JPH08256024A - Amplifier circuit, cathode ray tube driving device and display device - Google Patents

Abstract

PURPOSE: To make a band wide at low cost while suppressing the influence of feedback capacitance. CONSTITUTION: A signal inputted from a signal input terminal 31 is amplified by an NPN transistor 32 and an NPN transistor 37 connected in cascade to the NPN transistor 32, and supplied to the base of an NPN transistor 81. The inputted signal is amplified by the NPN transistor 81 and supplied from its emitter to a cathode 41. When the frequency of the signal is low, the impedance of a capacitor 90 is reduced, and the high frequency component of the signal is impressed from the collector of the NPN transistor 81 through a resistor 89 and the capacitor 90 to the base of an NPN transistor 83. Thus, the NPN transistor 83 generates the component to be changed corresponding to the high frequency component in constant current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit, a cathode ray tube driving device and a display device, and particularly to an amplifier circuit and a cathode ray tube driving device suitable for driving a cathode ray tube for displaying an image output from a computer. And a display device.

[0002]

2. Description of the Related Art A cathode ray tube driving device is a circuit for amplifying a video signal and supplying it to a cathode of a cathode ray tube or a first grid, and has a band of several tens Hz to several tens MHz, and in some cases up to 200 MHz. Wide bandwidth of 30
A wide voltage amplitude characteristic of V to 100 V is required.

As an amplifier circuit satisfying these conditions,
The circuit shown in FIG. 5 is known. In this example, N
An NPN transistor 37 is cascode-connected to the collector of the PN transistor 32. The emitter of the NPN transistor 32 is grounded by the resistor 33, and also grounded by the resistor 34 and the capacitor 35. The collector of the NPN transistor 37 has a resistor 3
8 is connected to a predetermined voltage source (75V).
The base of the NPN transistor 32 has a signal input terminal 3
The video signal is input from 1 and the NPN transistor 37
A constant voltage (12 V) is supplied from the terminal 36 to the base.

The collector of the NPN transistor 37 is connected to the cathode 41 of the cathode ray tube via the coupling capacitor 39 and the resistor 40. A discharge gap 42 is provided at a connection point between the cathode 41 and the resistor 40 of the cathode ray tube. A clamp diode 43 and an adjustable voltage source 44 that regulates the clamp voltage are connected to the connection point between the resistor 40 and the capacitor 39.

Further, the collector of the NPN transistor 37 has a discharge gap 4 in addition to the capacitance of the cathode 41 itself.
2, stray capacitances such as a clamp diode 43, a protection diode, a cathode ray tube socket, and other patterns (not shown) are connected as a load capacitance 45. The value CL of this load capacitance often reaches a dozen PFs.

In this example, the video signal input from the signal input terminal 31 is the NPN transistors 32 and 3.
Amplified by a cascode amplifier composed of 7,
It is supplied to the cathode (R cathode) 41 of the cathode ray tube through the capacitor 39 and the resistor 40.

When this circuit is used for R color signals, the other G and B color signals are also supplied to the corresponding cathodes by the same amplifier circuit.

Further, since the value of the load capacitance 45 is large, as shown in FIG. 6, especially when the video signal is drastically changed from a low level to a high level, the waveform thereof is blunted (the rising characteristic is deteriorated). There were challenges.

The amplifier circuit of FIG. 5 has a value CL of the load capacitance 45.
Therefore, when the frequency of the video signal output from the collector of the NPN transistor 37 increases, the impedance of the load capacitance 45 decreases and it becomes difficult to supply the video signal to the cathode 41. That is, it becomes difficult to make the band wider (particularly, make the high frequency band wider). Therefore, in a high-definition display device that requires a wide band, there is a display device that satisfies the request by reducing the resistance value RL of the resistor 38 as a load resistance. Becomes large and heat generation becomes remarkable.

Therefore, for example, as shown in FIG.
A structure in which a buffer is added after the transistor 37 is also proposed. In this example, the base of the PNP transistor 63 is connected to the collector of the NPN transistor 37, and the collector of the PNP transistor 63 is grounded. The emitter of the PNP transistor 63 is connected to the NPN transistor 62 via the resistors 65 and 64.
Connected to the emitter. NPN transistor 62
Is connected to the voltage source 75V, and the base is connected to one end of the resistor 38.

