JPS5871769A - Control circuit of reference level - Google Patents

Abstract

PURPOSE:To perform the control of the reference level in the station at a high speed and a simple and accurate way without using any measuring instrument, by projecting pictures simultaneously on the same screen and on the basis of the reference level. CONSTITUTION:The video-amplified TV signal is supplied to a terminal 1 and then fed to a pedestal clamping circuit 2 via a transistor (TR) Q1. For the circuit 2, a TR Q2 is turned on by the clamp pulse given from a terminal 3 and the pedestal level is clamped to the level set by a volume 4. The clamped TV signal is supplied to a video output circuit 6 via the TR Q2, and the output of the circuit 6 is applied to an anode of a CRT to reproduce a prescribed video. A video switching circuit 7 is switched alternately by the switching pulse PAC, and a black level picture 11A corresponding to a period T1 of the test signal ST is projected at the center on a screen during a period T1. At the samd time, a picture 11B which is based on the reference signal SB of the set side is projected on other screens. Therefore the volume 4 is controlled so as to obtain an equal level of brightness between the pictures 11A and 11B.

Description

[Detailed description of the invention] When receiving and playing television signals.

If the reference level (black level, etc.) of this television signal does not exactly match the reference level (cutoff level of cathode tube, etc.) on the television receiver side, the television Ii of image transmission i! j image cannot be reproduced correctly on the receiver side. When using the black level as the reference level of a television signal (hereinafter referred to as the station reference level), in the case of the NTSC system, it is 7.5IRE±2.5IRE, so depending on the broadcasting station, it is not always 7.5IRE±2.5IRE. It is not always the case that MIRE is used as the station reference level.

Therefore, especially in monitor television receivers used at various broadcasting stations, the station side reference level is set to the reference level inside the television receiver, that is, the cutoff level of the cathode thin tube (hereinafter referred to as the set side reference level). There is a need to match.

Conventionally, this adjustment method uses a measuring device to adjust the station reference level, but this adjustment method requires a measuring device for adjustment, and therefore cannot be easily performed. Since the standard level on the station side is adjusted based on the measured waveform, measured value, etc., accurate level adjustment is impossible, and therefore the adjustment accuracy is poor.
One drawback is that it takes time for adjustment to improve accuracy.

Therefore, in this invention, 1i1 based on these reference levels
By displaying seven images simultaneously on the same screen and adjusting the brightness of each image to match, the station reference level can be adjusted accurately, easily, and quickly without using the measuring equipment described above. I changed it to 5.

Next, an example of the present invention will be described with reference to FIG. 1 and subsequent figures. In this example, the cutoff level of the cathode ray tube is used as the set-side reference level, and the standard system for television signals is the NT&C system.

In the figure, a video amplified television signal is supplied to terminal (1), and this is transmitted to the buffer transistor Q.
The pedestal clamp circuit (2) K is supplied via l. The clamp circuit (2) has a field effect transistor Q2 for switching, and the clamp pulse supplied to the terminal (3) turns on this transistor Q2, clamping the pedestal level to the level set by the volume control (4). ~ will be done.

The clamped television signal is supplied to the video output circuit (6) via a buffer transistor Q2.

The video output is supplied to the anode or cathode (anode in the embodiment) of a cathode ray tube (not shown) to reproduce a predetermined video.

In this example, a video switching circuit (7) is connected between the buffer transistor Q3 and the video output circuit (6), and video switching is performed when adjusting the station reference level. This video switching circuit (7) is configured as a switching circuit as shown in the figure, the terminal (a) is supplied with a pedestal clamped television signal, and the terminal (b) k is the reference level on the set side, so the cathode ray tube is connected to the terminal (b). A signal (set side reference signal) SB corresponding to the cutoff level is supplied.

That is, when this set-side reference signal sB having a predetermined DC level supplied to terminal ←)k is supplied to the cathode ray tube via the video output circuit (6), the cathode ray tube is in a cut-off state. A certain signal is used as a signal corresponding to the set-side reference level. In the example shown, the 0 level signal sB' exactly corresponds to the cutoff level of the cathode ray tube, but depending on the circuit design, a DC level signal different from the above may correspond to the cutoff level. be.

Switching of the video switching circuit (7) is controlled by the output of the switching circuit (8). This switching circuit (8)
The output rDc of the terminal (c) is used when the video switching circuit (7) is switched to the terminal (a) side for normal monitoring operation except when adjusting the reference level. When adjusting the reference level, the switching pulse PAC supplied to the terminal (e) is used. (9)
Is this the switching pulse PAC forming circuit? Well, second
A pulse with an H period as shown in Figure B is used, and the period T1
During this period, the terminal is switched to the terminal (A) side.

