JPH0530522A - Image receiving tube driving circuit - Google Patents

Abstract

PURPOSE:To obtain an image receiving tube driving circuit capable of reducing the power consumption of respective video output circuits and attaining DC coupling. CONSTITUTION:Voltage is applied from respective floating power supplies ED1, ED2, ED3 to respective video output circuits D1, D2, D3. Respective floating power supplies ED1, ED<2>, ED3, are set up so as to be higher than ground potential by respective variable voltage circuits REG1, REG2, REG3. Thereby when video signals are directly connected to an image receiving tube, cathod cut-off adjusting voltages can be impressed by the circuits REG1 to REG3 and the load of the circuits D1 to D2 can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a picture tube, and more particularly to a drive circuit suitable for driving a high definition cathode ray tube.

[0002]

2. Description of the Related Art In a picture tube drive circuit of a color image receiver, the beam currents of three electron guns are converted into color difference signals E _R -E _Y
It is controlled by E _G -E _Y and E _B -E _Y , but an in-line type picture tube is common to 3 electron guns.
Since there are only one grid (common grid) electrode, generally, three cathode color signals (R,
G, B) is directly added to the primary color drive system.

Further, in such a primary color drive system, in order to achieve white balance of the picture tube, at least the primary color drive signal applied to each electron gun has a cutoff voltage generated between the cathodes of the picture tube. It is necessary to apply a DC voltage that absorbs the variation of.

FIG. 3 (a) shows a general conventional circuit of the primary color drive system. The color difference signals E _R -E _Y , E
_G -E _Y, and includes an output transistor Q _R, Q _G, Q _B to amplify the E _B -E _Y, the emitter follower transistor Q _Y to the luminance signal E _Y is supplied. Each output transistor Q _R, Q _G, the load resistor to the collector of Q _B R
_A power supply E is supplied via _L , and each emitter is connected in common cathode form with an emitter follower transistor Q _Y to form primary color signals R, G, B.
The output signals of the transistors Q _R , Q _G , and Q _B are directly supplied to the cathode forming the three-electron gun of the picture tube.

According to this drive method, FIG.
As shown in, the cutoff adjustment such that the cathode currents I _G , I _R , and I _B become 0 at the same cathode voltage causes a variation ΔE _{KCO in} each cathode voltage with respect to a predetermined screen voltage G ₂ . Therefore, this cutoff adjustment voltage Δ
To provide a predetermined cut voltage including E _KCO, each transistor Q _R, Q _G, the resistance value of the volume resistance R _E of Q _B is adjusted. That is, the cutoff voltage of the picture tube is supplied by utilizing the voltage drop due to the current flowing through the load resistance R _L.

[0006]

In the case of a high-resolution television receiver, the load resistance R _{L of} each output transistor is required because the signal band of the drive signal needs to be widened.
Is set to a small value (several hundred Ω), but in this case as well, in order to give a predetermined cathode cutoff voltage, it is necessary to increase the collector current flowing in each output transistor, and thus to increase the power supply voltage. In addition, there is a problem that the output transistor becomes large and power consumption increases.

Therefore, it is conceivable to replace the DC direct connection system with a capacitor coupling between the cathode electrode and the output transistor and superimpose and supply the cutoff voltage by the DC component regeneration circuit provided on the cathode electrode side. in this case,
Due to the coupling capacitor, sag is likely to occur during the V blanking period, which deteriorates the image quality. Further, since the current for charging the coupling capacitor for clamping at the pedestal level flows through the load resistance, the voltage drop in the load resistance causes a level change of the pedestal potential, which causes smear and deteriorates the image quality.

[0008]

In order to solve such a problem, the present invention amplifies a video signal in which a direct current component is reproduced, and the output thereof is direct current coupled to a cathode electrode of a common grid type picture tube. In a picture tube drive circuit provided with a video output circuit, a floating voltage for operating the video output circuit is provided, and the floating power supply itself supplies a variable voltage for supplying a cutoff adjustment voltage (ΔE _KCO ) of the picture tube. It is configured to float above the ground voltage depending on the source.

