JPH0585116B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a color cathode ray tube (hereinafter referred to as
It's called CRT. ) and relates to a brightness adjustment circuit for a video output circuit of a television receiver.

(b) Prior art The relationship between the cathode-to-grid voltage (VkG ₁ ) between the cathode (K) of the CRT and the first grid G ₁ and the optical output is as shown in Figure 4, and the optical output is Cathode cutoff voltage (Ekco) indicating rising voltage
exhibits different voltage values depending on the R, G, and B colors. Therefore, in order to improve the white balance when the screen is dark, the cut-off pressures ( Ekco). This is generally called cutoff adjustment, and it adjusts the white balance in low-luminance areas.

FIG. 2 shows a brightness adjustment circuit for a video output circuit using the cathode clamp method. 1 has an in-line electronic system (only the cathode electrodes are independent for R, G, and B, and the first and second grid electrodes are common for R, G, and B)
In a CRT, Rk, Gk, and Bk are cathode terminals, respectively, and G ₁
is the first grid and _G2 is the second grid. 2
is the brightness adjustment pressure, 3R, 3G, 3B are video output amplifiers, 4R, 4G, 4B are clamp transistors that input clamp pulses to the base, 5R, 5
G and 5B are cut-off level setting voltages.

In this brightness adjustment circuit, the video signals input to the video output amplifiers 3R, 3G, and 3B are amplified to the extent that sufficient brightness can be obtained, and then output to the cathode terminal of the CRT 1. At this time, the DC component of the video signal is blocked by capacitors 6R, 6G, and 6B, and DC reproduction is performed by clamp transistors 4R, 4G, and 4B during the black level period.
The DC potentials of the cathodes Rk, Gk, and Bk are set independently for R, G, and B by cutoff level setting voltages, and can be made to match the cutoff voltage of the CRT 1. Cutoff adjustment is performed in this manner.

In this brightness adjustment circuit, in order to increase the brightness, the potential of the _first grid G1 is changed to R, G,
This is done by changing B in common. However, R.
Since the gradients of the G and B cathode grid voltages Vk _{and G1} vs. light output characteristics are different as shown in Figure 4, the black level of the video signal is in a state that matches the cutoff level. Also 1st Grid G ₁
The uniformity of the light output is not maintained after and before the potential is changed, and the white balance is disrupted.

A brightness adjustment circuit disclosed in Japanese Unexamined Patent Publication No. 60-74792 solves this drawback. Third
The figure is a circuit configuration diagram of this brightness adjustment circuit, and the same parts as in FIG. 2 are given the same reference numerals. For simplicity, only one channel for R is shown in Figure 3, but in an actual circuit, the same channel is used for G and B.
added for use.

In the figure, r ₁ is a cut-off voltage setting resistor, and r ₂ is a gain adjustment resistor.

In this brightness adjustment circuit, the voltage of the brightness adjustment voltage 8 is made high enough to cut off the transistor 7. In this state, the cutoff voltage setting resistor _r1 changes the static bias current of the transistor 9R, the common collector amplifier of the transistor 10R lowers the output impedance, the emitter potential of the clamp transistor 4R is fixed, and the cutoff voltage is set. Next, the transistor 7 is activated, and the gain of the transistor 9R functioning as an amplifier is set independently of G and B by the gain adjustment resistor _r2 , and the slope of the optical output characteristic of R is corrected.
Gain adjustment resistor is also used to correct the slope of G and B optical output characteristics.
It is similarly corrected by r ₄ and r ₅ .

In this circuit, the common brightness adjustment voltage 8 is amplified according to the amplification degree of each of R, G, and B and superimposed on the set voltage of the cutoff level set by the cutoff voltage setting resistor _r1 etc. When the brightness adjustment voltage 8 is changed, the voltage is changed in accordance with the gradient of the R, G, and B light output characteristics, thereby preventing the white balance from being disrupted.

