JP2670102B2 - Video signal processing circuit in projection TV - Google Patents

Description

TECHNICAL FIELD The present invention relates to a video signal processing circuit in a projection TV, and more particularly to a video signal processing circuit suitable for use in a liquid crystal projection TV.

BACKGROUND ART In a three-tube color projection TV, images projected on three projection tubes coated with red (R), green (G), blue (B) and monochromatic phosphors are projected onto a screen using a projection lens. An image is formed. By arranging three projection tubes in the horizontal scanning direction of the display screen, as shown in FIG. 5, the R and B optical axes are perpendicular to the screen surface (G optical axis). ), The trapezoidal distortion occurs in a shape having the top and bottom sides in the horizontal scanning direction of the display screen.

For this reason, conventionally, the color shift due to the trapezoidal distortion is corrected by displaying the screen after the trapezoidal distortion correction on each of the R and B projection tubes using a convergence circuit as shown in FIG. . That is, for each of the R and B projection tubes, in addition to the main deflection yoke, a sub deflection yoke 61 for correction is used.
R, 61B are provided, and a predetermined waveform signal emitted from the convergence waveform generator 62 is level-adjusted by the level adjustment circuits 63R, 63B, and then applied to the sub deflection yokes 61R, 61B via the power amplifiers 64R, 64B. By passing a current through them, a screen with the trapezoidal distortion corrected is projected on each of the R and B projection tubes.

By the way, although there is a projection TV using a liquid crystal light valve, the trapezoidal distortion described above cannot be avoided even in this liquid crystal projection TV. However, in a liquid crystal projection TV in which pixel cells are arranged in a grid as shown in FIG. 7, a trapezoidal distortion corrected screen is projected on a light valve. However, since the display screen has a trapezoidal shape with the top and bottom sides in the horizontal scanning direction, diagonal scanning is required, which makes it very difficult to scan the screen.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a video signal processing circuit in a projection TV that can easily correct trapezoidal distortion even when a light valve in which pixel cells are arranged in a grid in advance is used. The purpose is to do.

The video signal processing circuit according to the present invention outputs a digitized video signal in a projection TV in which the optical axis of the projection lens is tilted by a predetermined angle in the vertical scanning direction of the display screen with respect to the axis perpendicular to the screen surface. A storage means capable of sequentially storing an amount corresponding to 1H (H: horizontal scanning period), a means for generating a clock synchronized with a synchronizing signal included in a video signal and using the clock as a writing clock of the storage means, and constant for every predetermined H A means for generating a clock whose frequency changes by frequency and using the clock as a read clock of the storage means; and a means for controlling the timing of reading stored information from the storage means while changing the read time at predetermined intervals of a predetermined time interval. The frequency and the fixed time are set according to the inclination angle of the optical axis of the projection lens.

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

In FIG. 1 showing, for example, the configuration of a liquid crystal projection TV using three projection lenses according to the present invention, each of projection lenses 1R, 1G, 1B of R, G, B is arranged in a vertical direction with respect to a screen 2, that is, a display. The optical axes of the upper and lower projection lenses 1R and 1B are inclined by an angle θ with respect to the optical axis of the projection lens 1G perpendicular to the screen surface. By these projection lenses 1R, 1G, 1B, an image by the optical system described below is enlarged and projected on the screen 2, but since the configuration of each optical system is the same, only the optical system of the projection lens 1G is used. It is shown.

The projection light emitted from the projection light source 3G as diffused light is converted into parallel light by the condenser lens 4G and applied to the liquid crystal light valve 5G. The light that has passed through the liquid crystal light valve 5G is transmitted through the half mirror 6G and is enlarged and projected by the projection lens 1G, so that the image written in the liquid crystal light valve 5G is enlarged and displayed on the screen 2.
An image corresponding to the input video signal is written in the liquid crystal light valve 5G.

Here, when each optical axis of the projection lenses 1R and 1B is incident at an angle of θ with respect to an axis perpendicular to the screen surface, a trapezoidal distortion occurs in which the top and bottom sides are in the vertical scanning direction of the display screen. Therefore, it is necessary to write a screen on which the trapezoidal distortion is corrected on the liquid crystal light valves 5R and 5B in these optical systems. Therefore, the projection lens 1R, 1
The liquid crystal light valves 5R and 5B in each optical system B are input with the video signal after the trapezoidal distortion correction process.

