KR920008110Y1 - Video pre-amp circuit - Google Patents

Abstract

No content.

Description

Video preamplifier circuit

1 is a conventional video preamplifier circuit diagram.

2 is a waveform diagram of a main portion of a conventional video preamplifier.

3 is a circuit diagram of a video preamplifier according to the present invention.

4 is a waveform diagram of the main part of the video preamplifier circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

10: DC regeneration unit 20: differential amplifier

30: contrast control part 40: DC clamping part

50: cathode ray tube drive unit 60: differential amplification control unit

Q1 to Ql0: Transistors R1 to R23: Resistance

VR1: Variable resistor ZD1 ~ ZD3: Zener diode

C1: Capacitor D1: Diode

The present invention relates to a monitor, and more particularly, to a video preamplifier circuit that simply constitutes a clamping circuit for controlling the back raster of a monitor not to be changed during a blanking time of an input video signal.

The conventional video preamplifier circuit is configured as shown in FIG. 1, and the waveform diagram of the main part is shown in FIG.

At this time, the video signal VS input as shown in FIG. 2 is applied to the contact point a after the direct current component is blocked by the capacitor C1.

At this time, when the video signal is not applied to the voltage of the contact (a) Therefore, when the video signal VS of about 0.7V is applied, the video signal VA, which always maintains the constant voltage V1 or more, is formed at the contact point a as shown in FIG.

Therefore, the differential amplifier 20 which differentially amplifies the video signal VA of the contact point a amplifies the entire video signal display function period T2 and the blanking time Tl of the video signal VA, thereby controlling the rear contrast controller. Is applied to (30).

At this time, since the collector current I3 of the transistor Q2 of the differential amplifier 20 is constant, the transistor (B) is adjusted by adjusting the variable resistor VRl of the contrast controller 30 to adjust the potential of the contact point b. The current I1 flowing in Q5 and the current I2 flowing in the transistor Q4 increase.

In addition, when the current I1 flowing in the transistor Q5 decreases, the voltage drop caused by the resistor R11 also decreases, so that the potential of the blanking time T1 of the video signal VB formed at the contact point c becomes second. As shown in the figure, it descends by ΔV.

Contrary to the above, when the potential of the contact C is increased by the variable resistor VR1, the current I1 increases and the voltage caused by the resistor R11 increases, thereby causing the video signal VB during the blanking time T1. The potential of the formed contact C is increased by ΔV as shown in FIG.

At this time, the potential formed at the contact point C is changed by the variable resistor VR1 of the contrast controller 30 so that the video signal VB as shown in FIG. 2 VB is the transistor Q6 of the contrast controller 30. When it is applied to the cathode ray tube drive unit 50 through the emitter side of), during the video signal display function period T2 of the video signal VB, the cathode ray tube drive unit 50 is normally driven to reduce contrast on the cathode ray tube. Although it can be controlled, the potential of the blanking time T1 is changed by the variable resistor VR1 in the differential amplifier 20 during the blanking time T1, so that the brightness of the raster of the screen is changed.

That is, by adjusting the output voltage (contact point c) of the differential amplifier 20 by adjusting the variable resistor VR1, the contrast for controlling only the brightness of the image signal displayed on the screen can be controlled. The potential during the time T1 is variable, which causes a problem that the raster of the screen is changed.

This problem is conventionally solved by constructing a DC clamping part 40 between the differential amplifier 20 and the cathode ray tube drive part 50.

That is, a high level blanking signal VP or a synchronization signal is input to the DC clamping unit 40 during the blanking time T1 of the video signal VS applied to the DC reproducing unit 10.

Accordingly, the transistor Q9 is driven by the blanking signal VP during the blanking time T1 of the video signal VS, thereby turning on the transistor Q7.

At this time, the inverted video signal VB of the video signal VS is applied to the contact point d through the transistor Q6, but the transistor Q7 is turned on during the blanking time T1, and the contact point ( In d), the voltage V3 of the saturated voltage VCE of the transistor Q7 and the driving voltages of the diode D1 and the control diode ZD3 is equal to that of the video signal VC of FIG. Is formed.

Therefore, even when the potential of the video signal VB output from the differential amplifier 20 is changed during the blanking time T1, the cathode ray tube drive unit may be driven by the blanking signal VP of the DC clamping unit 40. Since the potential during the blanking time T1 applied to 50) is kept constant, the back raster is kept constant even when the contrast is controlled by adjusting the variable resistor VR1.

