JPH046312Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a beam index type color television receiver.

A beam index type color television receiver consists of three primary color phosphors of red, green, and blue repeatedly arranged in a stripe pattern, and an m/n (m,
When an electron beam emitted from a single electron gun sweeps over a surface consisting of index elements repeatedly arranged in a stripe pattern with a regular relationship (n is a positive integer), the index obtained from the index elements is Pulse the signal to create an index pulse, and convert the index pulse to 1/m.
A control signal with a triplet frequency corresponding to the repetition period of the three primary color phosphors is formed by dividing the frequency into 1 and multiplying by n, and modulating the control signal with a video signal to cause the electron beam to impact a predetermined phosphor. This is a television receiver designed to

(b) Prior Art Before explaining the configuration of the main parts, the conventional method of dealing with the loss and increase of index pulses will be explained.

In other words, when the index pulse is normal, 3
It is sufficient to use the output of the digit counter 9.

If a drop occurs in the index pulse, the phase changes from 120° → 240° → 0° each time the index pulse is missing.
→ Since there is a delay of 120°, the output of ternary counter 9 is
It is sufficient to use the output of Nu → Li → Chi → Nu every time a pulse is missing.

Then, when an increase occurs in the index pulse, the phase changes from 120° → 240° → 0° for each pulse increase.
→120 degrees, so the output of the ternary counter 9 can be used as the output of ri → nu → chi → ri every time the pulse increases.

Incidentally, this increase in the index pulse is detected by comparing the output of the counter 8, which divides the frequency by removing short-period pulses, with the output of the counter 9, which divides the frequency of all pulses, by a comparison circuit 10.

As shown in FIG. 1, the configuration of the main parts in the conventional example is such that an index signal generated from an index element and converted into an electric signal by a photoelectric converter 1 is filtered by a band pass filter 2, and then is filtered by a pulsing circuit 3. The pulse is made into an index pulse.

In order to detect this missing index pulse, the first monostable multivibrator 4 whose time constant T ₁ is selected to satisfy Ti<T ₁ <2Ti with respect to the time constant Ti of the index pulse detects the missing index pulse. Detect.

Specifically, as shown in FIG. 2A, when a dropout (indicated by a dotted line) occurs in the index pulse, the output of the first monostable multivibrator 4 becomes high level in the missing portion as shown in FIG. 2B.

Reference numeral 5 denotes a pulse oscillator that generates a pulse having the same frequency as the index pulse, and is turned on only during the period when a high level is applied from the first monostable multivibrator 4 (see FIG. 2C).

6 is a first ternary counter, and the oscillator 5
Divide the output from 1/3. In addition, the above m and n are m
=3, n=2.

7 is a time constant T ₂ with respect to the index pulse period Ti in order to detect an increase in the index pulse.
is the second monostable multivibrator with Ti/2<T ₂ <Ti.

8 is a second ternary counter that counts the output of the second monostable multivibrator.

9 is the third frequency dividing the index pulse by 1/3.
is a ternary counter.

Under normal conditions when the index pulse does not increase, the outputs of the second and third ternary counters 8 and 9 are both equal, but when there is an increase, the output of the second monostable multivibrator 7 goes to a high level during the increase. In order to hold the output of the second ternary counter 8 and the third
The outputs of the ternary counter 9 do not match.

The third ternary counter 9 outputs index pulses of three phases of 0°, 120°, and 240°, but only one of them is output from the switching circuit 11. .

The decoder 12 selects one of the switches a, b, and c of the switching circuit 11 based on the output from the comparison circuit 10 indicating the number of increased pulses and the output from the first ternary counter 6 indicating the number of missing pulses. A control signal is generated to switch automatically.

As shown in FIG. 2, when five index pulses are missing, the first, second, and
The third outputs Chi, Li, and Nu are compared to before the loss, respectively.
It will be delayed by 240°. On the other hand, the outputs of the decoder 12 are E, H, and G in FIG. When switches a, b, and c of the switching circuit 11 are switched with this output, the second
It can be seen that the index pulses with the same phase are obtained before and after the dropout. In reality, switches a, b, and c are formed with NAND gates, and these NAND gates are used instead of switches a, b, and c.
The output of the gate may be further configured to be applied to one NAND gate.

Even when an increase in index pulses is detected, the switching circuit 11 provides the same phase before and after the increase.