FIG. 2 is a block diagram showing an embodiment of a video signal processing circuit according to the present invention for performing trapezoidal distortion correction processing.
In the figure, a video signal is supplied to an A / D converter 11 and a sync separation circuit 12. The video signal digitized by the A / D converter 11 is supplied to the line memory 13. The sync separation circuit 12 separates and extracts the horizontal sync pulse (Hsync) and the vertical sync pulse (Vsync) contained in the video signal. The PLL circuit 14 as a first clock generation means generates a clock of, for example, 4 fsc (fsc is a color subcarrier frequency) in synchronization with the horizontal synchronization pulse, and writes the sampling clock of the A / D converter 11 and the writing of the line memory 13. Supply as a clock. The write control circuit 15 supplies a write enable signal synchronized with the horizontal sync pulse to the line memory 13.
The line memory 13 sequentially responds to the write enable signal,
The digitized video signal is stored by the write clock in an amount corresponding to 1H (H: horizontal scanning period).

On the other hand, an H counter 16 that counts horizontal synchronizing pulses is provided, and the H counter 16 is reset by the vertical synchronizing pulse. The read control circuit 17 is for generating a read enable signal to the line memory 13, and is given for every predetermined H based on the count output of the H counter 15, for example, by M (integer) times the pulse width of the write clock. The timing of reading the stored information is controlled by changing the generation timing of the read permission signal for each fixed time.
In addition, the PLL that generates the read clock of the line memory 13
The circuit 18 is provided as the second clock generating means. The PLL circuit 18 has a frequency divider whose frequency division ratio N is variable. The frequency division ratio N is variably controlled by a constant value every predetermined H by the frequency division ratio control circuit 19, so that the frequency It generates a read clock whose frequency (N × 15.75 KHz) changes by a constant frequency. The fixed time in the read control circuit 17 and the fixed frequency in the PLL circuit 18 have a correlation with each other, and are set according to the inclination angle θ of each optical axis of the projection lenses 1R and 1B with respect to the axis perpendicular to the screen surface. Line memory
The digitized video signal read from 13 is converted into an analog signal by the D / A converter 20, and the projection lens 1 shown in FIG.
It becomes the input video signal of the liquid crystal light valves 5R and 5B in each of the R and 1B optical systems.

 Next, the circuit operation of such a configuration will be described.

First, in the PLL circuit 14, 4
A write clock of fsc is generated, and in response to a write enable signal issued from the write control circuit 15, a digitized video signal corresponding to 1H is sequentially stored in the line memory 13 by the write clock.

On the other hand, the read control circuit 17 generates a read enable signal in which the generation timing is delayed (or advanced) by a predetermined time for each predetermined H based on the count output of the H counter 16, and
The PLL circuit 18 is controlled to a predetermined H by the control of the division ratio control circuit 19.
The frequency division ratio N is incremented (or decremented) every time, so that a read clock whose frequency is increased (or decreased) by a constant frequency is generated for each predetermined H.

Here, if N = 288, for example, the first data captured in the line memory 13 by the write clock having a constant frequency of 4 fsc.
The data of 1H will be read from the line memory 13 by the read clock of almost the same frequency 4fsc. In the next 1H, assuming that N = 289, the frequency of the read clock increases, so that the video signal output via the D / A converter 20 is compressed on the time axis, and at the same time, the generation timing of the read enable signal Also, the start position of the video signal is also delayed by delaying for a certain time.

In this way, the read timing is delayed by a predetermined time for each predetermined H, and the frequency of the read clock is set to the predetermined H.
By sequentially increasing the fixed frequency by a constant frequency and sequentially compressing the video signal corresponding to 1H on the time axis, it is possible to obtain a screen as shown in FIG. 3B from a normal screen as shown in FIG. In addition, the reverse operation, that is, the read timing is advanced by a predetermined time every predetermined H from a state where the read timing is set late, and the frequency of the read clock is lowered by a predetermined frequency every predetermined H, whereby a video signal equivalent to 1H is timed. By gradually expanding the time axis from the axially compressed state, it is possible to obtain a screen as shown in FIG. 3C from a normal screen as shown in FIG.

Therefore, the constant time for delaying the read timing for each predetermined H and the constant frequency for increasing the frequency of the read clock for each predetermined H are set to be inclined with respect to the axis perpendicular to the screen surface of each optical axis of the projection lenses 1R and 1B in FIG. By setting according to the angle θ, the trapezoidal distortion can be corrected, and the screen with the trapezoidal distortion corrected can be written on the liquid crystal light valve. At this time, since the scanning direction on the liquid crystal light valve coincides with the direction of the lattice of the liquid crystal cell as shown in FIG. 3, it is possible to use the liquid crystal light valve in which the liquid crystal cells are arranged in a lattice beforehand. Even if there is, screen scanning can be performed easily.

In addition, in the above-described embodiment, the case where the present invention is applied to the correction of the trapezoidal distortion in the liquid crystal projection TV using three projection lenses has been described. However, as shown in FIG.
In a liquid crystal projection TV in which B is enlarged and projected by one projection lens 1, the invention can be applied to correction of trapezoidal distortion generated when the screen 2 and the optical axis of the projection lens 1 are not perpendicular in the vertical scanning direction of the display screen. . Further, the present invention is not limited to the liquid crystal projection TV, but can be applied to all projection TVs using light valves in which pixel cells are arranged in a grid in advance.

Further, in the above-mentioned embodiment, the fixed time and the fixed frequency are fixed after the constant setting of 1 degree, but it is also possible to manually set these, and according to this, the projection side and the screen are separated. In the case of the above system, it is convenient that the above-mentioned constant time and constant frequency can be adjusted according to the inclination angle θ of the optical axis of the projection lens with respect to the axis perpendicular to the screen surface.

Effects of the Invention As described above, according to the present invention, at the time of reading recorded information from a line memory, the read timing is changed by a predetermined time every predetermined H, and the frequency of the read clock is changed every predetermined H. By changing the constant frequency and the constant time and the constant frequency according to the inclination angle of the optical axis of the projection lens with respect to the axis perpendicular to the screen surface, trapezoidal distortion can be corrected and the scanning direction can be changed in the horizontal scanning direction. Therefore, even when using the light valve in which the pixel cells are preliminarily arranged in a lattice pattern,
The trapezoidal distortion can be easily corrected.

[Brief description of the drawings]

FIG. 1 is a block diagram of a liquid crystal projection TV using three projection lenses according to the present invention, FIG. 2 is a block diagram showing an embodiment of a video signal processing circuit according to the present invention, and FIG. 3 is a normal screen (a). FIGS. 4A and 4B show screen shapes of correction screens (b) and (c), FIG. 4 is a configuration diagram of a liquid crystal projection TV using one projection lens, FIG. FIG. 6 is a block diagram of a convergence circuit for correcting color misregistration due to trapezoidal distortion, and FIG. 7 is a diagram showing a screen scan according to the present invention for a liquid crystal light valve in which liquid crystal cells are arranged in a grid pattern. Explanation of Signs of Main Parts 1,1R, 1G, 1B ... Projection Lens 2 ... Screen 5,5R, 5G, 5B ... Liquid Crystal Light Valve 13 ... Line Memory 14,18 ... PLL Circuit 15 ... Write Control Circuit 17 …… Readout control circuit 19 …… Division ratio control circuit

Claims (2)

(57) [Claims] 1. A video signal processing circuit in a projection TV in which an optical axis of a projection lens is tilted by a predetermined angle in a vertical scanning direction of a display screen with respect to an axis vertical to a screen surface, which is a digitized video. Storage means capable of sequentially storing signals corresponding to 1H (H: horizontal scanning period), and a first clock for generating a clock synchronized with a synchronization signal included in the video signal and using the clock as a writing clock of the storage means. Generating means, second clock generating means for generating a clock whose frequency changes by a constant frequency for each predetermined H to be a read clock of the storage means, and a timing for reading stored information from the storage means every predetermined H. And a control means for controlling while changing the time by a fixed time, wherein the fixed frequency and the fixed time are set according to the inclination angle of the optical axis. Oh signal processing circuit. 2. The video signal processing circuit according to claim 1, wherein the projection TV is a liquid crystal projection TV having a liquid crystal light valve in which liquid crystal cells are arranged in a lattice pattern.