JPS6232871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A beam-indexed color television receiver has a single electron beam as a picture tube with horizontally arranged red, green and blue colored phosphor stripes. An index that has a fluorescent surface and index phosphor stripes arranged horizontally on the inner surface of the phosphor surface is used, and is obtained by scanning the index phosphor stripes with an electron beam. Color switching is performed based on the signal, and when the electron beam scans the red color phosphor stripe, the red primary color signal is used.
When scanning a green phosphor stripe, a green primary color signal is used, and when a blue phosphor stripe is scanned, a blue primary color signal is used for density modulation.

Incidentally, the amplitude of the index signal varies greatly depending on the brightness of the screen, that is, the intensity of the electron beam. However, in order to perform stable color switching, it is desirable that the index signal has a constant amplitude. Particularly at the black level, it is necessary to ensure that an index signal of constant amplitude determined by the minimum beam current is obtained so that the screen is completely reproduced.

In order to keep the amplitude of the index signal constant, a method generally considered is to supply the index signal obtained from a photodetector through a bandpass filter to a limiter amplifier with a large gain. However, in this method, a phase shift occurs in the index signal in the limiter amplifier, and a bandpass filter with high Q is required to remove the interference signal, so the group delay time becomes large and the index signal There is an inconvenience that when the frequency of the color changes, the timing of color switching shifts.

It is also possible to supply the index signal to an AGC circuit to maintain a constant amplitude, but in the AGC circuit, it is necessary to detect the amplitude of the index signal and control the amplitude of the index signal using the detected voltage, which increases the control time. This causes a delay, which is not desirable.

Furthermore, a method of dividing the index signal by the cathode current has been considered, but the cathode current is based on switched primary color signals of red, green, and blue and has a high frequency. There is a problem in that it is difficult to implement a division circuit that divides by .

The present invention eliminates these inconveniences and problems and makes it possible to keep the amplitude of the index signal constant.

In this invention, the level of the index signal or the loop gain of the PLL circuit to which the index signal is supplied is controlled by the signal having the maximum value of the three primary color signals.

FIG. 1 shows an example of the picture receiver of the present invention, where 10 is a beam index type color picture tube, and a photodetector 20 is provided on the outside of the funnel.
The output signal of the photodetector 20 is supplied to a bandpass filter 30 to extract an index signal with a frequency determined by the pitch of the index phosphor stripe and the scanning speed of the electron beam. Supplied.

In the PLL circuit 50, the index signal through the amplifier 40 is supplied to the phase comparator 51, the output pulse of the voltage controlled oscillator 52 is supplied to the frequency divider 53 and frequency-divided, and the frequency-divided pulse is transmitted to the phase comparator 51.
The output voltage of the phase comparator 51 is supplied to the oscillator 52 through the low-pass filter 54,
An oscillator 52 produces pulses at a frequency N times that of the index signal, or three times the so-called triplet frequency determined by the pitch of the color phosphor stripe and the scanning speed of the electron beam.

The output pulses of this PLL circuit 50 are supplied to a gate pulse generator 60 consisting of a ring counter, and the three primary color signals of red, green and blue to be gated are regulated by a mode set pulse _PMS .
A gate pulse of the phase is obtained, and this is the gate pulse of the gate circuit 7.
0R, 70G and 70B, the red, green and blue primary color signals E _R , E _G and E _B are sequentially gated, and the switched primary color signals are fed to, for example, the first grid 11 of the picture tube 10. Ru.

Then, the red, green and blue primary color signals E _R , E _G and E _B are supplied to the maximum value detection circuit 80, and as shown in FIG. 2A, among the primary color signals E _R , E _G and E _B The voltage with the highest level is taken out, and this maximum value voltage E _M is supplied to the control circuit 90 to obtain, for example, a control voltage E _C that is inverted with respect to the voltage E _M , and this control voltage E _C is used for gain control. The signal is supplied to the amplifier 40 as a gain control signal. In this case, the larger the voltage E _C is, that is, the smaller the voltage E _M is, the larger the gain is, and the smaller the voltage E _C is, that is, the larger the voltage E _M is, the smaller the gain is. Therefore, an index signal with a constant amplitude is obtained from the gain control amplifier 40. In this way, the gain control amplifier 40
is provided to keep the amplitude of the index signal constant; instead, the control voltage E _C from the control circuit 90 is
is supplied to the phase comparator 51 of the PLL circuit 50,
The gain of the phase comparator 51 may be controlled by the control voltage _E.sub.C. Also in this case, the gain is made larger as the voltage E _C is larger, that is, as the voltage E _M is smaller, and the gain is smaller as the voltage E _C is smaller, that is, as the voltage E _M is larger. Therefore, this is equivalent to supplying an index signal of constant amplitude to the phase comparator 51 of the PLL circuit 50.

Also, the gain of the phase comparator 51 is controlled.
Instead of controlling the loop gain of the PLL circuit 50, a gain control amplifier is provided between the phase comparator 51 and the low-pass filter 54 or between the low-pass filter 54 and the oscillator 52, and its gain is controlled by the control voltage E _C. The loop gain of the PLL circuit 50 may be controlled.

