JPS641999B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to means for adjusting the cutoff voltage of each electron gun in an integrated electron gun color cathode ray tube drive circuit.

Figure 1 shows the characteristics between the cathode/first grid tube voltage V _KG and the light output of a color cathode ray tube (hereinafter abbreviated as CPT). The order of red (R), blue (B), and green (G) is not necessarily as shown in Figure 1, but the order of R, G,
The V _KG at which the optical output of B rises differs as shown in FIG. The voltage V _KG at which the optical output rises as shown in Figure 1, that is, V _G , V _B , _VR etc., is generally called the cut-off voltage, and when the driving voltage of each color changes from zero, the electron gun simultaneously outputs optical output. It is necessary to issue This is called cutoff voltage adjustment, and if this adjustment is incomplete, white reproducibility in dark areas of the screen will deteriorate.

The conventional cut-off voltage adjusting means will be explained below using a specific circuit.

Figure 2 is used in current color televisions.
This is an example of a CPT drive circuit. In Figure 2,
1 is CPT, 2R, 2G, 2B is load resistance, 3R,
3G, 3B are drive transistors, 4R, 4G, 4
B is cut-off voltage adjustment resistor, 5R, 5G, 5B
is a drive adjustment resistor, 6R, 6G, and 6B are color difference signals, and 7 is a luminance signal.

Generally speaking, in recent inline CPT, R, G,
The first grid of each electron gun B is commonly set to ground potential. Therefore, the cut-off voltage adjustment described above is performed by independently changing the R, G, and B cathode terminal voltages. A detailed explanation will be given below using FIG. 2.

The outputs of the color difference signal sources 6R, 6G, and 6B are set to zero,
Drive adjustment resistors 5R, 5G, and 5B are opened. At this time, drive transistors 3R, 3
Since a constant voltage E is applied to the bases of transistors G and 3B, the collector currents of drive transistors 3R, 3G and 3B are varied by changing the values of cut-off adjustment resistors 4R, 4G and 4B, respectively. As a result, the amount of voltage drop across the load resistors 2R, 2G, and 2B changes, so each cathode voltage also changes. This can be expressed as a formula as follows.

V _KG = V _CC −I _C R _L …(1) where I _C : Drive transistors 3R, 3G, 3B
Collector current R _L : Resistance values of load resistors 2R, 2G, and 2B Also, I _C in equation (1) can be expressed by the following equation.

I _C ≒ I _E = E−V _BE /R _E …(2) Here, V _BE : Drive transistors 3R, 3B, 3
G base-emitter voltage R _E :Cut-off adjustment resistor 4R, 4G,
Resistance value of 4B I _E : Drive transistor 3R, 3G, 3B
Therefore, from equations (1) and (2), we obtain V _KG = V _CC −R _L /R _E (E−V _BE )…(3). The resistors 4R, 4G, and 4B are adjusted so that V _KG expressed by equation (3) becomes the cut-off voltages V _R , V _G , and V _B of each electron gun in FIG. 1, respectively. By setting the cathode potential to the cut-off voltage of each electron gun in CPT1, white balance in dark areas of the screen can be maintained.

Adjustment of the white balance in bright areas of the screen is performed by adjusting the resistance values of the drive adjustment resistors 5R, 5G, and 5B to adjust the amplification degrees of the drive transistors 3R, 3G, and 3B. Here, color difference signals (R-Y), (G-Y), (B-Y) and luminance signal Y
are calculated by drive transistors 3R, 3G, and 3B, and respective primary color signals R, G, and B are obtained,
The cathode of CPT1 is driven. As shown in FIG. 1, the collector voltages of drive transistors 3R, 3G, and 3B vary between cut-off potential and zero potential depending on the input signal level. For this reason,
There is a large variation in the cutoff voltage of CPT1,
If the power supply voltage V _CC is low, drive transistor 3
The possible amplitude ranges of R, 3G, and 3B are extremely narrow, and high output cannot be obtained. On the other hand, if the power supply voltage V _CC is increased in order to sufficiently absorb variations in the cut-off voltage and expand the operating range of the drive transistors 3R, 3G, 3B, the load resistances 2R, 2G,
2B, drive transistors 3R, 3G, 3B, etc., increases, and this is not economical. Also power supply voltage
By increasing V _CC and increasing the load resistances 2R, 2G, 2B, the drive transistors 3R, 3
If the operating current of G, 3B is reduced and the operating range of output transistors 3R, 3G, 3B is expanded without increasing loss, the input capacitance of the cathode, the output capacitance of drive transistors 3R, 3G, 3B, other wiring, etc. Stray capacitance and load resistance of 2R, 2G, 2B
The cutoff frequency of the drive circuit system, which is determined by , decreases, making it impossible to obtain a high-resolution screen.

