JPH0746048A - Video output device - Google Patents

Abstract

PURPOSE:To perform low power consumption by outputting a small amplitude video signal having a temperature dependency characteristic from a sub-amplifying stage to a main amplifying stage, canceling the temperature dependency characteristic of an NPN type transistor driven by the video signal and reducing the value of current at the time of outputting a block signal. CONSTITUTION:The pedestal level of an input synthesizing video signal VIN is conformed to that of reference voltage V22 in a pedestal clamp circuit 24, the signal is adjusted according to the signal of a terminal P23 in a contrast adjusting circuit 25 and the signal is transmitted to a load resistor R24. At this time, the current set by a temperature characteristic correction circuit 27 is introduced in a current source I26 for correction and the DC level of the signal VIN is shifted, in the resistor R24. This shift amount becomes the amount corresponding to the forward direction drop voltage of transistors Q28 and Q21, and the temperature characteristic which is reverse to the temperature characteristic of the transistor Q21 remains in the black level of the signal VIN outputted from an output circuit 26 to a power drive amplifier 23. Thus, the residual temperature characteristic of the signal VIN is canceled, a black level temperature characteristic is eliminated, the current at the time of outputting the black signal is reduced, and low power consumption is attained.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology (FIG. 6) Problem to be Solved by the Invention (FIG. 7) Means for Solving the Problem (FIGS. 1 to 5) Action Example (FIGS. 1 to 5) (1) First Embodiment (FIG. 1) (1-1) Configuration of Embodiment (1-1-1) Overall Configuration (1-1-2) Configuration of Pedestal Clamp Circuit 24 and Contrast Adjustment Circuit 25 (1-1- 3) Output circuit 26 and temperature characteristic correction circuit 27
(1-2) Operation and effect of the embodiment (2) Second embodiment (Fig. 2) (2-1) Structure of the embodiment (2-1-1) Overall structure (2-1-2) Output circuit 34 and temperature characteristic correction circuit 35
(2-2) Operations and effects of the embodiment (3) Other embodiments (FIGS. 3 to 5) Effects of the invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video output device, for example, a cathode ray tube (hereinafter CRT: cath) which requires high resolution.
It is suitable for application to a display drive (called an oderay tube).

[0003]

2. Description of the Related Art Conventionally, as a drive circuit for a CRT display, a drive circuit having a structure shown in FIG. 6 has been used. The video output circuit 1 is composed of a two-stage amplifier circuit of a pre-drive amplifier 2 and a power drive amplifier 3, and outputs a composite video signal V _IN amplified in each stage to a CRT display 4. . The pre-drive amplifier 2 is composed of a monolithic integrated circuit. This circuit is provided with a terminal P ₁ for inputting a video signal and terminals P ₂ and P ₃ for adjusting contrast and brightness, and an image output corresponding to the adjustment signal is output from the terminal P ₄ . .

On the other hand, the power drive amplifier 3 is composed of a hybrid integrated circuit. The power drive amplifier 3 is an inverting type amplifier circuit, and the gain is set by resistors R1 and R2 connected to the input / output terminals of the operational amplifier circuit 3A. This kind of power drive amplifier 3
Is formed so as not to have temperature dependence in terms of both DC and AC, and the DC component (that is, black level) of the composite video signal V _IN output from the pre-drive amplifier 2 has a temperature dependence characteristic. It is made not to. A diode D1 for setting a sync tip level and a variable voltage source V1 are connected to a midpoint of connection between the power drive amplifier 3 and the CRT display 4.

[0005]

However, when the power drive amplifier is constructed by such a hybrid integrated circuit, there is a problem that the cost becomes high, and there is a problem that the output dynamic range is limited by the power supply voltage. Atsuta Therefore, as shown in FIG. 7, a video output circuit 11 in which a power drive amplifier 13 which is a discrete component is connected to a pre-drive amplifier 12 has been put into practical use. Incidentally, the terminals P ₁₁ , P ₁₂ and P ₁₃ of the pre-drive amplifier 12 indicate an input terminal, a contrast adjustment terminal and an output terminal, respectively.

This power drive amplifier 13 has a first-stage P
The output of the NP-type transistor Q ₁₁ (generated in the resistor R ₁₂ ) is amplified by the NPN-type power transistor Q ₁₂ provided in the subsequent stage, and the CRT is connected via the transistor Q ₁₃ cascade-connected to the power transistor Q _12. The composite video signal V _IN (generated in the resistor R ₁₄ ) is output to the display 4. The gain is the ratio of the resistance R ₁₃ connected to the emitter of the power transistor Q ₁₂ and the resistance R ₁₃ connected to the collector of the transistor Q ₁₃ (R ₁₄ /
R ₁₃ ). As described above, the power drive amplifier 13 combines the PNP type transistor Q ₁₁ and the NPN type power transistor Q ₁₂ and cancels the temperature dependence characteristic of the black level by the forward voltages V _BE in the opposite directions.