At this time, the collector voltage of the transistor 9R is
V ₉ c is the collector current of the transistor 9R, I ₉ c
Then, it is given by V ₉ c=V _BB −r3I9c.

Furthermore, if the currents flowing through the cut-off voltage setting resistor r ₁ and the gain adjusting resistor r ₂ are I ₁ and I ₂ , respectively, then I ₉ c≒I ₁ + I ₂ , so V ₉ c=V _BB − r ₃ ( I ₁ + I ₂ ). Then, when the brightness adjustment voltage 8 is lowered after the cutoff adjustment, the current _I2 increases and the collector current _Ic1 increases. For this reason, the collector voltage V ₉ c
decreases, the charging voltage of the capacitor C decreases, and the voltage _V1 , which is the voltage at the cathode Rk, also decreases. Therefore, the brightness of the screen becomes brighter.

However, in the case of the above conventional example, when the brightness adjustment voltage 8 is lowered and the current I ₂ is increased after the cut-off adjustment, as can be seen from _FIG . Increases by _9BE . Therefore, the emitter potential of the transistor 9R decreases by △V _9BE , and as can be seen from equation (1), the cutoff setting voltage set by the cutoff voltage setting resistor r ₁ also changes by r ₃ /r ₁ ×△V _9BE . do. Moreover, since the value of r ₁ is variable, this change cannot be predicted in advance, and the larger the value of r ₃ /r ₁ , the more the cutoff voltage will deviate from the adjustment point by adjusting the brightness adjustment voltage 8. This affects the white balance on the black level side.

(c) Problems to be Solved by the Invention The present invention has been developed in view of the above-mentioned drawbacks of the conventional example, and it prevents the deterioration of white balance due to the difference in light output characteristics of each color of R, G, and B, and also provides cut-off adjustment. It is an object of the present invention to provide a brightness adjustment circuit that prevents a set cutoff voltage from changing due to brightness adjustment and reduces deterioration of white balance on the black level side.

(d) Means for Solving the Problems The present invention provides the R (red), G
In a brightness adjustment circuit for a television receiver that sets the cut-off voltage applied to each of the (green) and B (blue) cathodes, a brightness adjustment voltage source for generating a voltage for adjusting the brightness, and a brightness adjustment voltage source for generating a voltage for adjusting the brightness are used. It consists of an amplification transistor for amplifying the brightness adjustment voltage from the adjustment voltage source and a cut-off level setting voltage transistor for supplying the cut-off voltage, and the brightness adjustment voltage is applied to the base of the amplification transistor via a variable resistor. The first terminal of the amplifying transistor is connected to ground, the cut-off level setting transistor is connected to the second terminal via a resistor, and a clamp transistor is further connected to the second terminal. This is a brightness adjustment circuit.

(E) Effect According to the above configuration, R, G, and B
The gradient of the light output characteristics of each color is corrected, and the cutoff voltage is determined by the base voltage of the cutoff voltage setting transistor, so that the cutoff voltage does not change even if the brightness adjustment voltage is changed.

(f) Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit configuration diagram of the main parts of the brightness adjustment circuit of this embodiment, and the same parts as in FIG. 3 are given the same reference numerals.
The explanation refers to the explanation of FIG. 3.

In the figure, r ₆ and r ₇ are cut-off voltage setting resistors, which are connected to the base of the cut-off voltage setting transistor 11R. The transistor 11
The emitter of R is the transistor 12R which acts as a DC amplifier which determines the clamping voltage via the resistor _r8 .
connected to the collector. The base of the transistor 12R is connected to a gain adjustment resistor _r9 that corrects the slope of the optical output characteristic. Also, R, G,
The B common brightness adjustment voltage 8 is connected to the base of the transistor 13R, and connected to the base of the transistor 12R via the emitter of the transistor 13R and the gain adjustment resistor _r9 . 13G and 13B are G and B transistors.

