JPH04311188A - Wide band cathode-ray tube driving circuit - Google Patents

Abstract

PURPOSE: To provide a wide band cathode-ray tube driving circuit which uses a differential amplifier to extend a high frequency response and a band width in a video signal processing system. CONSTITUTION: A video signal processing system, including a color difference signal generation means which generates color difference signals, a luminance signal generation means which generates a luminance signal, and a cathode-ray tube, is provided with a differential amplification means 41 which differentially amplifies the luminance signal and color difference signals to supply the cathode- ray tube and a current control means 42 which controls the current quantity on the current passage of the differential amplification means 41. Further, the system is provided with a buffer means 50, which is connected between the luminance signal generation means and the differential amplification means and buffers the luminance signal generated from the luminance signal generation means to supply it to the differential amplification means, or a reference level control means which automatically controls the reference level of the luminance signal generated by the luminance signal generation means in accordance with the brightness of a video signal sent on the transmission side. Thus, a picture having the high picture quality is vividly displayed.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode ray tube drive circuit in a video signal processing system, and more particularly to a wideband cathode ray tube drive circuit that widens the drive bandwidth of the cathode ray tube.

2. Description of the Related Art A typical example of a video display device is a cathode ray tube (CRT). Such a cathode ray tube drive circuit cannot improve the image quality displayed on the cathode ray tube unless it increases the frequency bandwidth and high frequency response of the video signal (or composite video signal) supplied to the cathode ray tube. . The degree of improvement in image quality is determined depending on the number of pixels in a line and the number of scanning lines. That is, the greater the number of pixels and the number of scans in a line, the higher the quality of the image that can be displayed on the cathode ray tube. Therefore, in a standard video signal processing system with 525 scanning lines, the frame scanning frequency (=30Hz) x
Number of scanning lines (=525) x number of dots (≒266) = 4.
2 (MHz), and the frequency drive band of the cathode ray tube is 4.2 MHz. Therefore, if this standard type cathode ray tube driving circuit has a frequency bandwidth of 4 to 5 MHz, it is possible to display a standard video signal on the cathode ray tube without deteriorating the image quality. A conventional cathode ray tube drive circuit uses a cascade amplifier, which is mainly used in high frequency circuits, as shown in FIG. The cascade type is configured such that a common emitter transistor Q2 and a common base transistor Q1 are connected in series. First, the color difference signal (RY) demodulated and output by the color difference signal processing section 10 is applied to the base of the common emitter transistor Q2 of the drive amplification section 40, and the brightness signal processing section 20 has already manually adjusted the brightness and A negative polarity luminance signal (-Y) with adjusted brightness is connected to the resistor R.
5 to the emitter of transistor Q2. Since the transistor Q2 is of the NPN type, it inverts and amplifies the color difference signal (RY) applied to its base input terminal. Therefore,
At point A on the collector side of transistor Q2 is {-(R-
Y)+(-Y)}=(-R) signal is high-frequency amplified and output. The output (-R) signal is applied to the emitter of the common base transistor Q1 and amplified and output to the collector side, and the amplified and output primary color signal R is applied to the cathode image intensity control electrode 31 of the cathode ray tube 30 through the current limiting resistor R2. applied. In the case of the cascaded amplifier described above, the temperature-dependent amplification (or DC current gain) hFE is adjusted for drift due to changes in the forward biased junction voltage VBE and the reverse saturation current ICBO. difficulties arise. Further, even if any one of the aforementioned amplification degree, forward biased junction voltage, and reverse saturation current changes, the output voltage will differ. Since this changed output voltage value cannot be distinguished from that caused by conversion of the input signal voltage, there is a problem that stability is reduced. However, the video frequency band that can be covered by a cathode ray tube drive circuit using a cascade amplifier is about 4 to 5 MHz, which is sufficient for use in general video signal processing systems.

[Problem to be solved by the invention] However, in recent years,
Devices have been developed that display high quality images by greatly increasing the number of scanning lines and pixels. for example,
HD (High Dehinition) TV, ID (
Improved Definition) TV,E
D (Enhanced Definition) TV
etc. A wideband cathode ray tube drive circuit having a frequency band of about 8 to 20 MHz is required as a cathode ray tube drive circuit used in these devices. Therefore, when the above-mentioned cascade type amplifier is used, there is a problem that an image of sufficiently high quality cannot be displayed. In order to solve these problems, an object of the present invention is to provide a wideband cathode ray tube driving circuit that uses a differential amplifier to increase high frequency response and bandwidth in a video signal processing system.