However, the PNP type transistors Q ₁₁ and N
Forward voltage V _BE with PN type power transistor Q ₁₂
Power drive amplifier 13
It was not possible to cancel out the temperature-dependent characteristics of the two.
Therefore, the composite video signal V _IN output from the power drive amplifier 13 may have a temperature-dependent characteristic.
Further, when the output stage of the pre-drive amplifier 12 is formed by the complementary output stage, the output potential (emitter potential) of the power transistor Q ₁₂ cannot be lowered (that is, it can be lowered below about 2VBE). However, there is a drawback that the current flowing in the black level signal portion becomes large and the power consumption becomes large.

The present invention has been made in consideration of the above points, and an object thereof is to propose a video output device capable of further reducing the power consumption of the main amplification stage at the time of black level output.

[0009]

In order to solve such a problem, according to the present invention, a large-amplitude video signal amplified by the sub-amplifying stage drives the NPN transistor Q ₂₁ of the main amplifying stage 23 to a large level. In a video output device that generates a video signal of amplitude and drives the picture tube 4 by the video signal of large amplitude, the video signal of small amplitude output from the sub-amplification stage 22 is given a temperature-dependent characteristic, The temperature-dependent characteristic of the main amplification stage 23 is compensated by driving the NPN transistor Q ₂₁ in the main amplification stage 23 by the video signal having the dependence characteristic.

Further, in the present invention, the NPN transistor Q ₂₁ of the main amplification stage 43 is driven by the small amplitude video signal amplified by the sub amplification stage 42 to generate a large amplitude video signal, and the large amplitude video signal is generated. In the video output device that drives the picture tube 4 by the video signal of the amplitude, the voltage level of the final output stage that constitutes the main amplification stage 43 is fed back to the sub amplification stage 42, and the sub amplification stage is based on the voltage level. The small-amplitude video signal output from 42 is provided with a temperature-dependent characteristic, and the large-amplitude video signal output from the main amplification stage 43 is canceled.

[0011]

[Action] The small amplitude of the video signal having a temperature dependent characteristic output from the sub-amplifier stage 22, 42 to the main amplifier stage 23 and 43, NPN-type transistor Q ₂₁ which is by connexion drive to the video signal
The temperature dependence of is canceled out. NPN at this time
Since the type transistor Q ₂₁ is driven by the output of the sub-amplifying stage 22, the emitter potential of the NPN type transistor at the black level can be lowered. As a result, the amount of current can be reduced, and the power consumption of the main amplification stage can be further reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) First Embodiment (1-1) Structure of the Embodiment (1-1-1) Overall Structure In FIG. 1 in which parts corresponding to those in FIG. A CRT display video output circuit is shown as, and is configured by a two-stage amplification circuit of a pre-drive amplifier 22 and a power drive amplifier 23. The video output circuit 21 is configured to cancel out the temperature dependence characteristic of the power drive amplifier 23 by positively giving the temperature dependence characteristic to the composite video signal V _IN output from the pre-drive amplifier 22.

The power drive amplifier 23 is composed of discrete components, and is used as the predrive amplifier 2.
The composite video signal V _IN output from 2 is directly input to the NPN type power transistor Q ₂₁ .
Similarly, an NPN transistor Q ₂₂ is cascade-connected to the collector of the power transistor Q ₂₁ . The transistor Q ₂₂ functions so that the frequency characteristic is not deteriorated by the mirror effect of the capacitance C _CB between the collector and the base of the power transistor Q ₂₁ and the output resistance R ₂₂ .

On the other hand, the pre-drive amplifier 22 comprises a pedestal clamp circuit 24, a contrast adjusting circuit 25 and an output circuit 26. The pre-drive amplifier 22 receives the composite video signal V _IN input to the input terminal P ₂₁ from the pedestal clamp circuit 24 and the contrast adjustment circuit 2.
5 and the output circuit 26 in order, and then output from the output terminal P ₂₂ to the power drive amplifier 23 in the subsequent stage.

Further, the predrive amplifier 22 has a temperature characteristic correction circuit 27 built therein. The temperature characteristic correction circuit 27 intended to have a positive temperature dependence on the mixed video signal V _IN applied to the output circuit 26 from the contrast adjustment circuit 25, the power transistor in the mixed video signal V _IN to be outputted from the output circuit 26 It is designed to have a temperature characteristic opposite to that of Q ₂₁ .