Next, the operation of the circuit of this embodiment will be explained. First, the collector current I ₁₂ c of the transistor 12R is changed by lowering the brightness adjustment voltage 8 and cutting off the transistor 13R, and then adjusting the resistance values of the cut-off voltage setting resistors r ₆ and r ₇ .
As a result, the base potential of the transistor 10R changes, and the emitter potential of the transistor 4R connected to the emitter of the transistor 10R, that is, the clamp voltage of the cathode Rk, is adjusted. Then, cutoff adjustment is performed by making this clamp voltage match the cutoff voltage.

Further, a brightness control voltage determined by the brightness adjustment voltage 8 is applied to the base of the transistor 12R according to the voltage division ratio of the gain adjustment resistor _r9 . The transistor 12R amplifies the brightness control voltage and superimposes it on the cutoff voltage provided by the transistor 11R. At this time, by changing the voltage division ratio of the gain adjustment resistor _r9 , the luminance change transmission rate of R to the cathode Rk is set independently of G and B. Also, G, B cards R _G ,
The luminance change transmission rate for R _B is also transistor 1, respectively.
They are independently set by gain adjustment resistors (not shown) connected to the emitters of 3G and 13B. Therefore, deterioration of the white balance of the screen due to the difference in the slope of the light output characteristics of the R, G, and B colors of the CRT is prevented.

In addition, the collector voltage V12c of the transistor 12R is V12c=V _11B −V _11BE )−r ₈ I12c (where V11B: the base voltage of the transistor 11R, V11BE: the base voltage of the transistor 11R,
I12c≒V12B−V12BE/r ₁₀ (However, V2B: Base voltage of transistor 12R V12BE: Base-emitter voltage of transistor 12R) Therefore, V12c=(V11B−V11BE) r ₃ / r ₁₀ (V12B− V12BE).

As can be understood from this formula, the collector voltage
V12c is determined by the term related to the DC amplification factor of the transistor 12R, that is, _r8 / _r10 (V12B-V12BE). Therefore, even if the brightness adjustment voltage is increased to brighten the brightness, the cutoff voltage does not deviate from the set value of the cutoff level, and there is little effect on the white balance on the black level side.

Incidentally, the present invention is also applicable to a projection television in which R, G, and B cathode ray tube electron guns are independent.

(G) Effects of the Invention According to the present invention, deterioration of white balance due to different light output characteristics of each color of R, G, and B can be prevented, and the cutoff setting voltage set by cutoff adjustment can be changed by brightness adjustment. It is possible to provide a brightness adjustment circuit that prevents this and reduces deterioration of white balance on the black level side.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a brightness adjustment circuit of the present invention,
FIGS. 2 and 3 are circuit configuration diagrams of conventional brightness adjustment circuits, respectively. FIG. 4 is a diagram showing the relationship between the cathode-grid voltage and optical output, and FIG. 5 is a diagram showing the relationship between the base-emitter voltage and collector current of the amplifying transistor. 4R...Clamp transistor, 8...Brightness adjustment voltage, 11R...Cut-off voltage setting transistor, 12R...Amplification transistor, _r8 ,
r ₁₀ ...Resistance, r ₉ ...Variable resistance, Rk...Cathode.

Claims (1)

[Claims] 1. R (red), G (green), B (blue) through a clamp transistor to which a clamp pulse is applied to the base.
A brightness adjustment circuit for a television receiver configured to set a cut-off voltage applied to each cathode includes a brightness adjustment voltage source for generating a voltage for adjusting brightness, and a brightness adjustment circuit from the brightness adjustment voltage source. It consists of an amplification transistor for amplifying voltage and a cutoff level setting voltage transistor for supplying the cutoff voltage, and the brightness adjustment voltage is applied to the base of the amplification transistor via a variable resistor. A first terminal of the amplifying transistor is connected to ground, a second terminal is connected to the cut-off level setting transistor via a resistor, and the clamp transistor is further connected. brightness adjustment circuit.