JPH01318355A - Television receiver - Google Patents

Abstract

PURPOSE:To eliminate the blanking disturbance by switching the frequency characteristic of a video signal amplifying circuit so that its band in the horizontal scanning time is wider than that in the horizontal flyback time. CONSTITUTION:A horizontal blanking pulse applied to a blanking circuit 30 is divided by resistances 2 and 3 and passes a speed up capacitor 1 to switch a transistor TR 5. A capacitor 7 connected to the collector of the TR 6 performs the integral action together with a resistance 32 only in the horizontal flyback time of an R signal. While the TR 5 is turned on, the leading edge is made wider than the horizontal blanking time by the speed up capacitor 1 and the trailing edge is made wider than that by increasing the extent of base drive of the TR 5 to use the delay from switching-on to switching-off. Thus, higher harmonics generated in leading and trailing edge parts of blanking pulses are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal amplification circuit in a television receiver or the like.

BACKGROUND OF THE INVENTION In recent years, television receivers are becoming larger in screen size and in higher image quality. In particular, the improvement in horizontal resolution is remarkable. Recently, double-density television receivers have been developed by making full use of digital technology (memory).

This is a 525-line non-interlaced system in which the signal and scanning speed are doubled compared to the conventional 525-line interlaced scan.

An example of the conventional television receiver mentioned above will be described below with reference to the drawings.

FIGS. 3 and 4 show a block diagram of a conventional double-density television receiver and an example of a video signal amplification circuit. In Figure 3, 2o is anti-f (ANT)
, 21 is a t--j-, 22id VIF circuit,
Receive the broadcast radio waves and obtain the video signal of the desired channel. 23 is a low pass filter (LPF), 24
is an analog/digital converter (A/D), 25 is a memory, 26 is a digital/I//analog converter (D/A), 2
7 is a low pass filter (LPF) for doubling the speed of the video signal in order to perform 525 non-interlaced scans. This is done by writing the signal converted into a digital value by the A/D converter 24 into the memory 25 at the sampling frequency of the clock frequency fW, and reading it out at the sampling frequency of the clock frequency fR, so that the relationship between fW and fR becomes 2fw=fR. This is done by doing. In other words, the low-pass filter 23 and U27 are for preventing aliasing noise generated in the A/D converter 24 and the D/A converter 26, and their characteristics are based on the frequencies shown in each block. Amplitude characteristics are common.

28 is a video signal amplification circuit, and 29 is a cathode ray tube (CRT). The video signal amplification circuit 28 adds a blanking pulse to the doubled speed signal and amplifies it to the amplitude necessary to drive the CRT 29 (more than 100 volts with a gain of about 50 times). Furthermore, the frequency characteristic has a band that is more than twice as large as that of a 525-line interlane television receiver (at least the cutoff frequency, fR or more).

FIG. 4 shows an example of the video amplification circuit 28 in FIG.
A transistor 41 constitutes an R signal preamplifier circuit. 42 to 44 are resistances.

45 is a capacitor, 46 and 47 are diodes.

Reference numerals 48 to 51 indicate transistors, which constitute an R signal main amplifier circuit.

52 is a power supply for the R signal preamplifier circuit, 53 is a power supply for the R signal main amplifier circuit, and 54 is a DC bias power supply that is added to the pace of the transistor 49.

Note that the preamplifier and main amplifier for the G signal and B signal have the same circuit configuration as that for the R signal, so their description in the drawings is omitted.

Problems to be Solved by the Invention However, the above configuration has the problem that blanking interference occurs and vertical line interference occurs in the center of the screen, making it extremely difficult to see. The reason why this blanking interference occurs will be explained with reference to the waveform diagram in FIG. 2. In Figure 2, A is normal/L/R
The signal waveform, B is a double speed R signal waveform, and C is a blanking pulse. - The dotted line signal portion (horizontal blanking period) of the double-speed R signal waveform is blanked by the blanking pulse C as shown by the solid line by the blanking circuit 30 in FIG.

This double-speed R signal waveform is amplified several times by the preamplifier circuit in Figure 4, and several tens of times by the main amplifier circuit5. It has excellent frequency characteristics, and its amplitude is always in the range of several tens of volts to several hundred volts. Therefore, harmonics are generated at the rising and falling edges of this planking pulse, and they flow into the RF input cable of the television receiver, the tuner 21° VIP 22, etc., and enter the stages before A/D conversion. The blanking disturbance shown by ■ in the normal/L/R signal waveform in FIG. 2 further appears as a disturbance at the position shown by ■ in the double speed R signal waveform.

