, as shown by curve t in FIG.

As is clear from this frequency characteristic, noise cancellation processing affects the high-frequency components of the luminance signal, especially the resolution.2. Since even a few components near OMHzMHz are dropped, fine parts become blurred as a reproduced image, and only an image with significantly degraded resolution can be obtained.

In order to eliminate this drawback, conventionally, a luminance signal recording system is provided with a serial emphasis circuit for emphasizing the high-frequency components of the luminance signal.

FIG. 1 shows an example of such a case. In this recording system, the color video signal supplied to the terminal (1) is separated into a luminance signal Y and a carrier color signal C by the Y/C separation circuit (2), and the luminance signal Y is sent to the AGO circuit (3). , flange circuit (5)
The signal is then supplied to the FM modulator (7) via a pre-emphasis circuit (6) having a linear frequency characteristic and subjected to FM modulation.

The carrier color signal C is supplied to the frequency converter α° C. via the ice circuit (9) and is subjected to low frequency conversion. The low-frequency converted carrier color signal and the FM luminance signal are combined in a combiner (8) and then recorded by the head H.

In this recording system 01, a pre-emphasis circuit for high frequency compensation is provided before the clamp circuit (5).

Is this pre-emphasis circuit (1) a bypass filter as shown in Figure 2? It consists of a limiter amplifier (a) and a synthesizer (goods), and the high frequency component YH of 1 to 2 MHz or more is extracted from the luminance signal band by the high t + filter (b), and this high frequency component YH is After being appropriately limited, it is combined with the luminance signal Y to emphasize the response of the high-frequency luminance signal, which deteriorates due to noise cancellation processing.

Since the frequency characteristic of the luminance signal after high-frequency emphasis is as shown by the curve t2 in FIG. 3, the overall frequency characteristic after noise cancellation is as shown by the curve t3 in FIG. 3.

As is clear from this curve diagram, the overall frequency characteristics are improved by the pre-emphasis processing.

However, in the Nori-emphasis circuit (A), it is generally difficult to provide a frequency characteristic that is opposite to the curve t in Figure 3, so the frequency characteristic inevitably becomes the one shown by the curve t5, and the 2MHz that contributes to resolution It is not possible to sufficiently improve the response in the vicinity. Therefore, even if the preence phasing circuit (1) is provided in the recording system 01,
The frequency characteristics around 2 MHz deteriorated, and the resolution could not be sufficiently improved.

Purpose of the Invention Therefore, the present invention aims to improve the resolution by preventing the frequency characteristics around 2.0 Fi[(z from deteriorating).

Summary of the Invention Therefore, in this invention, two high-noise filters with different cutoff frequencies are used, and the high-frequency components obtained from each filter are combined to suppress the drop in response especially in the above-mentioned band. It is something.

EXAMPLE Next, an example of the present invention will be explained in detail with reference to FIG. 4 and subsequent figures.

FIG. 4 shows an example of the normal emphasis circuit according to the present invention, in which a 10th pass filter Q]) selected for the first cut-off frequency 11 and a first beam filter 7° (a) are provided. The first high-frequency component Yt1 thus obtained is added to the wide-band luminance signal Y in the synthesizer (c), and the second high-frequency component Yt1 whose cutoff frequency is set to a frequency 12 higher than the frequency f is added. No.pass filter (c)
A second limiter amplifier (c) is provided, and the second high-frequency component Yt2 obtained by this is supplied to a synthesizer (c) and added. (Foundation) is a variable resistor for level adjustment.

The first cutoff frequency f is 880kHz in this example
while the second cutoff frequency f
2 is selected to be approximately 1.6 MHz. Therefore, the first high frequency component y4. The frequency characteristics of the second high-frequency component Yt2 are as shown in curve tb in Figure 5, and the frequency characteristics of the second high-frequency component Yt2 are as shown in curve tb.When the image frequency characteristics are combined, a frequency characteristic as shown in curve t0 is obtained. .

In this example, the frequency response increases by 4 to 6 dB in the 1 to 2 MHz frequency band.

Therefore, the overall frequency characteristic of the pre-emphasis circuit is curve t in Figure 6. If the frequency band of 1 to 2 MHz is sufficiently emphasized as shown in the figure, the frequency characteristic after noise cancellation becomes 1 to 2 MHz, as shown by the curve t.
It is possible to suppress a decrease in response around MHz.

First and second cutoff frequencies f1. The setting conditions for the output levels of f2 and the second high-frequency component Yt2 are determined by the frequency characteristics t of the noise canceling circuit, so the above example is just an example.

In this way, the first and second cutoff frequencies f1+7
First and second high frequency components Yt obtained by differentiating 2Th
1 + Yt2 'e, it is possible to sufficiently emphasize the frequency response in the desired band, and it is also relatively easy to obtain a frequency characteristic t that is close to the opposite characteristic to the frequency characteristic t of the noise canceling circuit. Therefore, the overall frequency characteristics of the recording/reproducing system can be improved with a relatively simple circuit configuration, and it is possible to prevent deterioration in image quality due to resolution deterioration.

As described in detail of the invention, according to this invention, it is possible to improve the deterioration of frequency characteristics caused by the noise canceling circuit provided in the reproduction system (6), thereby improving the resolution and image quality. .

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a recording system used to explain the present invention, FIG. 2 is a system diagram showing an example of a conventional pre-emphasis circuit, and FIG. 3 is a frequency characteristic diagram used to explain its operation. FIG. 4 is a system diagram showing an example of a pre-emphasis circuit according to the present invention, and FIGS. 5 and 6 are frequency characteristic diagrams for explaining its operation. α0 is the recording system, (A) is the Norien 7 assist circuit, ■n,
w are the first and second high filters, (a) and (c) are the first and second filters. It is. (7) Unexamined Japanese Patent Application Sho GO-140932 (4)

Claims (1)

[Claims] It has a first high frequency bypass filter and a second bypass filter whose cutoff frequency is higher than the cutoff frequency of the first bypass filter, and a luminance signal is supplied to these filters and the first and second high frequency filters are respectively supplied. Obtain the ingredients, these first and second
A tree emphasis circuit that adds a high-frequency component of the above to the luminance signal to compensate for the high-frequency component degraded by noise cancellation processing during playback.