A specific example of a CPT drive circuit that improves the above-mentioned drawbacks is shown in FIG. In Figure 3, 8R, 8G,
8B are input terminals for primary color signals R, G, and B, respectively;
9R, 9G, 9B are amplifiers that amplify the primary color signals R, G, B; 11 is a capacitor for DC cutoff; 10
R, 10G, and 10B are DC regenerators. Amplifiers 9R, 9G, 9B each include an amplification transistor and its load resistance, and DC regenerators 10R, 10
G and 10B are transistors 13 that are turned on by the clamp pulse 12 generated during the black level period and turned off outside of the clamp pulse period, and a variable resistor 14 for adjusting the clamp voltage that divides the voltage between the DC voltages V _B1 and V _B2 . and a diode 15 that protects the transistor 13 from reverse breakdown voltage.

Regarding the R primary color signal, the DC component of the R primary color signal amplified by the amplifier 9R is removed by the capacitor 11, and the DC component is regenerated by the DC regenerator 10R and supplied to the cathode of the CPT 1. Since the DC component voltage of the primary color signal supplied to the cathode can be adjusted by adjusting the variable resistor 14, variations in the cutoff voltage of the electron gun are absorbed by this adjustment. That is, since variations in the cut-off voltage of the electron gun are adjusted by adjusting the DC regenerators 10R, 10G, and 10B, there is no need to absorb the variations in the amplifiers 9R, 9G, and 9B. There is no need to make the power supply voltage or load resistance value of 9B larger than necessary. Therefore,
The drive circuit shown in FIG. 3 almost eliminates the drawbacks of the drive circuit shown in FIG. A clamp pulse generation circuit is also required. That is, in the drive circuit of FIG. 2, it is difficult to widen the band, and in the circuit of FIG. 3, the circuit becomes complicated and the number of transistors used increases, resulting in poor economic efficiency and reliability. For example, if an abnormal discharge accident occurs in a CPT, the damage will be significant because of the presence of clamp transistors.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a wideband CPT drive circuit that can easily adjust the CPT cutoff.

The present invention provides flyback pulses for R, G, B between the CPT drive circuit output terminal and the CPT cathode terminal.
An independently rectified DC power supply is inserted, and a DC voltage that includes variations in the cutoff voltage is superimposed on the CPT drive voltage, thereby correcting variations in the cutoff voltage independently of the drive circuit.

The principle of the present invention is shown in FIG. The same parts in FIG. 4 as in FIG. 3 are given the same reference numerals. In FIG. 4, 16R, 16G, and 16B indicate output terminals of the CPT drive circuit 9. 17R, 17G, and 17B indicate variable constant voltage power supplies. The drive circuit 9 may be any amplifier that has an output voltage necessary to obtain sufficient optical output and a frequency band sufficient to obtain the required resolution. In addition, the power supply voltage supplied to the drive circuit 9 only needs to have a value sufficient to obtain the maximum output.
Since there is no need to include variations in the cut-off voltage of CPT1, the broadband characteristics shown in the conventional circuit of FIG. 3 can be maintained as is. The polarities of the variable constant voltage power supplies 17R, 17G, and 17B in FIG. 4 can also be reversed.

Next, the operation of the circuit shown in FIG. 4 will be explained. To simplify the explanation, only the R signal will be described. The R primary color signal input from the input terminal 8R is amplified by the drive amplifier 9R and output from the output terminal 16R. Here, a DC level shift occurs through the variable constant voltage source 17R, and is transmitted to the cathode terminal of CPT1. The same applies to the G and B primary color signals. The voltage values of 17R, 17G, 17B are R,
By changing G and B independently, variations in cutoff voltage can be absorbed. Further, the cutoff voltage of each electron gun can be set by setting the voltage values of the variable constant voltage power supplies 17R, 17G, and 17B at a point where the black level voltage of the CPT drive voltage is equal to the cutoff voltage.

FIG. 5 shows an embodiment of the present invention, which embodies the principle diagram of FIG. 4. The same parts as in FIG. 4 are given the same reference numerals. Further, 18 is a bypass capacitor, 19 is a smoothing capacitor, 20 is a rectifier diode, 21 is a transformer, and 22 is a flyback pulse (or a general commercial power source).