One end of the resistor 38 and the NPN transistor 3
Two diodes 61 are connected to the collector of 7. That is, the NPN transistor 62 and the PNP transistor 63 form a complementary push-pull circuit. The connection point of the resistors 64 and 65 is connected to the cathode 41 via the capacitor 39 and the resistor 40. Other configurations are similar to those in FIG.

In this amplifier circuit, the signal output from the collector of the NPN transistor 37 is amplified and output by the push-pull connected NPN transistor 62 and PNP transistor 63. As a result, the charging / discharging operation for the load capacitance 45 is speeded up, and the band can be widened.

This amplifier circuit, as shown in FIG.
Both the time tf at which the video signal sharply falls and the time tr at which the video signal sharply rises are good values close to the ideal waveform shown by the solid line. A high-resolution monitor of 17 inches or more for a computer uses a hybrid I-type amplifier circuit as shown in FIG.
It is converted to C and used.

[0014]

As described above, in the example of FIG. 7, the load capacitance 45 is formed by the push-pull connection of the NPN transistor 62 and the PNP transistor 63.
The charging and discharging operations faster for, although're working to broadband, in parallel with the load resistor 38, not only the feedback capacitor C _re of the NPN transistor 62, a feedback capacitor C _re of the PNP transistor 63 is also connected. As a result, due to this feedback capacitance, there is a problem that there is a limit to widening the band.

Further, since the amplifier circuit shown in FIG. 7 constitutes a complementary push-pull circuit, it is PNP.
The transistor 63 is required. However, PNP
Generally, it is technically and economically difficult to manufacture a transistor having a high breakdown voltage and good high frequency characteristics. Therefore, the PNP transistor is a hybrid IC.
It is designed to be installed as a single transistor in.
Therefore, there is a problem that the cost is high.

If a monolithic IC is used,
Although it is possible to reduce the cost, it is necessary to replace all the transistors with NPN transistors.

The present invention has been made in view of such a situation, and is to make it possible to achieve a wider band at a lower cost.

[0018]

An amplifier circuit according to the present invention is provided with a first active element to which a signal input from a signal input terminal is supplied and a cascode connection to the first active element, and an input from a signal input terminal. A second active element that amplifies and outputs the generated signal, a third active element that amplifies and outputs the signal output from the second active element, and a signal input that is connected to the third active element A fourth active element that operates as a constant current source that generates a constant current including a component that changes corresponding to a high frequency component of the signal input from the terminal.

The first to fourth active elements can be of the same junction type, eg all NPN transistors.

The fourth active element is supplied with the high frequency component of the signal input from the third active element through the signal input terminal, or is supplied with the high frequency component of the signal input therein through the signal input terminal. be able to.

The cathode ray tube driving device of the present invention is a cathode ray tube driving device which amplifies a video signal and supplies it to the cathode or the first grid of the cathode ray tube. The first video signal supplied from the signal input terminal is supplied to the cathode ray tube driving device. Second active element that is cascode-connected to the first active element and that amplifies and outputs the video signal input from the signal input terminal, and the video signal output from the second active element A constant current source connected to the third active element and outputting a constant current including a component that changes corresponding to the high frequency component of the video signal input from the signal input terminal And a fourth active element that operates.

The display device of the present invention comprises a cathode ray tube for displaying an image and an amplifier circuit for amplifying a video signal and supplying the amplified video signal to the cathode or the first grid of the cathode ray tube. A first active element to which the video signal input from the terminal is supplied; and a second active element that is cascode-connected to the first active element and that amplifies and outputs the video signal input from the signal input terminal, Second
Third active element that amplifies and outputs the video signal output from the active element of, and a component that is connected to the third active element and that changes corresponding to the high frequency component of the video signal input from the signal input terminal And a fourth active element that operates as a constant current source that generates a constant current including.