(1-1-2) Pedestal clamp circuit 2
4 and the configuration of the contrast adjustment circuit 25 The pedestal clamp circuit 24 inputs the composite video signal V _IN from the input terminal P _{21 and} the contrast adjustment circuit 2 in the subsequent stage.
5 and a differential amplifier 24B that controls the feed back so that the pedestal level of the composite video signal V _IN output to the contrast adjusting circuit 25 matches the reference voltage V ₂₂ .

The contrast adjusting circuit 25 comprises a differential amplifier stage 2 composed of a pair of transistors Q ₂₃ and Q ₂₄ .
5A and a pair of transistors Q ₂₅ and Q ₂₆ , and a differential amplification stage 25B, which is a two-stage differential amplification circuit. Here, current sources I ₂₁ and I ₂₂ are connected to the common emitters of the transistors Q ₂₃ and Q _{24 and} the common emitters of the transistors Q ₂₅ and Q ₂₆ , respectively, of which the common emitters of the transistors Q ₂₃ and Q ₂₄ and the current source I ₂₂ are connected. _A composite video signal V _IN is applied to the midpoint of connection with ₂₁ via a resistor R ₂₃ . As a result, the differential amplification stage 25
A signal current that increases and decreases according to the composite video signal V _IN flows through A.

[0019] Control voltage ΔV to the base of the base and the transistor Q _25, Q ₂₆ of the transistors Q _23, Q ₂₄ constituting a pair of differential pair is given from the respective control voltage generating circuit 25C. This control voltage ΔV can be changed by the adjustment signal applied to the contrast adjustment terminal P ₂₃ , so that the current ratio of the currents flowing through the transistors Q ₂₃ , Q ₂₄ and the transistors Q ₂₅ , Q ₂₆ can be switched. Has been done.

As a result, the amount of signal current drawn into the contrast adjusting circuit 25 from the load resistor R ₂₄ to the collectors of the transistors Q ₂₄ and Q ₂₅ connected to each other via the transistor Q ₂₃ is increased or decreased. .
The output terminal of the contrast adjustment circuit 25 and the load resistance R ₂₄
The transistor Q ₂₇ connected between
The collector capacitances of ₂₄ and Q ₂₅ are apparently reduced to widen the band.

(1-1-3) Configuration of Output Circuit 26 and Temperature Characteristic Correction Circuit 27 The output circuit 26 inputs the voltage generated in the load resistor R ₂₄ via the buffer amplifier 28 and is of NPN type than the resistor R ₂₅ . It is adapted to be input to the base of the transistor Q ₂₈ . The transistor Q ₂₈ is grounded to the emitter, and the composite video signal V _IN is output from the midpoint of the connection between the emitter and the current source I ₂₄ via the terminal P ₂₂ . Further, a current source I ₂₃ is connected via a switch SW ₂₁ to the connection midpoint between the resistor R ₂₅ and the base of the transistor Q ₂₈ .

The switch SW ₂₁ is opened / closed by a blanking pulse BLK. That contrast switch the switch SW ₂₁ in the blanking period is controlled to a closed state, are adapted to switch the switch SW ₂₁ to the image input period (periods other than the blanking period) is controlled to the open state . As a result, the signal current in the video input period flows to the current source I ₂₄ via the transistor Q ₂₈ , whereas the signal current in the blanking period flows to the current source I ₂₃ via the switch SW ₂₁ .

The temperature characteristic correction circuit 27 has a temperature-dependent characteristic corresponding to the base-emitter voltage V _BE of the power transistor Q ₂₁ externally attached to the pre-drive amplifier 22 and the transistor Q ₂₈ provided in the pre-drive amplifier 22. The composite video signal V _IN input to the output circuit 26 is supplied. The temperature characteristic correction circuit 27 has a load resistance R _24.
The temperature dependence characteristic is canceled out from the current flowing in the power drive amplifier 23 by finely adjusting the amount of current flowing in the power drive amplifier 23 according to the temperature.

For fine adjustment of the amount of current flowing through the load resistor R ₂₄ , the correction current source I ₂₆ connected to the output terminal of the contrast adjusting circuit 25 is used. The temperature characteristic correction circuit 27 adjusts the amount of current flowing through the correction current source I ₂₆ . The temperature characteristic correction circuit 27 compares the black level of the composite video signal V _IN with the reference potential having temperature dependency by the differential amplifier 27A, and the correction current source I ₂₆ of the correction current source I ₂₆ is made to match the two input levels. It is designed to set the current value.

