JP2605905B2 - Signal correction device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an R, G, B CRT of a projection type video projector.
The present invention relates to a signal correction device for optimizing the deterioration of the image quality due to the difference in the characteristics and the arrangement by correcting the video signal.

2. Description of the Related Art Conventionally, a projection-type video projector is, as shown in FIG.
R, G, B Three CRTs are arranged horizontally, a lens is attached in front of the CRT, and an image is formed on the front screen. At this time, since the screen is a flat surface, the brightness differs between the end and the center of the image. The brightness of the video from the G and CRTs is symmetrical, but the brightness of the video from the R and B CRTs becomes darker as the distance from the lens increases.

Therefore, in order to cover the above-mentioned disadvantage, the correction is performed by superimposing a sawtooth wave or a hyperbolic waveform on the video signal. FIG. 4 shows the waveform for the above correction. That is, in the CRT 53 of FIG. 3B, the left side of the screen 50 becomes dark.
Therefore, when the sawtooth wave of FIG. 4b is superimposed on the video signal of FIG. 4a, the waveform of FIG. 4c is obtained. The video signal after the blanking signal is superimposed with the positive portion of the sawtooth wave, and becomes brighter. In the latter half, the negative part of the sawtooth wave is superimposed and darkens. When the above signal is projected on the screen 50 of FIG. 3, the brightness of the left and right sides of the image is balanced and a uniform image is reproduced. In addition, the correction waveform of R to the CRT 51 is obtained by reversing the sawtooth wave shown in FIG.

The superposition of the two signals will be described with reference to the circuit of the conventional example shown in FIG. The video signal shown in FIG. 4A is input to the terminal 30 shown in FIG. The video signal is input clamp pulse to the second view of the terminal 31 is clamped to the clamp voltage v ₁ at transistor 3. The clamped video signal is applied to the base of the transistor 18 through the emitter followers of the transistors 4 and 10. The transistors 14, 15, 16, 17 and 19 form a double-balanced differential amplifier. The base of current source transistor 19 added to v ₁ voltage.

The sawtooth wave of FIG. 4b is applied to the differential input terminal 29 of FIG.
Through the capacitor 27 and the resistor 26 and
A voltage v ₂ is applied from 25 and input to the bases of transistors 14 and 17. Resistor 2 at the base of transistors 15 and 16
The voltage v ₂ is also input through 4. As a result, terminal 3
A sawtooth wave from a terminal 29 is superimposed on a video signal input from 0, and a brightness correction signal is obtained as a video signal output from a terminal 28 from the intersection of the resistors 22 and 23 as shown in FIG.

By the way, the three CRTs of R, G, and B emit light according to the magnitude of the video signal, but the three CRTs of R, G, and B do not have the same characteristics. As a result, if an appropriate video signal is added to the R, G, B CRT in order to reproduce white with a signal in a dark place and then the R, G, B signals are amplified and brightened, the color becomes almost green.

Problems to be Solved by the Invention As described above, conventionally, in a projection television using three CRTs of R, G, and B, the left, right, top, and bottom colors of the screen could be made uniform. When the level of the video signal to be added is changed, the same white is greenish white,
It had a problem of becoming reddish white.

The present invention solves the above problems and provides a signal correction device that corrects a video signal so that white having the same color temperature is reproduced over the entire screen even when the level of the video signal applied to three CRTs is changed. The purpose is to do so.

Means for Solving the Problems To solve the above problems, the signal correction device of the present invention has a circuit for clamping a signal with a first voltage, and the clamped signal is input to the base of a first transistor. ,
The emitter of the first transistor is grounded through a resistor and is input to the base of a second transistor which creates the first current source of a double balanced differential amplifier, creating the second current source of the differential amplifier. The base of the third transistor applies a first voltage. The collector of the first transistor is connected to a power supply via a capacitor connected in parallel with the first resistor and the second resistor. From the collector of the first transistor via the emitter follower via a resistor to a pair of bases of the double balanced differential amplifier, and from a second voltage via a resistor, and another correction waveform also via a resistor. input. Another pair of base inputs of the double-balanced differential amplifier are input from the second voltage via a resistor. The output of the double-balanced differential amplifier is taken out from a collector.

