JPH0546104A - Video signal amplifying circuit - Google Patents

Abstract

PURPOSE:To obtain a video signal amplifying circuit for video display which can obtain constant brightness regardless of the number of scanning lines in a multiscan system CRT display device. CONSTITUTION:A video amplifier IC 2 is composed of an IC and a scanning line quantity detecting circuit 21 is provided in the IC and a circuit which generates a voltage in inverse proportion to the number of scanning lines according to the horizontal synchronizing signal 10 and vertical synchronizing signal of a video signal 1 applied to a CRT display device is provided and the amplification degree of a video output amplifier 3 is varied with this voltage to obtain a voltage value which is in inverse proportion to the number of scanning lines of the driving voltage of a CRT 4, thereby eliminating a brightness difference due to a difference in the number of scanning lines.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the number of scanning lines and reduces the brightness per unit area of the display screen when a signal with a small number of scanning lines is used. The present invention relates to a video signal amplifier circuit having a function of keeping the luminance constant regardless of the number of scanning lines by increasing the output of the amplifier by changing it so as to be proportional.

[0002]

2. Description of the Related Art In recent years, cathode ray tube display devices (hereinafter referred to as CRT displays) have many products (hereinafter referred to as multi-scan monitors) that are capable of displaying various types of screens on a single monitor, and are on the market. Has been put into. There are many different kinds of frequencies and scanning lines of the display signals applied to such a multi-scan monitor, but a video amplifier for amplifying these display signals is designed to support one mode. It does not change according to many kinds of signals.

A conventional multi-scan monitor will be described below.

FIG. 4 shows a configuration example of a conventional multi-scan monitor. In FIG. 4, 1 is a video signal, 2 is a video preamplifier, 3 is a video output amplifier, 4 is a cathode ray tube.
(CRT) 5 is a sync separation circuit, 6 is a horizontal deflection circuit, 7 is a vertical deflection circuit, 8 is a mode switching circuit, and 9 is a contrast adjustment VR.

The operation of the video amplifier of the multi-scan monitor configured as above will be described below. First, the video signal 1 applied to the video preamplifier 2 is amplified up to several V and the contrast adjustment VR is applied.
After being amplified to several tens of volts by the video output amplifier 3 through 9, it is applied to the CRT 4 (cathode) and displayed on the screen.

On the other hand, the video signal 1 is the video preamplifier 2
After being amplified by, the sync separation circuit 5 outputs two horizontal and vertical sync signals 10 and 11. These two synchronization signals 10 and 11 are applied to the horizontal deflection circuit 6, the vertical deflection circuit 7 and the mode switching circuit 8, respectively.

The mode switching circuit 8 generates a voltage, a switch signal, etc. adapted to the deflection frequency of the input video signal 1 and supplies it to both the horizontal and vertical deflection circuits 6 and 7.

As a result, the deflection matching the input video signal 1 is performed.

[0009]

As is well known, CRTs are well known.
Is displayed by the electron beam hitting the phosphor coated on the tube surface, and at this time, the phosphor at the irradiated position emits light. At this time, the amount of emitted light is proportional to the speed and amount of the irradiated electron beam. That is, the amount of light emission also increases in proportion to the voltage driving the CRT.

On the other hand, the brightness perceived by humans is proportional to the number of phosphors emitting light per unit area. Therefore, in a CRT driven by the same voltage, the luminance per unit area increases in proportion to the number of scanning lines.

In the above-described multi-scan monitor, when signals with significantly different numbers of scanning lines are added, the brightness of the two signals also greatly differs.

In order to prevent the difference in brightness from occurring, for a video signal having a large number of scanning lines, the size of the signal applied to the video amplifier is changed stepwise according to the number of scanning lines. In a video amplifier capable of changing the amplification degree in a direct current (hereinafter referred to as DC contrast), the voltage of DC contrast is changed between two signals to cope with the problem.

However, since the frequency of the video signal 1 handled by the CRT display monitor is as high as tens to hundreds of tens of MHz, the direct switching circuit in the transmission path of the video signal increases lead inductance and straight capacitance. Therefore, the frequency characteristic is deteriorated and it is impossible.

In addition, it is difficult to stably amplify the noise because unnecessary oscillations occur.

Moreover, the color CRT is, as is well known, a red,
It is composed of three electron guns of green and blue, and various colors are displayed by a combination of three primary colors of phosphors emitted by these three electron guns.

That is, various colors are displayed by keeping the ratio of the amplitude values of the video signal voltages for driving the red, green, and blue electron guns of the color CRT constant (hereinafter referred to as white balance).

In such a color CRT display monitor, it is necessary to correct the change in brightness caused when the number of scanning lines is significantly different while maintaining the white balance, which requires a lot of white balance adjustment man-hours. is there.

The present invention solves the above-mentioned conventional problems. Even in a multi-scan monitor having a significantly different number of scanning lines, there is no difference in brightness, and there is no increase in white balance adjustment man-hours. The purpose is to improve.

[0019]

According to the present invention, a video preamplifier for amplifying a video signal is integrated into an IC and a scanning line number detection circuit is provided in the IC, and the amplification degree is changed in inverse proportion to the number of scanning lines. It is characterized in that the output voltage of the video amplifier is changed.

[0020]

According to the present invention, even when the number of scanning lines changes significantly, the output amplitude of the video amplifier, that is, the drive voltage of the CRT can be changed to make the brightness of the display screen constant. Further, since the video preamplifier is integrated into an IC, the lead inductance and the straight capacitance do not increase, the frequency characteristic is not deteriorated, and the oscillation does not occur.