Furthermore, as in the example in the figure, the gain control amplifier 40
may be provided to control the level of the index signal, and at the same time, the loop gain of the PLL circuit 50 may be controlled by controlling the gain of the phase comparator 51, for example.

FIG. 3 shows a maximum value detection circuit 80 and a control circuit 90.
In the specific example of the gain control amplifier 40, the maximum value detection circuit 80 has a common emitter resistor 84 connected to the emitters of transistors 81, 82, and 83, and primary color signals E _R , E _G and E _B are supplied, so that one of the transistors 81, 82 and 83 is always on and the other two are off, so that the above-mentioned maximum voltage E _M is taken out at the common connection point of the emitters. It's getting old.

In the control circuit 90, this maximum voltage E _M is supplied to the base of a transistor 92 via a resistor 91, and a load resistor 93 is supplied to the collector of the transistor 92.
is connected, and a control voltage E _C which is inverted with respect to the voltage E _M is obtained at its collector, which is taken out through a buffer transistor 94. Here, a transistor 96 is connected to the emitter of the transistor 92 via a variable resistor 95 for gain adjustment, and a voltage adjusted by a variable resistor 97 is supplied to the base of the transistor 96, so that the maximum voltage E _M When the voltage is below a certain threshold voltage V _T , transistors 92 and 96 are turned off, and the control voltage E _C becomes the power supply voltage +Vcc, as shown in FIG. be done.

In addition, in the picture tube 10, an index phosphor stripe is also provided at the horizontal scanning start part on one side of the effective screen area provided with the color phosphor stripe, and a constant beam current flows at this horizontal scanning start part. When a mode set is performed by counting the index signal at the horizontal scanning start point, for example, the load resistor 93 and the transistor 92
The collector and emitter of a transistor 99 are connected in parallel to the series circuit of the collector and emitter of the transistor 99, and a pulse is applied to the base of the transistor 99 to cause a constant beam current to flow at the start of horizontal scanning, as shown in FIG. 2B. P _W is supplied, and at the beginning of the horizontal scan, transistor 99 is turned on, and therefore transistor 92 is turned off, as shown in FIG.
As shown by the broken line, the control voltage E _C becomes the power supply voltage +Vcc, so that the gain of the amplifier 40 is maximized.

The gain control amplifier 40 has a differential amplifier configuration, that is, transistors 41 and 42
and a transistor 43 constituting the constant current source,
It consists of a diode 44, a resistor 45, and load resistors 46 and 47. An index signal S _IO from a bandpass filter 30 is supplied between the bases of transistors 41 and 42, and a control voltage E _C
The current of the constant current source is changed to control the gain, and the index signal G _IX is taken out as a balanced output from the collectors of the transistors 41 and 42, and is supplied to the phase comparator 51 of the balanced input of the PLL circuit 50. It's getting old. Since it is a balanced output, the component of the control voltage E _C does not appear in the output.

FIG. 4 shows a specific example of the phase comparator 51 in the case where the gain of the phase comparator 51 of the PLL circuit 50 is controlled. It consists of a transistor 107, a diode 108, and a resistor 19 constituting a source, and load resistors 111 and 112, and capacitors 121, 122 and a resistor 123 are connected between the collectors of transistors 101 and 103 and the collectors of transistors 102 and 104.
An index signal _SIO from the bandpass filter 30 or an index signal G from the gain control amplifier 40 is connected between the bases of the transistors 101 and 104 and the bases of the transistors 102 and 103.
_IX is supplied, the output pulse S _N of the frequency divider 53 is supplied between the bases of the transistors 105 and 106, the current of the constant current source is changed by the control voltage E _C and the gain is controlled, and the gain of the voltage controlled oscillator 52 is controlled. A control voltage is tapped off at a balanced output.

Note that even in the case where the index signal is supplied to a frequency multiplier composed of a tuning circuit or the like instead of a PLL circuit, a gain control amplifier may be inserted in the index signal system to control the gain.

As described above, according to the present invention, since control is performed using the maximum value signal of the three primary color signals,
Unlike when an AGC circuit is provided, there is no time delay in control, and the maximum value signal has a low frequency, so control is easy and easy to implement. Also,
Even when the index signal is supplied to a limiter, the limiter may have low capability, and almost no phase shift of the index signal occurs in the limiter.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an example of the receiver of the present invention, Fig. 2 is a waveform diagram for explaining the same, Figs.
The figure is a connection diagram of a specific example of the main parts. 20 is a photodetector, 30 is a bandpass filter,
40 is a gain control amplifier, 50 is a PLL circuit, 51 is a phase comparator thereof, 80 is a maximum value detection circuit, and 90 is a control circuit.

Claims (1)

[Claims] 1 Detect the maximum value of the three primary color signals supplied to the beam index type color picture tube, and use this detection output to determine the gain or PLL of the amplifier to which the index signal obtained from the color picture tube is supplied.
A beam index type color television receiver in which the amplitude of the index signal is kept constant by controlling the loop gain of the circuit.