[Means for Solving the Problems] In order to achieve the above-mentioned object, a wideband cathode ray tube drive circuit of the present invention includes a color difference signal generating means for generating a color difference signal, a luminance signal generating means for generating a luminance signal, A video signal processing system including a cathode ray tube, a differential amplification means for differentially amplifying the luminance signal and the color difference signal and supplying the same to the cathode ray tube, and adjusting the amount of current on a current path of the differential amplification means. and current adjustment means. Furthermore, a buffering means is provided, which is connected between the luminance signal generation means and the differential amplification means, and buffers the luminance signal generated from the luminance signal generation means and supplies the buffered luminance signal to the differential amplification means. Furthermore, means is provided for automatically adjusting the reference level of the signal outputted by the buffering means according to the brightness of the video signal sent out from the transmitting side. Further, information corresponding to the brightness of the video signal is provided by a flyback transformer. Here, the current adjusting means adjusts the total amount of current of the differential amplifying means by varying the gain using a variable resistor. Furthermore, the apparatus further includes a reference level adjusting means for automatically adjusting the reference level of the luminance signal generated by the luminance signal generating means according to the brightness of the video signal sent out from the transmitting side.

[Operation] In the broadband cathode ray tube drive circuit of the present invention, the differential amplification means differentially amplifies the luminance signal and the color difference signal supplied to the cathode ray tube, and the current adjustment means controls the amount of current of the differential amplification means. As a result, the high frequency response to the applied video signal and the bandwidth of the amplifier can be increased to fully display a high quality screen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 is a diagram showing the configuration of the broadband cathode ray tube drive circuit of this embodiment. Here, the color difference signal processing section 10 and the luminance signal processing section 20 are configured similarly to known ones as in FIG. 1. The drive amplification section 40 includes a differential amplification section 41 composed of two transistors Q3 and Q4.
and a current adjusting section 42 composed of a common emitter transistor Q5 whose collector is connected to an emitter coupling point C where the transistors Q3 and Q4 are commonly coupled. In the differential amplification section 41, the base of the transistor Q3 is connected to the output terminal (R-Y) of the color difference signal processing section 10 through the resistor R10.
The collectors of transistor Q3 and transistor Q4 are connected to power supply B+ through collector resistors R7 and R8 and connection point D, respectively. An inductor L1 and a resistor R6 are connected in series between the node D and the power supply B+, and the node D is connected to the cathode end 31 of the cathode ray tube through a resistor R9. In the current adjustment section 42, a resistor R12 and a variable resistor R13 are connected in series between a power supply B+ and a ground potential GND, and a base of a transistor Q5 is connected to a connection point between the resistor R12 and the variable resistor R13. There is. The buffer section 50 is configured such that a grounded emitter transistor Q6 and a grounded collector transistor Q7 are connected in cascade between the luminance signal processing section 20 and the drive signal amplification section 40. Grounded emitter transistor Q
6 has bias resistors R15 and R16 connected to its base, a power supply B+ connected to its collector through a resistor R14, and a ground potential GND connected to its emitter through a resistor R17 and a capacitor C1 connected in parallel. Collector ground (or emitter follower)
r follower)) Transistor Q7 has its base connected to the collector of transistor Q6. A bias resistor R18 is connected between the connection point E between the base of the transistor Q7 and the collector output terminal of the transistor Q6 and the ground potential GND, the supply power B+ is connected to the collector of the transistor Q7, and the emitter of the transistor Q7 is connected to the ground potential GND. A resistor R19 is connected between the GND and the ground potential GND. The emitter of transistor Q7 is connected through resistor 11 to the base of transistor Q4 in differential amplifier section 41. The automatic brightness limiter 60 is connected between a flyback transformer and the buffer 50. That is, the automatic beam limiter (ABL) of the flyback transformer
am Limiter) is connected to the base of a common collector transistor Q8, and the emitter of the transistor Q8 is connected to the emitter of the transistor Q7. At this time, the emitter of transistor Q8 and transistor Q7
Voltage distribution resistors R20 and R21 and a diode D1 are connected between the emitter and the emitter. Voltage distribution resistors R22, R24, current limiting resistor R24, and AC bypass capacitor C2 are connected to the base of transistor Q8. In FIG. 2, the color difference signal processing section 10 and the luminance signal processing section 20 operate in the same manner as in FIG.
-Y) and a negative polarity luminance signal (-Y). The (RY) signal output from the color difference signal processing section 10 is input to the base of the transistor Q3 of the differential amplification section 41 through the resistor R10. On the other hand, the negative polarity luminance signal (-Y) of the luminance signal processing section 20 is applied to the base of the transistor Q4 of the differential amplifier section 41 through the buffer section 50 and the resistor R11. The negative luminance signal (-Y) applied to the buffer section 50 is applied to the base of the transistor Q6, is inverted and amplified, and appears in the form of an inverted luminance signal Y at the collector of the transistor Q6. At this time, the capacitor C1 has a peaking (pea
king) is used for compensation. This inverted and amplified luminance signal Y is applied to the base of transistor Q7. Transistor Q7 serves as a buffer to prevent the gain from decreasing due to load. That is, the buffer section 5
0 is a portion that performs impedance matching so that the applied luminance signal Y can be applied to the base of the transistor Q4 of the differential amplification section 41. On the other hand, the automatic brightness limiter 6
At 0, if the brightness of the video signal sent out from the transmitting side is bright from the ABL terminal of the flyback transformer (output transformer for the horizontal deflection coil), a low level voltage is applied.
If it is dark, a high level voltage is generated. The AC component of the signal generated from ABL of this flyback transformer is removed by capacitor C2 before being applied to the base of transistor Q8, and voltage distribution resistors R22 and R24
The pressure is divided by Transistor Q8 linearly amplifies the voltage supplied to its base depending on the voltage state applied to the ABL terminal of the flyback transformer, thereby changing the voltage appearing at its emitter. Further, the voltage at the emitter of transistor Q8 is divided by voltage distribution resistors R21 and R22, and then passed through one-way diode D1 to transistor Q.
The brightness of the video signal is adjusted by controlling the reference level of the luminance signal applied to the emitter of transistor Q7 and output from the emitter of transistor Q7. The brightness signal Y adjusted in this way is applied to the base of the transistor Q4 of the differential amplifier section 41. The differential amplification section 41 amplifies the difference {-(RY)-Y}=(-R) signal between the (RY) signal and the Y signal input to the bases of the transistors Q3 and Q4 on both sides. and output through connection point D. At this time, in order to change the gain, the transistor Q5
Transistors Q3 and Q4 according to the adjustment of variable resistor R13.
control the total amount of current. Then, the difference signal (-R) on the connection point D amplified by the transistor Q3 and the transistor Q4 peaks (p
The current is controlled by resistor R9 and applied to the cathode image intensity control electrode (not shown) of the cathode ray tube. At this time, the amplified difference signal (
-R) is applied in the state of the primary color signal R as shown in FIG. 1 through a buffer (for example, a configuration such as transistor Q1 in FIG. 1).

