JPS62123886A - Convergence circuit - Google Patents

Abstract

PURPOSE:To utilize the dynamic range of a driving circuit to the utmost at all times by adjusting the DC component of a current flows in a convergence yoke so as to go to zero by a signal that detected presence of a scanning point at the center of a picture. CONSTITUTION:Signals for correcting convergence is made by an analog waveform generator 1, and supplied to a clamping circuit 2. The clamping circuit 2 is a circuit that fixes to specified potential at every clamping pulse supplied from a timing generator 5. Signals from which DC component is removed are supplied from the clamping circuit 2 to a driving circuit 3 as convergence correction signals. Here, the timing generator 5 produces clamping pulses corresponding to the timing when a scanning point is positioned at the center of a picture from horizontal synchronizing signals HD and vertical synchronizing signals VD, and thereby, correction current is adjusted to go to zero at the center of the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a convergence circuit, and particularly to a convergence circuit for a multi-tube video projector.

(2) Conventional technology Conventionally, devices have been known that obtain "one color image" by superimposing images made by CRTs that emit light in red, green, and blue colors.Today's video projectors −
In most cases, this method is used. In this way, when one image is composed of multiple CRTs, each CRT
A convergence yoke is provided independently of the deflection yoke in order to correct the geometric distortion of the image produced by the yoke.

A direct current for correcting a positional shift at the center of the image and an alternating current for correcting distortion at the periphery of the image are passed through the convergence yoke. Correction using direct current is called static convergence correction, and correction using alternating current is called dynamic convergence correction.

As the definition of video projectors has become higher, this convergence correction is also required to be more precise, and a signal generation circuit that can minutely change the correction current required for dynamic convergence correction is needed. has become necessary. For this purpose, analog convergence circuits that divide the screen into several parts and superimpose various waveforms to create signals, and digital convergence circuits that configure the waveform generation circuit with digital circuits have been adopted as signal generation circuits. There is. In either circuit, the drive circuit that drives the convergence yoke requires a wide dynamic range.

(3) Problems to be Solved by the Invention Since such a convergence circuit generates a complicated waveform, a DC component may be superimposed on the current for dynamic and convergence correction. In such a case, as shown in Figure 4, the correction current may exceed the dynamic range D1 of the drive circuit, and as a result, the convergence correction is not performed in the portion that exceeds the dynamic range D (the shaded area in Figure 4). There are problems in that it becomes difficult or impossible to correct.

(4) Means for solving the problems The present invention has been made in view of the above points, and aims to effectively utilize the dynamic range of the drive circuit that drives the convergence yoke, and achieves this purpose. In order to do this, we need a detection means to detect that the scanning point is in the center of the screen, and a magnitude of the DC current so that the DC component of the correction current flowing through the convergence yoke is zero when there is a detection output from the detection means. and an adjusting means for adjusting.

(5) Effect In this configuration, since the output of the adjustment means is supplied to the drive circuit, the dynamic range of the drive circuit can always be utilized to the maximum extent.

(6) Examples Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a block diagram showing one embodiment of a convergence circuit according to the present invention.

In FIG. 1, a signal for convergence correction is generated by an analog waveform generator 1 and is supplied to a clamp circuit 2. The clamp circuit 2 may be a well-known clamp circuit, for example connected to an analog waveform generator l via a capacitor.
The output of the capacitor is supplied to the drive circuit 3, and one end of this capacitor is fixed to a predetermined potential for each clamp pulse supplied from the timing generator 5. The drive circuit 3 amplifies the convergence correction signal supplied from the clamp circuit 2 after removing the DC component, and supplies the amplified convergence correction signal to the dynamic convergence yoke 4 .

The timing generator 5 generates a timing signal with a predetermined period from the horizontal synchronization signal HD and the vertical synchronization signal VD, supplies it to the analog waveform generator l, and also outputs it to the clamp circuit 2 at a timing corresponding to when the scanning point is located at the center of the screen. Supply clamp pulse. Timing generation 'Js5 is
For example, it is composed of a mono multivibrator triggered by a horizontal synchronizing signal HD or a vertical synchronizing signal VD. The reason why the clamp pulse is supplied to the clamp circuit 2 at the timing when the scanning point corresponds to the center of the screen is that convergence correction is unnecessary at the center of the screen and should be zero, and this is used as a reference. It depends.

FIG. 2 is a block diagram showing another embodiment of the convergence circuit according to the present invention. In the figure, the same reference numerals are given to the same components as in FIG. 1, and explanations thereof will be omitted.

In this embodiment, a signal for convergence correction is generated by a digital circuit. The signal source is a digital waveform generator 12, and the digital waveform generator 12 is a CPU
Waveforms are generated according to commands from I. A clamp pulse is supplied from the timing generator 5 to this digital waveform generator 12, and when a clamp pulse is sent at a timing corresponding to when the scanning point is located at the center of the screen, the digital waveform generator 12 generates the next signal. perform an action.

That is, the dynamic range of the drive circuit 3 is rooo
ooooo (binary)" to rl 1111111 (2
The center value of tear is r'10000000 (binary).
If the signal level commanded by the CPU II to be generated when the clamp pulse is sent is, for example, "1o101110 (binary)", subtract "roolollo (binary)". and forcibly clamp it to the median value rl 0000000 (binary).

After that, until the next clamp pulse is sent, CP
From the signal level commanded by UII, “o.

A signal with a level subtracted by "101110 (binary)" is supplied to the drive circuit 3.

The outputs of the clamp circuit 2 shown in FIG. 1 and the digital waveform generator 12 shown in FIG. 2 described above become a convergence correction signal C from which the DC component has been removed, as shown in FIG.

(7) Effects of the Invention As explained above, the present invention includes a detection means for detecting that the scanning point is at the center of the screen, and a current flowing through the convergence yoke when there is a detection output of this detection means. Since the adjustment means adjusts the magnitude of the DC current so that the DC component becomes zero, a correction current with the DC component removed is supplied to the dry 1 circuit that drives the convergence yoke, and the dynamic range of the drive circuit is reduced. can always be used to its maximum potential.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the convergence circuit according to the present invention, FIG. 2 is a block diagram showing another embodiment of the convergence circuit according to the present invention, and FIG.
4. Waveform diagram explaining the operation of the circuit shown in FIG.
The figure is a waveform diagram illustrating the operation of a conventional convergence circuit. l...Analog waveform generator 2...Clamp circuit 3...Drive circuit 4...Dynamic convergence yoke 5...Timing generator 11...CPU 12...Digital waveform generator Patent applicant NEC Home Electronics Co., Ltd. Agent Patent Attorney Yama 1) Takeki No. 11! 1 No. 20 M3 Figure Center of the screen No. 4 No. 11-1111111

Claims (1)

[Claims] In a convergence circuit for supplying a correction current to a convergence yoke, there is a detection means for detecting that the scanning point is at the center of the screen, and a DC component of the correction current becomes zero when there is a detection output from the detection means. and a convergence circuit for adjusting the magnitude of the correction current.