Here, the differential amplifier 27A compares the black level of the composite video signal V _IN supplied to the output circuit 26 with the reference potential only during the period when the clamp pulse CLP is rising so that the two potentials match. The output potential is set to. At this time, the clamp pulse CLP is designed to rise for a predetermined period of the blanking period during which the black level signal is input.

Further, the differential amplifier 27A is adapted to hold a black level corresponding to the reference potential in the capacitor C ₂₁ externally attached to the terminal P ₂₄ , and depending on the temperature while the video signal is being input. It is designed to allow current to flow. Further, the reference potential having temperature dependency is given by the transistor Q ₂₈ and the power amplifier Q ₂₁ in the integrated circuit by the same NPN type transistors Q ₂₉ and Q ₃₀ . The transistors Q ₂₉ and Q ₃₀ are diode-connected in which the base and collector are short-circuited, respectively, and the voltage corresponding to the forward voltage V _BE of the transistor Q ₂₈ and the power amplifier Q ₂₁ in the integrated circuit is connected in two stages. Transistors Q ₂₉ and Q ₃₀
It is designed to be generated by

Incidentally, the transistor Q ₂₉ for generating the reference potential is constantly supplied with the current I ₀ from the current source I ₂₅ connected to the collector, and the current I ₀ and the transistors Q ₂₉ and Q _29.
The combination of ₃₀ allows the transistor Q ₂₈ in the integrated circuit.
And a temperature characteristic corresponding to that of the power amplifier Q ₂₁ . Of the transistors Q ₂₉ and Q ₃₀ for generating the reference potential, the emitter of the transistor Q ₃₀ is the bright control terminal P via the attenuator 29.
_The reference level is increased or decreased by adjusting the voltage level of the variable voltage source V ₂₄ externally connected to the bright control terminal P ₂₅ .

(1-2) Operation and Effect of the Embodiment In the above-mentioned configuration, the driving of the CRT display 4 by the video output circuit 21 will be described focusing on the operating state of the power drive amplifier 23 by the pre-drive amplifier 22.
First, the composite video signal V _IN input to the video output circuit 21 is supplied to the pedestal clamp circuit 24 at a predetermined reference potential V _IN.
The pedestal level can be adjusted to ₂₂ . Composite video signal V _IN
Is then input to the contrast adjustment circuit 25 and a signal current corresponding to the composite video signal V _IN adjusted according to the adjustment signal applied to the contrast adjustment terminal P ₂₃ is applied to the load resistor R.
Flows to ₂₄ .

The addition to the signal current to the load resistor R ₂₄ In this case, the current had it occurred set to a temperature characteristic correction circuit 27 is drawn into the correction current source I _26, the correction current source I ₂₆
The DC level of the composite video signal V _IN is shifted by the amount of the current drawn in. This DC level shift is due to the forward drop voltage of the transistor Q ₂₈ and the power transistor Q
_This is the voltage value obtained by adding the ₂₁ forward voltage drops in the opposite direction.

Accordingly, the black level of the composite video signal V _IN output from the output circuit 26 to the power drive amplifier 23 still has a temperature characteristic opposite to the temperature characteristic of the power amplifier Q ₂₁ . After that, since the temperature characteristic remaining in the combined video signal V _IN is canceled by the transistor Q ₂₁ , the black level temperature characteristic is removed from the emitter potential of the power amplifier Q ₂₁ . As a result, the output of the pre-drive amplifier 22 is amplified by the resistance R ₂₂ corresponding to the output resistance of the power drive amplifier 23 by the value obtained by dividing the resistance value of the resistance R ₂₂ by the resistance R ₂₁ (= R ₂₂ / R ₂₁ ). Output with no temperature characteristic appears. At this time, the video output circuit 2
The first frequency band can operate up to about 100 [MHz], and the frequency characteristic can be extended to a wide band.

According to the above configuration, since it is not necessary to connect the PNP type transistor Q ₁₁ required in the conventional circuit to the circuit forming the power amplifier 23, it is possible to reduce the number of parts, and As described above, since the PNP type transistor Q ₁₁ is unnecessary, the cost can be reduced.
Further, since the power drive amplifier 23 is constructed by connecting discrete components, the output resistor R ₂₂
It is also possible to increase the voltage level of the power supply voltage V _CC connected to one end of the output voltage Vcc, and it is possible to easily extend the output dynamic range by giving a voltage of 100 [V], for example. Furthermore, since the emitter potential of the power transistor Q ₂₁ can be lower than the potential of the output terminal P ₂₂ when a black level signal is output, the amount of current flowing through the power transistor during this period can also be reduced. This further reduces the power consumption.