[0023]

In the amplifier circuit according to claim 1, the cathode ray tube drive device according to claim 6 and the display device according to claim 7, cascode-connected first active elements and second active elements are provided. The signal amplified by is further amplified by the third active element and output. The constant current of the fourth active element connected to the third active element is controlled so as to change corresponding to the high frequency component of the signal. Therefore, it is possible to realize a device having excellent rising characteristics, falling characteristics, and high frequency characteristics.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration example of a monitor device to which an amplifier circuit of the present invention is applied. In this embodiment, the computer 1 outputs the generated R, G, B color signals to the D / A converters 1R, 1G, 1B of the computer 1, respectively.
To the amplitude adjustment circuits (preamplifiers) 11R, 11G, and 11B after D / A conversion. The amplitude adjusting circuits 11R, 11G and 11B adjust the mutual balance of the input R, G and B signals,
The brightness is adjusted and output. Amplitude adjusting circuits 11R, 11
The R, G, B signals output from G, 11B are amplified by the amplifier circuits 12R, 12G, 12B and supplied to the cathodes 13R, 13G, 13B of the cathode ray tube 13. The computer 1 can operate the keyboard 2 to input a predetermined command. Further, the computer 1 is adapted to appropriately record predetermined data and the like on the hard disk 3 and read it.

FIG. 2 shows an example of the structure of the amplifier circuit 12R (the amplifier circuits 12G and 12B have the same structure), and the portions corresponding to those in FIGS. 5 and 7 are designated by the same reference numerals. I am doing it.

In this embodiment, the base of an NPN transistor 81 serving as an emitter follower is connected to the collectors of the NPN transistor 32 and the NPN transistor 37 cascode-connected thereto.
The collector of the NPN transistor 81 is connected to the voltage source 75V via the resistor 82, and the emitter thereof is connected to the collector of the NPN transistor 83 that operates as a constant current source. At the base of the NPN transistor 83,
The constant voltage (12V) supplied from the terminal 36 is applied to the resistor 87.
The voltage is divided by 88 and 88, and the voltage is applied. The emitter is grounded by the resistor 84, and the resistor 85 and the capacitor 86 are also connected.
It is also grounded by the series circuit.

The base of the NPN transistor 83 is
It is connected to the collector of the NPN transistor 81 via a resistor 89 and a capacitor 90.

That is, in this embodiment, the complementary push-pull NPN transistor 62 and PNP transistor 63 in FIG. 7, and therefore the diode 61 and the resistors 64 and 65 attached thereto are omitted. Instead, the NPN transistor 81 and the NPN transistor 8 as its load are used.
3 is connected. Other configurations are
This is similar to the case in FIG.

Next, the operation will be described. The R, G, B color signals output from the computer 1 are D / A
After being D / A converted by the converters 1R, 1G and 1B, the amplitude is adjusted by the amplitude adjusting circuits 11R, 11G and 11B. The amplitude-adjusted R, G, B signals are
It is amplified by the amplifier circuits 12R, 12G, 12B and supplied to the cathodes 13R, 13G, 13B of the cathode ray tube 13. As a result, the image output from the computer 1 is displayed on the cathode ray tube 13.

In the amplifier circuit 12R, the signal output from the D / A converter 1R is input from the signal input terminal 31 to NP.
It is supplied to the base of the N-transistor 32. Therefore, this video signal is amplified by the NPN transistor 32 and the NPN transistor 37 that is cascode-connected to the NPN transistor 32 and constitutes a cascode amplifier.
It is supplied from the collector of the PN transistor 37 to the base of the NPN transistor 81. The NPN transistor 81 as an emitter foremplifies this signal and supplies it to the cathode 41 (corresponding to the cathode 13R in FIG. 1) of the cathode ray tube 13 via the capacitor 39 and the resistor 40. The presence of the NPN transistor 81 mainly improves the rising characteristics of the output video signal.