[0009]

Since the operating power supply of the video output circuit is composed of a floating voltage source, and the floating power supply itself is configured to have a predetermined voltage with respect to the ground potential by the variable power supply for cutoff adjustment, the video output When the drive signal of the circuit is DC-coupled to the cathode electrode of the picture tube, it is not necessary to set the predetermined cathode cutoff voltage by the current flowing through the load resistor. Therefore, especially in a video output circuit which supplies a drive signal to a television picture tube of high definition, the power consumption can be reduced even when the resolution is increased by using a load resistance having a low resistance value.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of a picture tube drive circuit according to the present invention. A ₁ , A ₂ and A ₃ are first amplifiers for amplifying primary color signals R, G and B respectively, and D ₁ and D ₂ , D ₃
Indicates a video output amplifier for supplying drive signals to the cathodes K ₁ , K ₂ and K ₃ electrodes of the three electron gun of the picture tube. The video output amplifiers D ₁ , D ₂ , and D ₃ are configured so that the operating voltages are individually supplied by the floating power supplies E _D1 , E _D2 , and E _D3 , respectively, and the first amplifier A ₁ ,
Primary color signals R, G, from A ₂ , A ₃ via a capacitor C
B is input respectively. It should be noted that D represents a clamp diode for direct current reproduction, for example, an input signal is clamped at a pedestal level of a video signal so that direct current reproduction is performed.

The first amplifiers A ₁ , A ₂ and A ₃ are supplied with operating voltage + V from a common low voltage source E ₁ . REG _{1 to} REG ₃ are the floating power source E
_D1 indicates a variable voltage circuit for supplying a bias voltage to each to E _D3, the variable voltage circuit REG ₁ through REG
₃ is powered by a single voltage source E ₂ .

Accordingly, the video output amplifier voltage supplied to the D _1, this when the output voltage of the variable voltage circuit REG ₁ and _{V O1 (E D1 + V O1} ) , and the operating potential difference E _D1
However, the floating voltage is biased by V _{O1 with} respect to the ground. Similarly, the video output amplifiers D ₂ and D ₃ also have variable voltage circuits REG ₂ and RE.
A bias is applied to the floating power supply by G ₃ , and V
Only _O2 and V _O3 have higher potential than the ground. Note that C
_C indicates a decoupling capacitor.

Since the picture tube drive circuit of the present invention has the circuit form as described above, the first amplifiers A ₁ , A
_The primary color signals R, E and G supplied to ₂ and A ₃ are coupled to the video output amplifier D ₁ and D ₁ via the coupling capacitor C, respectively.
It is supplied to D ₂ and D ₃ . However, clamp diode D
Since the video signal is clamped at the pedestal level of the video signal, the drive signal supplied to the cathode of the picture tube through the video output amplifiers D ₁ , D ₂ and D ₃ is the DC signal reproduced.

In the picture tube drive circuit of the present invention, the operating voltages of the video output amplifiers D ₁ , D ₂ and D ₃ are supplied from the floating power supplies E _D1 , E _D2 and E _D3 , respectively. Variable voltage circuit REG
It is biased by the output voltages V _{O1 to} V _O3 of _{1 to} REG ₃ , respectively. Therefore, in addition to the drive signal, the bias voltages V _O1 , V _O2 ,
D _O2 is superimposed.

Since the bias voltages V _O1 , V _O2 , and V _O3 output from the variable voltage circuits REG _{1 to} REG ₃ can be adjusted so as to correspond to the cathode cutoff voltage described above,
Even if the variation (ΔE _KCO ) of the cathode cutoff voltage is included, the cut voltage of each drive circuit can be adjusted. As described above, in the picture tube drive circuit of the present invention, the operating power supply of the video output circuit for supplying the drive signals of the primary colors is the floating power supply, and the floating power supply itself is used to superimpose the cutoff voltage on the drive signal. Since a variable voltage circuit that biases is provided, especially in the case of a high-resolution TV receiver,
The power consumption of the video output amplifier can be reduced. The technical means of the present invention can also be applied to a video output circuit in a monochrome high resolution television receiver.

FIG. 2 shows a more detailed circuit of the present invention. In this figure, 20R shows a video output circuit for the primary color signal R, and 20G and 20B show video output circuits for the primary color signal G and the primary color signal B. However, the detailed circuit configuration is the same as that of the video output circuit 10R, and therefore the illustration is omitted.

Each video output circuit 20R (20G, 20
B), the alternating power supplied from the step-up coil L _2, L _3, L _4, which are respectively coupled to the switching power supply 10A, rectifies the alternating output diode D _1, D ₂ and a capacitor C _1, C ₂ By doing so, the operating power source that is being floated is obtained. The video signal R (G, B) input from the terminal T ₁ is 30R (30G, 30B)
Is supplied to the first amplifier section indicated by. The first amplifier section 30R (30G, 30B) is provided with a drive adjustment volume VR ₁ for varying the input signal level, a transistor Q ₁ , a collector resistance R ₁ and a coupling capacitor C _4, and a bias resistance r ₁ , r ₂ and capacitor c ₃ are provided. Then, each of the first amplifier sections is operated by the voltage + V ₁ supplied from the power supply section 50, and the output of the first amplifier section is reproduced by the clamp diode D ₃ and the time constant resistance r ₃ and then the video output amplifier section. Are supplied to the transistors Q ₂ , Q ₃ , and Q ₄ which form

Transistor Q connected in cascade
Reference numeral ₄ is a grounded base type, and a load resistance R ₃ of several 100 Ω is connected to its collector. The video signal output from one end of the load resistor R ₃ is DC-coupled to the cathode K _{R of a} picture tube (not shown) via the peaking coil L and the resistor r ₅ . Incidentally, D ₄ and D ₅ are protection diodes, and r ₆ and S _P are spark protection circuits.