Next, the operation of the circuit shown in FIG. 5 will be explained. The secondary side of the transformer 21 is wound independently in R, G, and B, and a rectifier diode 20 is connected to each winding.
and a smoothing capacitor 19 to generate DC voltages independently for R, G, and B. The generated DC voltage is independently divided by variable resistors 4R, 4G, and 4B, and is used to absorb variations in cut-off voltage. That is, it is sufficient that the terminal voltage of the smoothing capacitor 20 is higher than the maximum value of the cut-off voltage. The circuit can be realized without the smoothing capacitor 19. The bypass capacitor 18 may be selected to have a value sufficiently lower than the impedance of the variable resistors 4R, 4G, and 4B for the video signal. Further, the currents flowing through the variable resistors 4R, 4G, and 4B are set to such an extent that the terminal voltage of the capacitor 18 does not change due to the cathode current of CPT.

To explain the operation of the R primary color signal, the R primary color video signal input from the input terminal 8R is sent to the drive circuit 9.
The voltage is amplified by the CPT, becomes a voltage of a magnitude necessary to obtain sufficient optical output from the CPT, and is output to the output terminal 16R. This driving voltage is the bypass capacitor 1
8 and is transmitted to the cathode,
At this time, the DC voltage divided by the variable resistor 4R is superimposed. In other words, a DC level shift is performed, and if the black level of the drive voltage is adjusted using the variable resistor 4R in Figure 4 so that it becomes the cutoff voltage of CPT, that is, V _R in Figure 1, the cutoff adjustment of CPT can be achieved. I can do it.

The transformer 21 in FIG. 5 can also be constructed independently for R, G, and B. The power source applied to the primary side of the transformer 21 can be either a flyback pulse or an alternating current voltage at a general commercial frequency.

Next, FIG. 6 showing another embodiment of the present invention will be described. Like FIG. 5, this is a concrete example of the principle diagram of FIG. 4, and the same parts as in FIGS. 4 and 5 are given the same reference numerals. In addition, 23 indicates a voltage setting transistor, which supplies power to the cut-off adjustment circuit.
V _CC ′ is generally set to be V _CC <V _CC ′, and set to a value larger than the variation width of the CPT cutoff voltage.

17 variable constant voltage sources are push-pull amplifiers.
This is the same circuit format as that used in the AB class bias setting circuit. Shows good constant voltage characteristics over a range from small currents to large currents (several mA to several tens of mA). Regarding the cut-off adjustment means, please refer to the fifth section.
Similar to the figure, the variation amount set by the variable constant power source 17 is added to the CPT drive voltage generated at the terminal 16, and the result is transmitted to the CPT cathode terminal.

A transistor with good high frequency characteristics has a small tolerance for collector loss due to its structure, so it is used at the upper limit of the tolerance. When the amplifiers 9R, 9G, 9B have broadband characteristics, the transistors 3R, 3G,
3B is used at the upper limit of its collector loss.
The collector losses of transistors 3R, 3G, and 3B are
Since it is expressed by V _CC ² /4R _L , under the condition of the same collector loss, as the power supply voltage V _CC decreases, the load resistance value RL can be decreased by the square of the rate of decrease. On the other hand, the cutoff frequency of amplifiers 9R, 9G, and 9B is 1/2πC・R _L (C is the stray capacitance connected in parallel with the load resistors 2R, 2G, and 2B (consisting of the output voltage of the transistor, the cathode input capacitance of CPT, etc.) )
As the power supply voltage V _CC decreases, the amplifiers 9R, 9G, 9
Extend the cutoff frequency of B (i.e. widen the band)
be able to. Therefore, according to the present invention,
Since the power supply voltage V _CC of the drive circuit can be set independently of the CPT cut-off voltage, it is possible to set the power supply voltage V _CC to the minimum voltage necessary for the operation of the drive circuit, and as a result, the cut-off voltage adjustment circuit This can be realized without using transistors, which simplifies the circuit and improves reliability.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the voltage between the CPT cathode and the first grid and the optical output, and Figure 2 shows the relationship between the CPT cathode and first grid voltage and the optical output.
A diagram showing an example of a CPT drive circuit, FIG. 3 is a diagram showing an example of a conventional CPT drive circuit considering broadbandization, FIG. 4 is a diagram showing the principle of the present invention, and FIGS. 5 and 6 2A and 2B are circuit diagrams each showing an embodiment of the present invention. 1: Color cathode ray tube, 16R, 16G, 16
B: Braun tube drive circuit output terminal, 17R, 17
G, 17B: Variable constant voltage power supply.

Claims (1)

[Claims] 1. In each signal path between each cathode of the integrated electron gun color cathode ray tube and each drive circuit, a DC power supply is provided in series with low impedance for AC signals and whose voltage can be adjusted independently of each other. A cathode ray tube drive circuit featuring: