DE3916055A1 - Avoidance to line jump moire pattern in high resolution TV - using additional detection coil system to provide parallel directions - Google Patents

Abstract

A high resolution television receiver system operates with a horizontal line scan from a triagnular or sinusoidal signal that is controlled to prevent a distortion resulting from a line jump Moire fringe effect. The effect is avoided by using an additional coil pair for deflection control that ensures that the scanning beams are parallel to each other (ES). The field direction is dependent upon the current direction and results upon down deflection of the beam. ADVANTAGE - Avoids distortion in line scan process.

Description

In future HDTV devices with higher deflection frequencies compared to the current standard, for technical reasons you will depart from the known line deflection with different times for line return and return and choose a so-called sine or triangular deflection. In these systems, the electron beam is guided across the screen at approximately the same speed during the run-in and run-back. The vertical grid then creates the desired grid on the screen. Figure 1a shows a grid with triangular deflection without interlacing, while Figure 1b shows one with interlacing. The image information is proportional to the distraction either read from a memory circuit or broadcast by the broadcaster in a future HDTV standard.

The comparison of pictures 1a and 1b with picture 1c, which shows a grid according to today's television standard, shows that the lines in HDTV viewing are not parallel. The result is that a "line jump moir" appears across the width of the screen, but this runs counter to the claim of an HDTV system to deliver the highest reproduction quality. One must therefore try to bring the spacing between the individual lines to a uniform value ( Figure 1d).

The vertical deflection can be used for this purpose because of the frequency response Vertical deflection coils are not used because of the alternating magnetic field cannot be generated due to the high frequency required. The circuit presented here for patent application provides a remedy. they consists essentially of a raster correction circuit and a to additional vertical deflection unit.  

This deflection unit consists, for. B. from two coils attached to the side of the picture tube neck. They are connected in series so that the magnetic field lines of both coils have the same direction when there is a current flow ( Figure 2). The electron beam (ES) hurrying through the picture tube neck is deflected upwards or downwards depending on the direction of the current and the resulting field direction. By means of a sawtooth-shaped current (with triangular deflection) through these deflection coils, it can now be achieved that the lines run parallel and the interfering interlacing moir is canceled ( Fig. 1d).

Since the required deflection angles are very small for this application, can with small inductances and therefore with small deflection currents and - voltages are worked. This results in a control circuit which with a small operating voltage (20 V) the desired fast Change in deflection current reached.

The drive signal for the deflection circuit can be obtained in various ways. For example, a sawtooth generator (with triangular deflection) can be synchronized by pulses from the transmitter (in the event of a possible future HDTV standard) or by pulses from the memory circuit. It is more advantageous, however, to generate the drive signal directly in the image memory circuit in proportion to the readout. Figure 3 shows one possibility of such a circuit. In this case, the control signal is generated in the image memory circuit. It passes through an amplifier on the deflection coils. A negative feedback signal, which is used for linearization, is obtained at the resistor in series with the coil, and is also passed to the amplifier input. This measure ensures that the deflection current (and thus the deflection field) exactly follows the control signal.

With a suitable choice of the control signal in amplitude and curve shape can now be achieved that the lines run parallel on the screen and therefore no annoying interlaced moir 'occurs.

Claims (1)

Process for eliminating the interlaced moir in high-definition television standards with triangular or sine deflection without return (HDTV) characterized by the use of a raster correction circuit in conjunction with an additional deflection coil pair , which serves to deflect the visible lines in parallel.