JPS6214777Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a white peak clip circuit in a video amplification circuit in a color television receiver.

Conventionally, the video amplification circuit of a color television receiver generally includes a brightness adjustment circuit, a brightness limiter circuit,
It includes a white peak clip circuit, etc. To give an overview now, the block circuit diagram corresponds to the part enclosed by the broken line in FIG. 1 removed, and the removed part will be explained below.

First, the video signal detected in the previous stage is sent to video amplifier 1.
The signal is input to and amplified by the video drive circuit 2, and further voltage amplified by the video drive circuit 2, and then input to the RGB output circuit 3. On the other hand, before the video signal enters the video amplifier 1, the pedestal is clamped by the pedestal clamp circuit 4 using the clamping reference potential 5 obtained from the brightness adjuster 6 and the beam current detector 7. A limiter operation is performed.

Next, when the brightness adjustment is performed, the pedestal of the video signal changes to the adjusted level. However, since the bias 8 input to the switch circuit 9 is always fixed and constant, regardless of the fluctuation of the pedestal of the video signal input to the input terminal of the RGB output circuit 3, the potential at which the white peak is clipped is fixed. Therefore, the magnitude of the white peak to be clipped changes when the pedestal level is used as the reference, which changes the effect of the white peak on the image and deteriorates the image quality.

Furthermore, when the brightness limiter operates next time, the brightness limiter circuit is separated from the white peak clamp circuit, but the fixed bias 8 for clamping in the white peak clamp circuit is still applied to the input terminal of the RGB output circuit 3 through the switch circuit 9. Therefore, even though the pedestal of the video signal changes, the potential at which the white peak is clamped is fixed, so the size of the white peak that is clipped changes when the pedestal level is referenced, and the image This has the drawback of changing the effect of the white peak and deteriorating the image quality.

As mentioned above, the purpose of the present invention is to
When the brightness is adjusted or the brightness limiter is activated, the potential at which the white peak is clipped remains constant, even though the pedestal level of the video signal changes, so the white peak is clipped from the pedestal level. It eliminates all the drawbacks of the white peak varying in size up to the point, resulting in deterioration of image quality, and even in such cases, the white peak is always clipped at a point of constant size from the pedestal level. However, it is an object of the present invention to provide a white peak clipping circuit that always maintains the image quality in the best condition.

Describing the configuration of the present invention, the present invention performs brightness adjustment and brightness limiter by clamping the pedestal of the video signal using the DC potential obtained from the brightness adjuster and the beam current detector in the video amplifier circuit. In a color television receiver that clips the white peak of a video signal through a circuit, a variation in the clamping DC potential is detected, and this detected potential is DC amplified with an amplification equal to the amplification of the video amplifier, This white peak clip circuit is equipped with a clamp potential fluctuation detector whose output potential is used as the input potential to the clip circuit.

Hereinafter, the present invention will be explained by way of examples with reference to the drawings.

FIG. 2 shows a circuit diagram of an embodiment of the present invention. In the figure, transistor TR ₁ is for video amplification, transistor TR ₂ is for video drive, transistor TR ₃ is for pulse clamp, transistors TR ₅ , TR ₆ ,
TR ₇ is for video output (RGB output), volume resistor VR ₁ is for brightness adjustment, resistors R ₁ and R ₂ are for video amplification adjustment, and resistors R ₅ , R ₆ and R ₇ are for beam current detection. Yes, diode D ₁ is for white peak clip, diode D ₂ is for brightness limiter clamp,
These elements have been used in the past. In this invention, what is newly established is:
This is the part of the clamp potential fluctuation detector 10 surrounded by the broken line in FIG. ₂ , which is indicated by the same reference numerals as the clamp potential fluctuation detector ₁₀ in FIG. _R9 is for DC amplification adjustment.

Next, the operation shown in FIG. 2 will be explained. First, the case of brightness adjustment will be described, and then the case of brightness limiter operation will be described.

First, assume that the brightness adjustment volume resistor VR ₁ is placed at a certain position. When a video signal as shown in FIG. 2 is input to the video amplification transistor TR ₁ , the polarity of this signal is inverted at TR ₁ , and then the video drive transistor TR ₂ and the video output transistor TR ₅ are input.
~ TR ₇ , but the polarity is not reversed during this _time , so the waveform of _the video signal is has the waveform shown by the dotted line in FIG. 3a, and the pedestal level at this time is a potential of _E1 with respect to the OV of the first grid of the picture tube. At this time, if there is a white peak indicated by the dotted line in the figure, the luminance limiter lamp diode D ₂ is conducting in Figure 2, and the white peak clipping diode D ₁ is non-conducting at the white peak and conducting at other than the white peak. Therefore, the white peak is shown in Figure 2.
It is clipped at the Es potential in Figure 3a, which corresponds to the _B2 voltage, and the height of the white peak is _h1 .