Note that the switching pulse PAC is the horizontal synchronization pulse pH
The pulse width TI of the switching pulse PAC and its phase can be varied, so it can be configured as 5.

When adjusting the station reference level, the switching circuit (8)
At the same time, instead of the monitor television signal, terminal (1) receives a black level of 7.5 IRE (as shown in Figure 2). A test signal ST of only the black level selected as the black level value is supplied. Therefore, the relationship between the switching pulse PAC and the test signal ST is the second
If it is like the picture.

During the level adjustment period, a TV screen as shown in Figure 3 will be displayed.

That is, the video switching circuit (7) receives the switching pulse P
It is switched alternately by AC, and during the TI period, a black level 1Iiii image (11A) corresponding to the period Tt (Fig. 2) of the test signal 8T is displayed in the center of the screen.
Other screens display images based on signals 8B and K (11B
) is displayed. Therefore, after adjusting the brightness level to brighten the screen, adjust the volume (4) provided in the pedestal clamp circuit (2).

Since the value of the pedestal level of the test signal 8T is changed, the brightness of the image (11A) can be adjusted by this polyneme (4).

Therefore, the brightness of the image (iIA) matches the brightness of the first image (IIB), and therefore the border line on the screen.

Adjust the volume (4) so that tb disappears. When the brightnesses match, it means that the black level of the test signal ST is aligned with the cutoff level of the cathode ray tube, so by adjusting the brightness in this way, you can ensure that the reference level on the station side matches the reference level on the set side. be able to. After level adjustment, switch the switching circuit (8) to the terminal (c) side.

In addition, the black level is □ in PAL television signal.
xRi, that is, the same as the pedestal level, so in this case, there is no need to use the test signal ST as shown in Figure 2 AK when adjusting the level, and a television signal with normal video information can be used. . however,
The phase and pulse width of the switching pulse PAC are chosen such that the period Tl is exactly within the horizontal blanking period.

When adjusting the level using the PAL system, an image as shown in FIG. 4 is displayed. Namely.

1lii image (IIA) regarding black level within period TI
In addition to %, an image *aa which is further black 11 than the black level due to the horizontal synchronizing pulse PH is displayed. The level adjustment is the same as above, by comparing the brightness of (11A) and (11B). Based image (IIA) and
The reference level is adjusted by displaying an image* (IIB) based on the set side reference signal sB corresponding to the set side reference level on the same screen at the same time and adjusting the brightness so that they match. Therefore, no matter what value the station side reference level is, it can be adjusted to match the set side reference level, and has the following features compared to the conventional example.

First, according to the present invention, no measuring device is required.

Therefore, adjustment work can be easily performed. Since the level adjustment is based on the brightness k of the screen, it is more accurate than when using a measuring device. That is, the image ("IA)t(11
Since the brightnesses are both fixed and the brightness of the image (IIB) and the adjacent image (IIA) are changed, it is possible to easily and accurately determine the point where the brightnesses match.

This is because when a measuring device is used, the measurement accuracy varies due to internal errors of the measuring device, and even a slight difference in waveform measurement will appear as a difference in brightness.

Therefore, according to the present invention, it is possible to accurately, simply and quickly adjust the station reference level.

In addition, in the above, the cutoff level of the cathode ray tube was used as the reference level, but the white level (for example f$QIRE)
may be used as the reference level, in which case the test signal S
The signal indicated by the broken line in FIG. 2A may be used as T (K for both NTSC and PAL systems).

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of the reference level 111 & circuit according to the present invention, FIG. 2 is a waveform diagram for explaining its operation, and FIGS. 3 and 4 are diagrams for explaining the video image, respectively. . (2) is the pedestal level clamp circuit, (6) it
Video output circuit, (7) is the video switching circuit, (81) is the switching circuit, and (4) is the volume for adjusting the pedestal level. IS, - Satsuma

Claims (1)

[Claims] A part of the screen is based on the television signal and corresponds to the bell! The other part of the screen displays an image based on a signal corresponding to the reference level of the cathode ray tube of the television receiver, and the brightness of this image is adjusted to the reference level of the television signal. 5. A reference level adjustment circuit for adjusting the reference level of the television signal so that the brightness of the image based on the signal corresponding to the television signal matches the brightness of the image.