40R surrounded by a two-dot chain line (40G, 40
B) shows a variable voltage circuit that changes the voltage + E ₂ supplied from the power supply unit 50 to bias the floating voltage source. This variable voltage circuit 40R (40G,
40B) comprises a transistor Q ₅ and a variable resistor VR ₂ for outputting a background voltage V _O which lifts the floating voltage source from ground. The diodes D ₆ and D ₇ compensate the temperature characteristic of the transistor Q ₅ .

The background voltage V _O is the three primary color signals R,
A DC offset is set in the video output signals of the video output circuits 20R, 20G, and 20B so that each electron beam of the picture tube to which G and B are supplied is cut off at the black level of the video signal. In the embodiment of the present invention, the floating voltage source itself of each video output circuit is biased. This bias amount is performed by adjusting the variable resistor VR ₂ , and the adjustment voltage is the terminal voltage of the capacitor C ₈ .

Therefore, the cut-off adjustment DC bias voltage for adjusting the white balance of the picture tube does not need to be obtained by the current flowing through the load resistor R ₃ .
Even when the load resistance R ₃ is reduced to form a high resolution video circuit, the power consumption can be reduced and the DC coupled drive can be realized. Although the above embodiment has described the color video output circuit, the drive system of the present invention can be applied to a monochrome video output circuit.

[0022]

As described above, in the picture tube drive circuit of the present invention, the operating power source of the video output amplifier is constituted by the floating power source, and the entire floating power source is set at a predetermined voltage value from the ground potential by the variable voltage circuit. Since it is biased so as to be lifted, the cutoff adjustment for achieving white balance is easily performed when the drive signal of the video output amplifier is DC-connected to the cathode of the picture tube.

Further, since the cathode bias including the cutoff adjustment voltage (ΔE _KCO ) is superposed from the external circuit,
Particularly, in the case of a high definition TV receiver, there is an advantage that power loss due to collector resistance is reduced and a low power transistor can be used.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic principle of a picture tube drive circuit of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of a picture tube drive circuit of the present invention.

FIG. 3 is an explanatory diagram showing a conventional technique of a primary color drive system.

[Explanation of symbols]

10 step-up transformer 20R, 20G, 20B video output circuit 30R, 30G, 30B First amplifier section 40R, 40G, 40B variable voltage circuit

[Procedure amendment]

[Submission date] September 30, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art A picture tube drive circuit in a color picture receiver has three primary color signals (R, G, B) for each cathode of the picture tube.
Is the primary color drive system that adds directly.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

[0004] FIG. 3 (a), shows a typical prior art circuit of primary drive system includes an output transistor Q _R for amplifying the primary color signals RGB, Q _G, the Q _B. Each output transistor Q _R, Q _G, the collector of Q _B power E is supplied through the load resistor R _L, V of the emitters is cut-off voltage adjustment to absorb a variation in the cut-off voltage It is connected to the bias voltage E _B through _R. Each transistor Q _R, Q _G, the output signal of the Q _B are supplied direct to the cathode to form the three electron guns of direct picture tube, RGB by adjusting the V _R
The cathode potential of can be changed, the variation of the cutoff voltage can be absorbed, and the white balance can be adjusted.

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

Claims (2)

[Claims] 1. A picture tube drive circuit comprising a video output circuit for amplifying a reproduced DC video signal, the output of which is DC-coupled to the cathode electrode of a common grid picture tube, wherein the video output A floating power supply for operating the circuit is provided, and the floating power supply itself is configured to float above the ground voltage by a variable voltage source that supplies a cutoff adjustment voltage (ΔE _KCO ) of the picture tube. Picture tube drive circuit. 2. A DC signal reproduced from each of the reproduced three primary color video signals is amplified, and its output is DC-coupled to each cathode electrode of a common grid type color picture tube.
In a picture tube drive circuit having a plurality of video output circuits, three independent floating power supplies for operating each of the video output circuits are provided, and each floating power supply itself adjusts each cathode cutoff of the picture tube. A picture tube drive circuit, characterized in that it is constructed so as to float above the ground voltage by three variable voltage sources that supply a voltage (ΔE _KCO ).