Next, if we adjust the brightness adjustment volume resistor VR ₁ to increase the brightness, the video signal in Figure 3a will have the waveform shown by the solid line in the figure where the clamp level has decreased by △V ₁ and is at potential E ₂ . becomes. In this case, the white peak similarly drops by ΔV ₁ .

In the conventional circuit, diodes D ₂ and D ₁ are conductive in this case as well, so the clip level potential of the white peak is the same Es potential as the previous time.
The height of the clipped white peak is _h2 , which is smaller than the previous _h1 . Therefore, since the height of the white peak from the pedestal level becomes smaller, the white peak becomes weaker and the image quality deteriorates. However, in the present invention, as shown in FIG.
0, and the DC amplification degree by the DC amplification transistor TR ₄ in this is set equal to the DC amplification degree of the entire video amplifier by adjusting the resistors R ₈ and R ₉ , so the white peak clip potential also decreases by △V ₁ to become Ev, so the height of the white peak from the pedestal level to the clipped point is h ₁ , the same as before, and therefore the image quality deteriorates due to the change in the size of the white peak. There will be none.

Next, a case where the brightness limiter operates will be explained. The waveform of the video signal at the R, G, and B terminals in FIG. 2 when the luminance limiter is not operating is the waveform shown by the dotted line in FIG. 3b. Let the pedestal level at this time be _E1 .

Next, in Fig. 2, when the beam current of the picture tube exceeds a certain predetermined value, the potential on the anode side of the brightness limiter clamp diode _D2 drops from the potential of _B2 , so the diode _D2 is cut off. , the emitter potential of the pulse clamp transistor _TR3 also drops, and the clamp potential drops.
Therefore, the pedestal level of the video signal waveform shown in FIG. 3b increases by ΔV ₂ from the previous E ₁ to E ₃ . In addition, in FIG. 2, when the emitter potential of the pulse clamp transistor TR ₃ drops, the clamp potential fluctuation detector 10 detects this and inverts and amplifies it, and the DC amplification degree increases as described above. Since it is set to be equal to the DC amplification of the entire amplifier, the potential for white peak clamping also increases by ΔV ₂ as shown in FIG. 3b. Therefore, the height from the pedestal level of the white peak to the point where it is clipped is h ₁ and the same both before and after the brightness limiter operates, and there is no change in the image quality of the white peak, and there is no deterioration in image quality. .

As described above, when the present invention is used, the size of the white peak from the pedestal level to the clipped point is always kept constant even when the pedestal level changes during brightness adjustment or brightness limiter operation. Therefore, there is no change in the image quality of the white peak. Furthermore, due to the effect of this invention, even if the characteristics of the transistors used in the video amplification circuit and the picture tube vary, and the pedestal level fluctuates, the white peak is always clipped at a constant length. An excellent effect can be obtained in that there is no deterioration in image quality due to fluctuations in peak size.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing the operating principle of the circuit according to the present invention in relation to the entire video amplifier circuit, Fig. 2 is a circuit diagram of an embodiment of the invention, and Fig. 3 shows the operation of Fig. 2. A video signal waveform diagram at the video output end is shown for explanation. The symbols used in the drawings indicate the following. TR ₁ : Transistor for video amplification, TR ₂ : Transistor for video drive, TR ₃ : Transistor for pulse clamp, TR ₄ : Transistor for detecting clamp potential fluctuation, TR ₅ to _{TR 7} : Transistor for video output, VR ₁ ...Volume resistance for brightness adjustment, R ₁ , R ₂ ...Resistance for video amplification adjustment, R ₅ ,
R ₆ , R ₇ ... Resistor for beam current detection, D ₁ ... Diode for white peak clip, D ₂ ... Diode for brightness limiter clamp, 10 ... Clamp potential fluctuation detector.

Claims (1)

[Scope of utility model registration request] In the video amplification circuit, brightness adjustment and brightness limiter are performed by clamping the pedestal of the video signal using the DC potential obtained from the brightness adjuster and beam current detector, and the white peak of the video signal is clipped via the clipping circuit. In a color television receiver, a variation in the DC potential for clamping is detected, this detected potential is DC amplified with an amplification degree equal to the amplification degree of the video amplifier, and the output potential is used as the clip level to the clip circuit. 1. A white peak clipping circuit comprising a clamp potential fluctuation detector, wherein the clipping circuit clips a white peak at a potential with a constant potential difference from a pedestal level of a video signal.