JPS5964990A - Color television receiver - Google Patents

Abstract

PURPOSE:To obtain color pictures of high quality, by providing a control circuit which controls the bias of a video output transistor in response to a DC level and then controls the DC transmission quantity of a picture signal. CONSTITUTION:A video signal underwent video wave detection is supplied to an input terminal 11, and a video signal including a pedestal level is delivered from a video signal processing circuit 12. The DC component of the output of the circuit 12 is cut via a capacitor 13, and the output of the circuit 12 is fed to a pedestal level detector 14. The circuit 14 detects the pedestal level of the fed video signal and delivers the DC voltage corresponding to the pedestal level. Then the DC output of the circuit 14 is supplied to a black level control circuit 15, and this DC potential controls the black level of a picture signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a color television receiver (Kl), particularly a color television receiver capable of inputting three primary color signals from an external device such as a computer. The present invention relates to a color television receiver configured so that the amount of DC transmission of image signals can be arbitrarily selected.

[Technical background of the invention and its problems]

In recent years, color television reception has become increasingly popular. The tR has been systemized using VTRs and video disc playback devices as peripheral equipment.

For this reason, color television reception fS! While the machine is equipped with an external input terminal, it is also equipped with an internal switching circuit so that a desired image can be easily selected from a plurality of signal sources.

Such color television equipment is capable of switching in the standard video signal frequency band, and
In the TSC system, images produced by a composite video signal from the above-mentioned VTR, video disk reproduction device fIt, etc. are reproduced as well as conventional broadcast signals.

However, since broadcasting will start in the near future, the clock pulse that will be the basis of the x-shaped display will be at least 7.
Approximately MH2 is required.

On the other hand, the frequency bandwidth of the video signal of a color television receiver is determined to be approximately 4 MH2, and the Q signal of the I and Q color signals according to the NTSC system is 500 KHz, so the teletext receiver described above When a conventional color television receiver reproduces video signals from computers or personal computers, it is impossible to reproduce images with sufficient resolution, and the deterioration of color signals is particularly severe. .

For this reason, in order to reproduce the video signals of teletext broadcasting, personal computers, etc. mentioned above well, the video signals are converted into three primary color signals of R (red), G (green), and B (evening). Must be input into a color television receiver.

FIG. 1 is a block diagram of a color television receiver capable of inputting external three primary color signals.

In the figure, a color television signal S1 is received by an antenna 1, inputted to a tuner 2, converted into a video intermediate frequency signal S2, and then detected through a video detection circuit 3. is input to the color signal processing circuit 4 and video signal processing circuit 5 to produce color difference signals R-Y, G-Y.
.

B-Y and video signal Y are demodulated and these signals are passed through the matrix circuit 6 to produce three primary color signals R and G.

I'm trying to get Bi. The #R, G%B signals output from the matrix circuit 6 are input to the CRT drive circuit (output amplification circuit) 8 via the TV/DATA switching circuit 7, where they are amplified and then applied to the CRT (picture tube) 9. .

In FIG. 1, the TV/DATA switching circuit 7 selects Iζ, G on the television receiver side obtained by the matrix circuit 6.
, B signal and R, G, B signals inputted from an external device 10 such as a computer, the CRT drive circuit 8
This is a switching circuit for inputting to the black level, and also has a function to clamp the black level. Due to the presence of such a switching circuit, some of the most important processing functions of the video signal processing circuit 5 and color signal processing circuit 4 are not performed. The most important process is the amount of DC transmission of video signals.

As is well known, the dynamic range of brightness of a color television signal is very narrow compared to the brightness range that exists in nature. Therefore, in conventional color television receivers, the bias voltage between the cathode and grid of the CRT is varied in order to obtain a good reproduced image. The amount of DC transmission determines the brightness in this image reproduction.

Conventionally, in order to make it possible to input external three primary color signals as shown in Fig. 1, it was necessary to stabilize the black level of the TV/D.
Pedestal clamping is performed in the ATA switching circuit 7, so that even if the brightness of the image changes, the black level is kept constant so that an average brightness is always obtained. In this case, the amount of DC transmission cannot take a value other than 100 inches. When pedestal clamping is performed in this way and the amount of DC transmission is 100 cm, for example, if the signal content is an overall dark image such as a night view (in other words, UV4i
For images with average video level and low PL, most of the information is C.
There was a problem in that the potential was close to the cut-off potential of RT, resulting in an extremely difficult to view image.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to provide a color television receiver in which the amount of direct current transmission of an image signal input to a picture tube can be arbitrarily selected.

[Summary of the invention]

The color television receiver of the present invention includes a video signal processing means, a transmission means for transmitting only the alternating current component of the video signal output from the video signal processing means, and a switching operation synchronized with the pedestal period of the video signal. Go 111
A switching means for transmitting the output of the transmission means described in j only during the pedestal period, a DC level generation means for outputting a DC level according to the output of the switching means, and a video output transistor, and a picture tube drive output is obtained at the output end of the switching means. The apparatus comprises a video output means and a control means for controlling the bias of the sub-image output transistor according to the DC level, and the control means sets the black level by controlling the transmission amount of the DC component of the image signal. It is.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 2 is a blog diagram showing the main parts of a color television receiver according to the present invention.

In FIG. 2, a detected video signal is input to an input terminal 11, and a video signal processing circuit 12 outputs a video signal including a pedestal level. This circuit 12 corresponds to the video signal processing circuit 5 shown in FIG. circuit 1
2 is passed through a capacitor 1311- to cut off its DC component, and then input to the pedestal level detection circuit 14. The pedestal level detection circuit 14 detects the pedestal level of the input video signal and outputs a DC voltage corresponding to the pedestal level. The DC (output) of the circuit 14 is input to a black level control circuit 15, and the black level control or system determination of the image signal is performed based on the DC potential.
'It is provided at a position corresponding to the ATA switching circuit 7.