The signal output from the collector of the NPN transistor 81 passes through the resistor 89 and the capacitor 90,
Although supplied to the base of the NPN transistor 83, when the frequency of this signal is relatively low, the impedance of the capacitor 90 becomes large, and this signal component is not substantially supplied to the base of the NPN transistor 83. As a result, the base voltage of the NPN transistor 83 is
The voltage of 12 V applied from 6 is divided by resistors 87 and 88 to become a constant voltage, and the NPN transistor 83 operates as a constant current source.

On the other hand, when the frequency of the signal is high, the impedance of the capacitor 90 becomes small and N
A signal component is applied to the base of the PN transistor 83 via the resistor 89 and the capacitor 90. as a result,
The falling characteristic of the signal output from the emitter of the NPN transistor 81 is improved.

When the level of the video signal output from the emitter of the NPN transistor 81 becomes higher than the voltage set by the voltage source 44, the clamp diode 43 is turned on and the level thereof is prevented from becoming higher. .

Further, in the case where a predetermined amount or more of static electricity is accumulated in the cathode 41, discharge is performed by the discharge gap 42, and malfunction or damage due to static electricity is prevented.

Thus, in this embodiment, the NP
The N transistor 81 speeds up charging of the load capacitance 45, and the NPN transistor 83 speeds up discharging of the load capacitance 45.

Further, in the embodiment shown in FIG. 2, the capacitance component connected in parallel to the load resistor 38 is only the feedback capacitance C _re of the NPN transistor 81. As described above, in the case of FIG. 7, not only the feedback capacitance C _re of the NPN transistor 62 but also the PNP transistor 6
There is a feedback capacitance C _{re of} 3. Therefore, in the case of the embodiment shown in FIG. 2, compared with the case where the feedback capacitance C _re is shown in FIG.
It becomes 1/2.

From the above, the feedback capacitance C _re is prevented from obstructing the broadening of the band, and the load capacitance 4
By increasing the charging / discharging speed of 5, it is possible to achieve a wider band.

FIG. 3 shows the waveform of the video signal output from the emitter of the NPN transistor 81 and output to the cathode 41. As shown in the figure, the rising time tr has good characteristics close to the ideal waveform shown by the solid line.

On the other hand, the resistor 89 and the capacitor 90
When the NPN transistor 83 is not provided (when the NPN transistor 83 is always operated as a constant current source), the waveform is blunted and the fall time tf becomes long. However, if the high frequency component is applied to the base of the NPN transistor 83 via the resistor 89 and the capacitor 90, the fall time tf is shortened and a characteristic close to an ideal waveform can be realized.

In the embodiment shown in FIG. 2, more excellent high frequency characteristics can be realized with the same circuit power consumption as that of the conventional circuit. It is possible to reduce power consumption.

Further, since the embodiment of FIG. 2 is composed of transistors of the same junction type, it is easy to manufacture. In particular, since it can be composed of only NPN transistors, it can be made into a monolithic IC and the cost can be reduced.

FIG. 4 shows another embodiment. In this embodiment, the signal input terminal 31 is connected to the base of the NPN transistor 83 via the resistor 89 and the capacitor 90. That is, the signal input from the signal input terminal 31 passes through the resistor 89 and the capacitor 90,
It is adapted to be directly supplied to the base of the N-transistor 83. Therefore, the path for applying the high frequency component of the signal from the collector of the NPN transistor 81 to the base of the NPN transistor 83 is omitted, and the resistor 82 connected to the collector of the NPN transistor 81 is also omitted. Other configurations are similar to those in FIG.

Also in this embodiment, the same operation as in the case of FIG. 2 is executed and the same effect can be obtained only by the path of the feedforward of the high frequency component of the input signal to the base of the NPN transistor 83 being different. .

In the above description, the case where the present invention is applied to a monitor device for a computer is taken as an example, but the present invention is a monitor device for displaying a normal television signal,
It can be applied to a television receiver.

[0045]

As described above, according to the amplifying circuit, the cathode ray tube driving device and the display device of the present invention, the signal amplified by the cascode-connected first active element and the second active element is converted into the third amplifying element. Since the fourth active element connected to the third active element is operated as a constant current source that generates a constant current including a component that changes corresponding to the high frequency component of the signal, In addition, it is possible to reduce the influence of the feedback capacitance and widen the band at low cost.