However, such a conventional video preamplifier circuit requires a separate blanking signal or a synchronization signal in order to keep the back raster constant, and there is a problem in that the DC clamping circuit is complicated in structure and cannot be miniaturized and lightweight.

This invention solves this problem, and the object of this invention is to stop the driving of the differential amplifier during the blanking time of the video signal, so that the DC regeneration unit and the DC clamping unit are not necessary, so that the video preamp can be simplified. To provide a circuit.

The present invention is characterized by a differential amplifier for amplifying an input video signal, a contrast controller connected to the differential amplifier to control the contrast by controlling the amplification ratio of the differential amplifier, A video preamplifier circuit comprising a cathode ray tube drive unit connected to a contrast control unit for driving a cathode ray tube by inputting a video signal amplified by the contrast control unit, the base side of which is grounded, a constant voltage terminal connected to the collector side, and the differential on the emitter side And a differential amplifying control unit comprising a transistor which is connected to the amplifying unit and the negative voltage terminal in parallel and is always turned on. Featured video program It is in the reamplifier circuit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a video preamplifier circuit diagram according to the present invention, and includes a differential amplifier 20, a contrast controller 30, a cathode ray tube drive unit 50, and a differential amplifier 60.

More specifically, the differential amplifier 20 for amplifying the input video signal VS causes the video signal VS to be applied to the base side of the amplifying transistor Q2, and the transistor Q2. Is a differential amplifier formed by connecting the amplifying transistors Q4 and Q5 to the collector side.

The differential amplifier 60 stops driving of the differential amplifier 20 during the blanking time T1 of the video signal VS. The video signal VS is biased through the resistor R1. The emitter side of the transistor Q2 configured in the differential amplifier 20 is connected to the base side of the transistor Q10 and to the emitter side of the transistor Q10.

In this case, since the other end of the resistor R1 connected to the base side of the transistor Q10 is grounded, the video signal VS is not applied to the base side of the transistor Q10 and flows to the ground end as it is. The base side of Q10) is grounded.

In addition, the negative voltage (-VBB) is applied to the emitter side of the transistors Q10 and Q2 so that the transistor Q10 is always turned on.

The contrast controller 30, which is connected to the differential amplifier 20 and adjusts the contrast of the screen by controlling the amplification ratio of the differential amplifier 20, the transistor Q5 of the differential amplifier 20. Contrast adjustment variable resistor VR1 is connected to the base side of the resistor R13, and the base side of the amplifying transistor Q6 is connected to the collector side of the transistor Q5 of the differential amplifier 20, As the variable resistor VR1 is adjusted, the potential applied to the base side of the transistor Q6 is different.

The cathode ray tube drive unit 50 for driving the cathode ray tube (CRT) by inputting the video signal amplified by the contrast control unit 30 is disposed on the emitter side of the transistor Q6 configured in the contrast control unit 30. It is connected in parallel with the resistor R22.

4 is a waveform diagram of a main part of a video preamplifier circuit according to the present invention, and (VS) is a waveform diagram of a video signal VS applied to the differential amplifier 20 and the differential amplification controller 60 of FIG. (VD) is a waveform diagram of a video signal appearing at the contact point e when a video signal VS of 0.7V is supplied in FIG. 3, and (VB) is a blanking time T1 of the video signal VS. And waveforms of the video signal appearing at the contact point c in FIG. 3 during the video signal display possible period T2.

In this configuration, since the base side of the transistor Q10 of the differential amplification controller 60 is grounded and the negative voltage -VBB is applied to the emitter side, it is always turned on regardless of the input video signal VS. The potential of the contact f is always kept at -0.7V.

At this time, when the 0.7 V video signal VS is applied to the base side of the transistor Q2 of the differential amplifier 20 as shown in FIG. 4, the video signal VS during the video signal displayable period T2 is Since the amplification is performed on the transistor Q2 of the differential amplifier 20, the waveform of the emitter side of the transistor Q2, that is, the contact point e is as shown in FIG. 4. The current 13 flowing to the collector side of the transistor Q2 is determined by the potential difference between the contacts e and f regardless of the base potentials of the transistors Q4 and Q5.

The current I6 flowing to the emitter side of the transistor Q2 is almost the same as the current I3 flowing to the collection side of the transistor Q2, so the amount of current is the contact at the potential value of the contact e. It is almost the same as subtracting the potential value of (f) divided by the resistance value of the resistor (R8).