For these reasons, it has been desired to develop a television receiver that has excellent frequency characteristics and a video signal amplification circuit that does not cause interference.

In view of the above-mentioned problems, the present invention has been developed to amplify a desired signal while sufficiently maintaining its frequency band, and to prevent unnecessary blanking interference caused by this excellent frequency characteristic. The object of the present invention is to provide a television receiver having an image signal amplification circuit.

Means for Solving the Problems 66. In order to solve the above problems, the television receiver of the present invention is provided with a video signal amplification circuit, and the frequency characteristics of the video signal amplification circuit are adjusted to the horizontal retrace period. The configuration is equipped with a control circuit that switches to a wide band during the middle and horizontal scanning periods.

Effect of the Invention With the above-described configuration, the present invention provides a wide frequency characteristic with a desired signal frequency band only in the horizontal scanning period, and eliminates the horizontal retrace period, especially the horizontal retrace line, which is a cause of unnecessary blanking interference. Since the rising edge/falling edge 9 portion of the erasing signal has a narrower frequency characteristic than the first frequency band, it is possible to display a video signal without unnecessary blanking interference.

Embodiment Hereinafter, a television receiver according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit diagram of a video signal amplification circuit for a television receiver according to an embodiment of the present invention. In FIG. 1, 1 is Speed Asopco 7, -.

2 to 4 are resistors, 5 is a transistor, 6 is a diode, and 7 is a capacitor. Other parts having the same functions as those in FIG. 4 are given the same numbers and their explanations will be omitted.

The operation of the video signal amplification circuit of the television receiver configured as described above will be explained below. First, the horizontal blanking pulse applied to the blanking circuit 3o is
The resistance is divided by resistors 2 and 3, and the transistor 6 is switched via the speed amplifier capacitor 1. A capacitor 7 connected to the collector of the transistor 5, together with a resistor 32, performs an integrating operation only during the horizontal retrace period of the R signal. The diode 6 is operated as an AC diode during the on period of the transistor 5.

Note that since the on-period of the transistor 50 is wider than the horizontal blanking period performed by the blanking circuit 3o, the leading edge of the horizontal blanking pulse is connected to the speed amplifier capacitor 1, and the outer edge is connected to the base voltage of the transistor 5. It is secured by seeing the amount of life exceed and using the delay from switching on to off.

Although only the R signal system has been described, the horizontal retrace period frequency characteristic switching circuit shown by the broken line in FIG. 1 is also required for the G and B signals.

As described above, according to this embodiment, by switching to narrow the frequency characteristics only during the horizontal retrace period, the blanking pulse that is not subject to the inner band restriction of the signal can be suppressed at the rising and falling edges. It is possible to provide a television receiver that can reduce harmonics and is free from blanking interference caused by these harmonics.

In this embodiment, the frequency characteristics are switched using a resistor and a capacitor, but other means may be used.

Further, in this embodiment, it is most preferable to perform the switching immediately after the blanking circuit, but it may also be performed at a later stage. However, it is preferable before the signal is amplified to a large amplitude.

Effects of the Invention As described above, the present invention includes a control circuit that switches the frequency characteristics of the video signal amplification circuit to a wider band during horizontal scanning than during the horizontal retrace period. The frequency characteristics of the desired video signal amplification circuit can be freely selected without being restricted, and blanking interference caused by harmonics generated from the leading or trailing edge of the blanking pulse can be eliminated. Its practical effects are significant.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a video signal amplification circuit of a television receiver according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining its operation, and FIG. 3 is a block diagram of a conventional television receiver. , FIG. 4 is a circuit diagram of a video signal amplification circuit of a conventional television receiver. 1...Speed up capacitor, 2~4゜3
2-37 and 42-44...Resistance, 6,38-
41 and 48-51...transistor, 7.45
・・・・・・Capacitor, 6,46.47・・・・・・
Diode, 29...CRTo

Claims (1)

[Claims] A television comprising a video signal amplification circuit that drives a cathode ray tube, and a control circuit that switches the frequency characteristics of the video signal amplification circuit to have a wider band during a horizontal scanning period than during a horizontal retrace period. receiver.