Operation The present invention corrects the horizontal and vertical brightness unevenness of the screen when projecting a screen of a projection television using three CRTs of R, G, and B and changes the signal level while changing the signal level. This makes it possible to correct a video signal in which the whiteness of the projection screen is not greenish or reddish.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Figure 1 inputs a video signal before correction from the terminal 30 in the circuit diagram of a signal correcting apparatus according to an embodiment of the present invention, the terminal clamp pulse for clamping the signal to the voltage v ₁
Enter from 31. The video signal clamped by the transistor 3 is impedance-converted by the transistor 10 at the next stage by the emitter follower of the transistor 4 and sent to the transistor 18, while performing inversion amplification. The resistor 8 connected to the collector of the transistor 10 determines the amplification factor of the video signal based on the ratio with the resistor 11. Further, the capacitor 7 connected in parallel with the variable resistor 6 connected to the resistor 8 determines a DC bias, and adjusts the bias of the inverted and amplified video signal generated at the collector of the transistor 10.
The resistor 13 through the emitter follower and a correction waveform such as a sawtooth wave input from the terminal 29 is further supplied with the power supply v ₂ through the resistors 25 and 26 via the capacitor 27, and the inverted and amplified video signal from the resistor 13 is added. The signals are added and input to the bases of the transistors 14 and 17 of the double balanced differential amplifier, and the power supply v ₂ is applied to the bases of the other transistors 15 and 16 via the resistor 24.

The output of the above differential amplifier (transistors 14 to 19)
Although appearing from the resistors 22 and 23, the left and right and up and down brightness on the screen are corrected by a correction signal such as a sawtooth wave as in the conventional circuit, and the video signal and the inverted and amplified signal are superimposed, and the video signal is At a place where the amplitude is large, a non-linear video signal whose amplitude is larger than that of the original video signal is obtained.

Therefore, through the circuit of the present invention, the above-mentioned non-linear video signal is added to the signal inputs of the B and R CRTs, and adjustment is performed by changing the resistor 6 so that the G CRT does not exhibit the non-linear performance.

Advantageous Effects of the Invention According to the present invention, the brightness of the screen projected by the projection type television on the left, right, top and bottom is made uniform and the R, G, B
By making the level of the video signal applied to the CRT non-linear, white does not become greenish or reddish even when the level of the video signal is changed. The above effects can be realized with a very small number of components and performed simultaneously.

[Brief description of the drawings]

1 is a circuit diagram of a signal correction device according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a signal correction device of a conventional example, FIG. 3 is a schematic diagram illustrating the operation of a projection type video projector,
FIG. 4 is a waveform diagram for explaining the operation of the signal correction device. 1,2,7,27 …… Capacitors, 5,6,8,11,12,13,19,20,2,22,
23,24,25,26 …… resistance, 3,4,9,10,14,15,16,17,18,19…
... transistors.

Claims (1)

(57) [Claims] A signal correction device for a projection type video projector for synthesizing images projected from three CRTs of R, G, B arranged in a horizontal direction on a screen, wherein an input image signal is clamped by a first voltage. Clamp circuit, a first transistor to which a clamped signal is input to a base, a first resistor grounding an emitter of the first transistor, an emitter of the first transistor, and the first resistor A second transistor connected to the second transistor and serving as a first current source of the double-balanced differential amplifier; and a third transistor configured to apply the first voltage to the base to create a second current source of the double-balanced differential amplifier. And a means for adding a collector output signal and an input correction signal of the first transistor and applying the added signal to an input of the double-balanced differential amplifier, The collector of one transistor is connected to a power supply via a second resistor and a third resistor connected in series, and a capacitor is connected in parallel with the third resistor. Said three
A signal correction device provided in at least two CRTs at both ends of the CRT, and from the two CRTs, a non-linear video signal is projected onto the screen.