If you express it as a formula,

At this time, the current I3 flowing to the collector side of the transistor Q2 is equal to the sum of the currents I4 and I5 flowing to the emitter side of the transistors Q4 and Q5 (I3 = I4 + I5). ) And the current I4 flowing to the emitter side of the transistors Q4 and Q5 by adjusting the potential applied to the base side of the transistors Q4 and Q5 with the variable resistor VR1 of the contrast control unit 30. ) And (I5) are varied so that a constant constant current I3 always flows to the collector side of the transistor Q2.

At this time. When the variable resistance VR1 of the contrast control unit 30 is controlled to lower the base-side potential of the transistor Q5, the current I1 applied to the transistor Q5 is reduced to display the image signal display period ( During T2, the potential formed at the contact c increases, and when the base side potential of the transistor Q5 is increased, the potential formed at the contact c during the video signal display possible period T2 decreases.

That is, during the video signal display possible period T2, the potential formed at the contact point c is changed in accordance with the adjustment of the variable resistor VR1 of the contrast control unit 30, such as the voltage V1 shown in FIG. It is applied to the tube drive unit 50, thus changing the contrast of the image displayed on the cathode ray tube (CRT).

However, when the video signal VS reaches the blanking time T1, since the contacts e and f are all close to -0.7 V, the current I6 flowing through the resistor R8 is almost OA. Becomes

At this time. Since the current I3 flowing on the collector side of the transistor Q2 is almost the same as the current I6 flowing on the emitter side, the current I3 flowing on the collector side is also almost OA.

The current (I3) flowing in the collector side of the transistor (Q2) is the sum of the currents (I4) and (I5) flowing in the emitter side of the transistors (Q4) and (Q5). (I5) is also almost OA.

Substituting this into equation (1),

At this time, since 14 + 15 = 0, 14 + 15 = 0.

Therefore, the potential formed at the contact point c during the blanking time T1 of the video signal becomes the voltage VBB since there is almost no voltage drop across the resistor R11 due to the driving of the transistor Q5.

Therefore, during the blanking time T1, the potential of the contact point c is always constant VBB regardless of the adjustment of the variable resistor VR1 of the contrast control unit 30, so that the constant potential is also supplied to the cathode ray tube drive unit 50. As a result, the backlast of the cathode ray tube CRT becomes constant.

As described above, during the display signal period T2 of the video signal VB output from the differential amplifier 20, the potential is controlled by the variable resistor VR1 of the contrast control unit 30, so that the cathode ray tube drive ( 50, but the output potential (contact point (c)) of the differential amplifier 20 is set to a constant voltage (VBB) by the differential amplifier 60 during the blanking time (T1) of the video signal (VB). Is maintained and applied to the cathode ray tube drive unit 50.

Accordingly, the cathode ray tube drive unit 50 displays an image displayed on the cathode ray tube CRT by a potential which is changed under the control of the variable resistor VR1 of the contrast control unit 30 during the image signal display possible period T2. Although the contrast of is changed, a constant potential VBB is applied to the contrast control unit 30 during the blanking time T1 to maintain the back raster of the cathode ray tube CRT constant.

In other words, the present invention eliminates the need for the conventional DC regeneration unit and the DC clamping circuit by stopping the driving of the differential amplification unit and keeping the output potential constant during the blanking time of the video signal applied to the differential amplifier. By simplifying the configuration, it is possible to reduce the size and weight.

Claims (1)

A differential amplifier 20 for amplifying the input video signal VS and a contrast controller 30 connected to the differential amplifier 20 to control the contrast by controlling the amplification ratio of the differential amplifier 20. And a cathode ray tube drive (50) connected to the contrast control unit (30) to drive a cathode ray tube (CRT) by inputting a video signal amplified by the contrast control unit (30). The side is grounded and a constant voltage terminal (VBB) is connected to the collector side, and the differential amplifier 20 and the negative voltage terminal (-VBB) are connected in parallel to the emitter side and are always turned on so that the potential of the contact point f is negative. And a differential amplification control unit 60 made of transistor Q10 held at 0.7 V), and maintains the output potential of the differential amplifier 20 at a constant voltage VBB during the blanking time T1. Backlaster schedule Video preamplifier circuit, comprising a step of maintaining it.