According to the amplifying circuit of the second aspect, the first
Since the fourth active element has the same junction type, the structure is simplified and the manufacturing is facilitated.

According to the amplifier circuit of the third aspect, the first circuit
Since all the fourth active elements are composed of NPN transistors, a monolithic IC can be realized.
Cost reduction can be achieved.

According to the amplifier circuit of the fourth aspect, the third circuit
Since the high frequency component of the signal is supplied from the active element to the fourth active element, it is possible to reliably generate a constant current that changes in response to the high frequency component of the signal in the fourth active element. Become.

According to the amplifier circuit of the fifth aspect, since the high frequency component of the signal is supplied from the signal input terminal to the fourth active element, the fourth active element corresponds to the high frequency component of the signal. It is possible to reliably generate a constant current that changes with time.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a monitor device to which an amplifier circuit of the present invention is applied.

FIG. 2 is a circuit diagram showing a configuration example of an amplifier circuit 12R of FIG.

FIG. 3 is a waveform diagram showing characteristics of an amplifier circuit 12R of FIG.

FIG. 4 is a circuit diagram showing another configuration example of the amplifier circuit 12R of FIG.

FIG. 5 is a circuit diagram showing a configuration example of a conventional amplifier circuit.

6 is a waveform chart showing the characteristics of the example of FIG.

FIG. 7 is a circuit diagram showing another configuration example of a conventional amplifier circuit.

8 is a waveform chart showing the characteristics of the example of FIG.

[Explanation of symbols]

 1 Computer 2 Keyboard 3 Hard Disk 4 Monitor Device 1R, 1G, 1B D / A Converter 11R, 11G, 11B Amplitude Adjusting Circuit 12R, 12G, 12B Amplifying Circuit 13 Cathode Ray Tube 13R, 13G, 13B Cathode 32, 37 NPN Transistor 41 Cathode 45 load capacity 62 NPN transistor 63 PNP transistor 81,83 NPN transistor

Claims (7)

[Claims] 1. A first active element to which a signal input from a signal input terminal is supplied, and a cascode connection to the first active element, which amplifies and outputs a signal input from the signal input terminal. A second active element, a third active element that amplifies and outputs a signal output from the second active element, and a signal connected to the third active element and input from the signal input terminal A fourth active element that operates as a constant current source that generates a constant current that includes a component that changes in accordance with the high frequency component of 1. 2. The amplifier circuit according to claim 1, wherein the first to fourth active elements are of the same junction type. 3. The amplifier circuit according to claim 2, wherein the first to fourth active elements are all NPN transistors. 4. The amplifier circuit according to claim 3, wherein a high frequency component of a signal input from the signal input terminal from the third active element is supplied to the fourth active element. . 5. The amplifier circuit according to claim 3, wherein the fourth active element is supplied from the signal input terminal with a high-frequency component of a signal input thereto. 6. A cathode ray tube driving device for amplifying a video signal and supplying it to a cathode of a cathode ray tube or a first grid, comprising: a first active element to which the video signal input from a signal input terminal is supplied; A second active element that is cascode-connected to the first active element and that amplifies and outputs the video signal input from the signal input terminal; and an amplifier that amplifies the video signal output from the second active element. And a third active element for outputting as a constant current, which is connected to the third active element and generates a constant current including a component that changes corresponding to a high frequency component of the video signal input from the signal input terminal. And a fourth active element that operates as a source. 7. A display device comprising: a cathode ray tube for displaying an image; and an amplifier circuit for amplifying a video signal and supplying it to a cathode or a first grid of the cathode ray tube, wherein the amplifier circuit receives an input from a signal input terminal. A first active element to which the generated video signal is supplied; and a second active element that is cascode-connected to the first active element and that amplifies and outputs the video signal input from the signal input terminal. A third active element for amplifying and outputting the video signal output from the second active element, and a high frequency of the video signal input to the signal input terminal, the high frequency being connected to the third active element And a fourth active element that operates as a constant current source that generates a constant current containing a component that changes in accordance with the component.