Moreover, the white balance is not disturbed and the productivity is not deteriorated.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit configuration diagram according to an embodiment of the present invention, in which a portion surrounded by a chain line is an integrated video preamplifier, and a video signal 1 is supplied at a constant level (several V).
Depending on the number of scanning lines of the video preamplifier 20 that amplifies the signal, the horizontal and vertical sync signals 10 and 11 of the sync separation circuit 5 and detects the number of scanning lines, and the number of scanning lines of the scanning line number detection circuit 21. The gain control circuit 22 controls the output of the video preamplifier 20. Other numerical symbols that are the same as those in FIG. 4 indicate the same parts or circuits.

FIG. 2 shows the video preamplifier IC 2 shown in FIG.
2 is a block diagram showing the internal configuration of the scanning line number detection circuit 21 surrounded by the alternate long and short dash line, which is a monostable multivibrator 21-that receives the horizontal synchronization signal 10 from the synchronization separation circuit 5 as an input.
1, a gate circuit 21-2 which also receives the vertical sync signal 11 from the sync separation circuit 5, and a monostable multivibrator 21
A circuit 21-3 that integrates the output of -1 and a peak hold circuit 21-4 that extracts the peak value P ₁ of the integration circuit and outputs the corresponding DC value P ₂ to the gain control circuit 22.
Incidentally, C ₁ and C ₂ are the integrating capacitors and the holding capacitors of the integrating circuit 21-3 and the peak hold circuit 21-4, respectively.

FIG. 3 shows the voltage waveform of each part of FIG. 2, and the operation of the video preamplifier IC will be described below with reference to this voltage waveform.

First, the horizontal sync signal 10 ((a) in FIG. 3) which is sync-separated from the video signal 1 by the sync separator 5 is applied to the monostable multivibrator 21-1 of the scanning line number detector 21, A pulse train having a constant pulse width that matches the cycle of the horizontal synchronizing signal and is independent of the pulse width of the horizontal synchronizing signal is generated.

When this pulse train is applied to the integrating circuit 21-3 and integrated, an output that increases with time is obtained.

On the other hand, the vertical sync signal 11 ((a) in FIG. 3) which has been sync-separated by the sync separation circuit 5 is applied to the gate circuit 21-2 of the scanning line number detection circuit 21, and the output thereof is the integrating capacitor C.
Connected to ₁ .

The gate circuit 21-2 is connected so as to discharge the integrating capacitor C ₁ when the vertical synchronizing signal 11 arrives. As a result, the integration circuit 21
The output of -3 becomes a sawtooth wave as shown in FIG. When the peak value P ₁ of the sawtooth wave is extracted by the peak hold circuit 21-4, the DC value P ₂ shown in FIG. 3D can be obtained.

At this time, the peak value of the sawtooth wave is the horizontal synchronization signal.
It is proportional to the frequency of 10 and inversely proportional to the frequency of the vertical synchronizing signal 11.

On the other hand, the number of scanning lines is also proportional to the frequency of the horizontal synchronizing signal 10 and inversely proportional to the frequency of the vertical synchronizing signal 11.

This indicates that the output of the peak hold circuit 21-4 changes in proportion to the number of scanning lines.
Therefore, if the output voltage of the peak hold circuit 21-4 is output to the gain control circuit 22 to control the amplification degree of the video output amplifier 3, a video signal according to the number of scanning lines can be obtained.

The CRT 4 is driven by this video signal output.

[0033]

As described above, in the video signal amplifying circuit of the present invention, the video preamplifier portion is integrated into an IC and a detection circuit for the number of scanning lines is provided therein, and a CRT is provided with a video output inversely proportional to the number of scanning lines. By driving, the brightness of the display screen can be kept constant even in the case of signals in which the number of scanning lines is significantly different.

Further, since the number of scanning lines is automatically detected, there is an advantage that the white balance is not lost and the adjustment man-hour is not increased even if the number of scanning lines is largely changed.

In addition, since it is independent of the video signal path and integrated into an IC, lead inductance and straight capacitance do not increase, oscillation does not occur, and frequency characteristics are not affected, and stable amplification is possible. There is.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram according to an embodiment of the present invention.

2 is a block diagram showing an internal configuration of the video preamplifier IC of FIG. 1. FIG.

FIG. 3 is a diagram showing voltage waveforms of respective parts of FIG.

FIG. 4 is a diagram showing a configuration example of a conventional multi-scan CRT display monitor.

[Explanation of symbols]

1 ... Video signal, 2 ... Video preamplifier IC, 3 ...
Video output amplifier, 4 ... CRT, 5 ... Synchronous separation circuit, 6 ... Horizontal deflection circuit, 7 ... Vertical deflection circuit, 8 ... Mode switching circuit, 9 ... Contrast adjustment VR, 20 ... Video preamplifier, 21 ... Scan line number detection circuit , 21-1… Monostable multivibrator, 21-2… Gate circuit, 21-3
… Integrator circuit, 21-4… Peak hold circuit, 22… Gain control circuit.

Claims (1)

[Claims] 1. The number of scanning lines of an applied signal is detected, the amplification degree of an amplifier is changed in inverse proportion to the number of scanning lines, and a constant brightness is automatically obtained regardless of the number of scanning lines. A video signal amplifier circuit characterized in that it is obtained.