JPS6232874B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The screen size of a color television receiver varies in accordance with variations in the anode voltage supplied to the picture tube and the power supply voltage supplied to the horizontal and vertical deflection systems.

Therefore, in beam index type color television receivers, the screen size changes due to the reasons mentioned above because the colors are switched between red, green, and blue based on the index signal obtained by scanning the electron beam. In other words, if the deflection speed of the electron beam fluctuates, the color switching timing shifts and the colors on the color screen become out of order.

Therefore, in beam index type color television receivers, it is particularly necessary to stabilize the screen size. One possible means of stabilizing this screen size is to use an index signal.

For example, if the deflection speed of the electron beam changes, the frequency of the index signal will also change.
This method detects this frequency fluctuation and controls the power supply voltage of the deflection system.

However, in this method, which uses the index signal itself to discriminate its frequency, frequency discrimination cannot always be performed accurately. That is, since the index signal is created by an electron beam that is density-modulated by the video signal, this index signal contains many noise components that have been cross-modulated by the video signal, etc. Further, when the screen becomes dark, the index signal necessary for control cannot be detected from this part, so frequency discrimination of the index signal cannot always be performed correctly, and control of the screen size becomes unstable.

Therefore, although the present invention attempts to stabilize the screen size by using an index signal, it is devised to prevent the above-mentioned problem from occurring.

An example of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a system diagram of essential parts showing an example of the present invention, in which 1 is a beam index type color picture tube, and a signal So containing an index signal detected by a photodetector 2 is passed through a bandpass filter 3. , and only the index signal Si is separated. The index signal Si is supplied to a beam scanning position detection circuit 10. This detection circuit 10 is composed of a PLL circuit 4 and a counter 5 whose clock is a pulse obtained by this PLL circuit 4.

As is well known, the PLL circuit 4 has a variable oscillator, for example, a VCO 6, whose output is divided by a counter 7 to the basic index signal frequency _fi ,
This frequency-divided output S _I is phase-compared with the index signal Si in a phase comparator 8, and this comparison output is supplied to the VCO 6 as a control voltage through a low-pass filter 9. Therefore, the frequency-divided output S _I becomes an output that is locked to the phase of the index signal Si.

The oscillation frequency of the VCO 6 differs depending on the arrangement format of the index stripes and color phosphor stripes of the color picture tube 1. The oscillation output of the VCO 6 is supplied to a gate pulse forming circuit 11, and this gate pulse is supplied to a color switching circuit 12.
The primary color signals that density modulate the electron beam are switched as desired. That is, when scanning a red color phosphor stripe, a red primary color signal is used, and when scanning a green color phosphor stripe, a green primary color signal is used.
When scanning the blue color phosphor stripe, color switching is performed such that the electron beam is density-modulated using the blue primary color signal.

The frequency-divided output S _I is supplied to the address counter 5 as its clock pulse;
As mentioned above, _I is an output synchronized with the index signal Si, so the counter output is an output corresponding to the horizontal scanning position of the electron beam (beam position output)
becomes. Therefore, by using this beam position output, it is possible to detect a pulse signal related to the scanning time of the electron beam passing between two predetermined points in the horizontal scanning direction.

Note that the address counter 5 is cleared every 1H. 14 is a clear pulse forming circuit,
It is formed based on the index signal Si and a pulse (not shown) obtained when an electron beam scans a predetermined position outside the effective screen.

For example, the distance between two predetermined points is S as shown in FIG.
When is an effective screen, the horizontal scanning section L between one point outside this effective screen (for example, a point on the straight line la) and any point within the effective screen (for example, a point on the straight line lb)
refers to Note that the straight line la corresponds to the first index stripe in this example.

Each of the above points can be detected by monitoring the beam position output, that is, the counter output. First and second comparators 16A and 16B are provided to detect these points. When the electron beam scans on the straight line la, a first output Pn is obtained, and when the electron beam scans on the straight line lb, a second output qn' is obtained (FIG. 4B). Therefore, by setting the flip-flop circuit 17 constituting the beam scanning time detection circuit 20 with the first output Pn and resetting it with the second output qn', the time required to scan the horizontal scanning section L in each horizontal scanning line can be reduced. A pulse signal S _Q (FIG. 4C) corresponding to the time is formed.

Here, since the scanning time of the electron beam differs depending on the deflection speed of the electron beam, if the deflection speed differs, the scanning time of the electron beam required to scan the above-mentioned horizontal scanning section L naturally also differs. Therefore, the pulse width of the pulse signal S _Q varies depending on the deflection speed.

The pulse signal S _Q is a sawtooth signal forming circuit 18
The sawtooth signal (voltage) S _S (fourth
(D), and this sawtooth signal S
_S is supplied to the sampling hold circuit 19,
It is sampled at the rising edge of the second output, and its value is held. The sampling hold output S _H (FIG. 4D) is supplied to, for example, a power supply circuit (not particularly shown) of the horizontal deflection circuit 21 for voltage control, and this power supply voltage is controlled so that the deflection speed is constant. It is.

Therefore, as shown in Fig. 2, the first half of the screen (for example, the section represented by the two horizontal scanning lines l ₁ and l ₂ ) is at the normal deflection speed (normal speed); If a part (for example, an interval, field is the same or different from the interval) is slower than the normal speed, and a later part of the screen (the interval, field is the same or different) is faster, the screen size will change accordingly. do. For example, as shown in Figure 3, the screen size (S
If _I ) is the size of the solid line, then the screen size (S) will be shown by the broken line in the section, and the screen size (S) will be shown by the dashed-dotted line in the section.

However, the sampling and holding output S _H is an output related to variations in screen size, and since the horizontal deflection power supply voltage is controlled by negative feedback with this sampling and holding output S _H , the screen size is always constant.

As described above, according to the present invention, fluctuations in deflection speed can be suppressed, so that the screen size can be stabilized and color switching can be performed accurately. According to the present invention, fluctuations in deflection speed are detected not by using the index signal Si itself obtained by the photodetector 2, but by using the PLL in particular.
Since the frequency-divided output S _I of the circuit 4 is used for detection, the screen size correction operation is stabilized.

In other words, the variable oscillator 6 of the PLL circuit 4 continues to oscillate even if the input level of the index signal Si is weak or even if this index signal Si is not input at all. Even when the beam is blanked, the divided output S _I can always be obtained. Therefore, the screen size can be constantly corrected, and the screen size correction operation is stabilized.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of the main parts showing an example of this invention.
2 and 3 are explanatory diagrams of screen size fluctuations, and FIG. 4 is a waveform diagram for explaining the operation of FIG. 1. 1 is a beam index type picture tube, 10 is a beam scanning position detection circuit, 4 is a PLL circuit, 20 is a beam scanning time detection circuit, 21 is a horizontal deflection circuit, Si
is an index signal, and S _I is a frequency-divided output.

Claims (1)

[Claims] 1. In a beam index type color television receiver, an index signal obtained by scanning an index stripe with an electron beam is transmitted to a PLL.
The electron beam is supplied to a horizontal scanning position detection circuit consisting of a circuit and a counter using the output pulse of this PLL circuit as a clock to obtain a beam position output, and this is supplied to a beam scanning time detection circuit to detect the horizontal scanning direction. A signal related to the scanning time of the electron beam passing between two predetermined points including the effective screen area is detected, and the horizontal deflection power circuit is controlled based on this detection output to stabilize the screen size. A stabilization circuit for the screen size.