According to the present invention, it is possible to provide a wideband cathode ray tube drive circuit that uses a differential amplifier to increase high frequency response and bandwidth in a video signal processing system. That is, the present invention uses, in a cathode ray tube drive circuit of a video signal processing system, a differential amplifier that can amplify a DC component, has excellent bias stability, and operates stably even over a wide range of temperature and power fluctuations. This has the advantage of increasing the high frequency response to the video signal and the bandwidth of the amplifier, allowing the cathode ray tube to display a high-quality screen.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional broadband cathode ray tube drive circuit.

FIG. 2 is a diagram showing the configuration of a broadband cathode ray tube drive circuit of this embodiment.

[Explanation of symbols]

Claims (6)

[Claims] 1. A video signal processing system including a color difference signal generating means for generating a color difference signal, a luminance signal generating means for generating a luminance signal, and a cathode ray tube, wherein the luminance signal and the color difference signal are differentially amplified. 1. A wideband cathode ray tube drive circuit, comprising: differential amplification means for supplying a current to the cathode ray tube; and current adjustment means for adjusting the amount of current on a current path of the differential amplification means. 2. A buffering means connected between the luminance signal generation means and the differential amplification means, buffering the luminance signal generated from the luminance signal generation means and supplying the buffer to the differential amplification means. The broadband cathode ray tube drive circuit according to claim 1, further comprising: a wideband cathode ray tube drive circuit; 3. The broadband cathode ray tube according to claim 2, further comprising means for automatically adjusting the reference level of the signal outputted by the buffering means according to the brightness of the video signal sent out on the transmitting side. drive circuit. 4. The broadband cathode ray tube drive circuit according to claim 3, wherein information corresponding to the brightness of the video signal is provided by a flyback transformer. 5. The broadband cathode ray tube drive circuit according to claim 1, wherein the current adjusting means adjusts the total amount of current of the differential amplifying means by varying the gain using a variable resistor. 6. The apparatus further comprises a reference level adjusting means for automatically adjusting the reference level of the luminance signal generated by the luminance signal generating means according to the brightness of the video signal sent out on the transmitting side. 2. The broadband cathode ray tube drive circuit according to item 1.