FIG. 8 is a circuit diagram showing the main parts of the color television receiver according to the present invention, and FIG. 4 is a waveform diagram showing the input end pre-charge and the signal input to C.

In Fig. 8, the terminal to which the video signal is input is the detection circuit 14, the DC power supply element B is connected to the resistor R3, the base of the transistor Q is connected to the terminal to which the clamp pulse is input via the resistor R1. The emitter d of the transistor Q is connected to the base of the transistor Q, which has an emitter-follower configuration, and one end of its emitter resistor R6 is grounded, its collector is connected to the DC power supply element B, and the emitter d of the transistor Q is connected to the base of the transistor Q, which has an emitter follower configuration. There is a capacitor C on both ends of R1! Le5lrll (++
1 circuit lb connects the base of a transistor Q with an emitter-follower configuration to the output terminal e, and
The collector of s is grounded, the emitter output terminal f is connected to the DC power supply element B via the emitter resistor Rsf, and the output terminal f is connected to the CRT drive circuit 16.

The C1tT drive circuit 16 also connects a capacitor Csf to a terminal g to which any one of the G%B three primary color signals is input.
The base of the output transistor Q4 is connected through the resistor R?, and its emitter is connected to the resistor R? The emitter output terminal f of the transistor Q3 is connected through the resistor R0, and the collector thereof is connected to the DC power supply element B2'F-1 through the resistor R0, while being connected to the cathode of the CRT 17.

Transistor Q constituting the black level control circuit 15
From the emitter output terminal f of , jji, i Lk point and i are also connected to a circuit similar to the circuit consisting of transistor Q4, resistors R, , R, and capacitor C5. It is configured to output to 3.

In such a configuration, it is assumed that the signal shown in FIG. 4a is input to input point aK. The signal shown in FIG. 4a is the first speed signal S included in the pedestal level P' and has synchronization (g signal N''f-).

If < if determined by the value of the current voltage source 1B,
Achieved +L 'U position (, 4th wave was obtained. Point OK
A fourth pulse (shown in IC) is applied. This pulse is a timed clamp pulse S, which separates the synchronization signal N from the back porch portion of the blanking period of the video signal. It can be created by shaping the trailing edge pulse obtained by differentiating the delayed synchronization signal.When the crank pulse S2 is input to the input terminal C, the transistor is activated only when this pulse is input. Q, conducts and saturates, transmitting the potential at point d to the emitter side point d of transistor Q. The circuit consisting of transistor Q! and resistor R4 is an emitter-follower circuit, and capacitor C2 is connected to its emitter. Since the time constants R and C of the RC circuit formed by the resistor R4 and the capacitor C1 are sufficiently large values, the potential at the output point θ of the transistor Q2 is equal to the input point d.

The DC potential becomes approximately equal to level flt. Further, the circuit consisting of the transistor Qs, 4'f anti-t<, is also an emitter follower circuit, and this circuit supplies the potential obtained at the output point f to the emitter of the output transistor Q4. The potential at the output point f is V due to the bias voltage supplied to the emitter of the transistor Q4, and the brightness of the screen, that is, the black level fa can be controlled by this level 1i.

FIG. 5 is a graph showing the change in the pedestal potential Vv at a point with respect to the average projection level (APL) K.

In Fig. 5, if the horizontal axis is APL (0 to 100%) and the vertical axis is the pedestal potential V←, then API, 0
%, the potential at point f shows a similar change with respect to the value of APL, as can be seen from the circuit operation described above.

The total AC amplitude of the signals applied to points a and g is 1 and v, respectively.
Since it is supplied via the V and H contactors tJCl, the DC component is output as an APLI signal. Also, since the signal (2) is supplied via the capacitor Csk, that signal is output. Therefore, point a1g! F-v1, v! is added, the collector VC of transistor Q becomes 1,000° DC,
The DC transmission quantity is expressed by vl and vl. therefore,
By changing the magnitude of the AC amplitude V of the video signal input to point a, the DC transmission scale can be arbitrarily selected.

[Effects of the Invention] As described above, according to the present invention, in a color television receiver fR, after cutting the DC component of a video signal, the pedestal level f'jUk3 L of this video signal is
, outputs full DC heavy pressure equivalent to the pedestal level,
A circuit that controls the amount of DC transmission of the f-area tube drive signal using this DC' low voltage? With this configuration, it is possible to arbitrarily select the amount of DC transmission to set all black levels, and this can be realized with a very simple circuit configuration.

Figure 1 is a block diagram of a color television receiver capable of inputting external three primary color signals from an external device 6 such as a computer; Figure 2 is from this book] FIG. 8 is a block diagram showing the main parts of the color television receiver according to the present invention. FIG. 4 is a circuit diagram showing the main parts of the color television receiver according to the present invention. The waveform diagram shown in FIG.
l) It is a graph showing the change in the pedestal height Vl of the dot with respect to LK.

12...Video signal processing circuit 13...Capacitor 14...Pedestal level 44 Output ILjJ %1
5... Black level control side 1 circuit 16... CRT drive circuit 17... CRT C, -vC3... Capacitor R1~1,... Resistor Q! ~・04...Transistor +B, ,+B2...DC box; Pressure source K, ~3
...Cathode Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] A video signal processing means, a transmission means for transmitting only the alternating current component of the video signal outputted from the video signal processing means, and a switching operation synchronized with the pedestal period of the video signal. a DC level generating means that outputs a DC level according to the output of the switching means;
A color television comprising: a video output means that includes a video output transistor and obtains a picture tube drive output at its output terminal; and a control means that controls the bias of the video output transistor according to the DC level. receiver.