In FIG. 2, R indicates the position of the red phosphor, and G and B indicate the positions of the green phosphor and the blue phosphor, respectively.

The index pulse obtained from the switching circuit 11 is converted into a 3.58MHz carrier by the first mixer 13.
By taking the frequency sum with CW and taking the frequency difference with the color signal Chroma in the next second mixer 14, an index signal whose amplitude and phase are modulated by the color signal is obtained. The index signal subjected to such modulation is added to the luminance signal Y in an adder 15, and is supplied to the cathode ray tube through an amplifier 16.

However, the index pulse repetition period Ti
changes depending on the location on the screen, so the relationship with the time constants T ₁ and T ₂ of the first and second monostable multivibrators collapses, resulting in Ti<T ₁ <2Ti, Ti/2<T ₂ <Ti
If this is no longer satisfied, the phase of the index pulse finally obtained from the switching circuit 11 will be different before and after the dropout or increase, making it impossible to achieve accurate color reproduction.

(c) Purpose of the invention The present invention provides a beam index type color television receiver that can reliably detect omissions and additions regardless of changes in the repetition period of index pulses.

(d) Structure of the invention The invention includes a first monostable multivibrator which has a time constant having a predetermined relationship with the period of the index pulse and detects the omission of the index pulse;
A beam index type color television receiver comprising a second monostable multivibrator having a time constant having a predetermined relationship with the period of the index pulse and detecting an increase in the index pulse. A detection means for detecting the frequency is provided, and the time constants of the first and second monostable multivibrators are controlled by the output of the detection means so as to maintain the relationship between the time constant and the index pulse. It is.

(E) Embodiment In FIG. 3, in which the same parts as in FIG. This is a detection circuit that outputs a control voltage.

The output of this detection circuit 17 is applied to the first and second monostable multivibrators 4 and 7, and acts to change their time constants T ₁ and T ₂ . for example,
As the frequency of the index pulse increases, the frequency of the index pulse increases.
When Ti becomes shorter, the time constants T 1 _and T ₂ of the first and second monostable multivibrators 4 and 7 are made smaller, and when the frequency becomes lower and Ti becomes longer, T _{1 becomes smaller.} , lengthen T ₂ . As a result, Ti
The relationships of <T ₁ <2Ti and Ti/2<T ₂ <Ti are maintained, and the index pulse can be reliably deleted or increased regardless of the frequency change of the index pulse. The detection circuit 17 can be composed of, for example, a frequency discriminator, and the time constants T ₁ and T ₂ can be controlled by providing voltage-responsive variable capacitance diodes in the time constant circuits of the first and second monostable multivibrators 4 and 7. The capacitance value of this diode may be varied by the voltage from the detection circuit 17. Incidentally, if the time constant of the pulse oscillator 5 is also controlled as shown in the embodiment of FIG. 3, the processing of the subsequent circuit becomes more reliable.

(f) Effects of the invention According to the invention, the relationship between the time constants of the first and second monostable multivibrators and the period of the index pulse is always maintained, so it is possible to reliably detect index pulse omissions and increases. This has the effect of realizing correct color reproduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of a conventional beam index type color television receiver, and FIG. 2 is an explanatory waveform diagram thereof. FIG. 3 is a block diagram of the main parts of a beam index type color television receiver embodying the present invention. A... Index pulse, 4... First monostable multivibrator, 7... Second monostable multivibrator, 17... Detection circuit.

Claims (1)

[Claims for Utility Model Registration] A photoelectric converter 1 that converts an index signal generated from an index element into an electrical signal; A pulse generator 3 that converts the index signal from the photoelectric converter 1 into pulses; The index pulse from the circuit 3 is inputted, and in order to detect the omission of the index pulse, a first circuit whose time constant T ₁ is selected as Ti<T ₁ <2Ti with respect to the time constant Ti of the index pulse is used. The monostable multivibrator 4 is inputted with the index pulse, and
In order to detect this increase in the index pulse, a time constant T ₂ is set for Ti around the index pulse.
The second monostable multivibrator 7 is selected such that Ti/2<T ₂ <Ti, and the frequency of the index pulse is detected in order to maintain the relationship between the time constant and the index pulse, and this detection output is used to detect the frequency of the index pulse. Said first and second
A beam index type color television receiver comprising: detecting means 17 for controlling the time constants of monostable multivibrators 4 and 7.