(2) Second Embodiment (2-1) Structure of the Embodiment (2-1-1) Overall Structure In FIG. 2 in which parts corresponding to those in FIG. A video output circuit is shown as, and the pre-drive amplifier 32 and the power drive amplifier 33 can drive the CRT display 4 of higher resolution. Here, the pre-drive amplifier 32 has the same configuration as the pre-drive amplifier 22 of FIG. 1 except for the output circuit 34 and the temperature characteristic correction circuit 35.

Further power drive amplifier 33 is adapted to connect the transistor Q ₃₁ of the emitter follower output at the preceding stage of the power transistor Q ₂₁ to improve the driving capability by supplying a current of several tens of [mA] The power transistor Q ₂₁ ing. This in a large current several tens [mA] also of the transistor Q ₂₁ increasing capacitance between the base and the emitter, only the output of the pre-drive amplifier 32 is because it may not be able to drive.

(2-1-2) Configuration of Output Circuit 34 and Temperature Characteristic Correction Circuit 35 In this example, the output stage of the output circuit 34 is composed of an NPN type transistor Q ₃₂ and a PNP type transistor Q _33. It is configured by a complementary push-pull output circuit. At this time, the power transistor Q ₂₁ is a two-stage NPN.
Type video signal V _IN via type transistors Q ₃₂ and Q ₃₁
Driven by.

Further the temperature characteristic correction circuit 35 is adapted to provide a reference potential having a temperature dependent characteristic by connexion differential amplifier 27A for cascading the transistors Q _34, Q ₃₅ and Q ₃₆ of 3-stage diode-connected There is. The temperature characteristic correction circuit 35 includes a transistor Q ₃₂ which forms an output stage of the output circuit 34 by the three stages of transistors Q ₃₄ , Q ₃₅ and Q ₃₆ , a transistor Q ₃₁ which forms a front stage of the power drive amplifier 33, and a power source. The temperature dependence characteristic of each forward voltage drop of the transistor Q ₂₁ is compensated.

(2-2) Operation and effect of the embodiment With the above configuration, driving of the CRT display 4 by the video output circuit 31 will be described. Also in this case, the pre-drive amplifier 32 outputs the composite video signal V _{IN which} is level-shifted by the voltage corresponding to the temperature characteristics of the driving transistor Q ₃₁ and the power transistor Q ₂₁ which constitute the power drive amplifier 33. Therefore, when it appears in the emitter of the power transistor Q ₂₁ via the transistor Q ₃₁ , the temperature dependent characteristic of the black level of the composite video signal V _IN is canceled and the output without the temperature dependent characteristic is output from the output resistor R ₂₂ to the CRT display 4. Will be done.

Generally, when the output stage of the predrive amplifier 32 is a complementary push-pull output stage, the output potential of the composite video signal V _IN output from the output end P ₂₂ is the current source I ₂₄ and the PNP transistor. It is not possible to lower the voltage between the base-emitter voltage of Q33 (that is, 2V _BE ) and the value (for example, 2 [V]) or less.
By forming the first stage of the power drive amplifier 33 with the NPN transistor Q ₃₁ , the emitter potential of the power amplifier Q ₂₁ can be lowered to about 0.6 [V]. This potential is 1.4 compared with the conventional circuit shown in FIG. 7 in which the output potential of the pre-drive amplifier 32 is directly applied.
[V] can be set lower.

As a result, the amount of current flowing through the power drive amplifier 33 can be reduced when the composite video signal V _{IN is at} the black level. As a result, it is possible to realize the power drive amplifier 33 that consumes less power than the conventional one. Further, as in the example, the power transistor Q ₂₁ of the power drive amplifier 33 is driven by the first-stage transistor Q ₃₁ , so that the frequency characteristic can be expanded to a high frequency band up to about 150 [MHz].

According to the above configuration, it is possible to realize the video output circuit 31 capable of driving the CRT display 4 in a wider band than the conventional one. As a result, it is possible to display an image with higher resolution.

(3) Other Embodiments In the above embodiment, the predrive amplifier 22 is used.
When the power amplifier 23 is directly driven by the output of the output circuit 26, the output circuit 26 forming the output stage of the pre-drive amplifier 22.
The case where the temperature-dependent characteristic is generated by taking in the black level of the composite video signal V _IN input to the temperature characteristic correction circuit 27 has been described (FIG. 1), but the present invention is not limited to this, and the power drive amplifier is used. The temperature-dependent characteristic may be generated in the current flowing through the load resistor R ₂₄ based on the voltage value returned to the pre-drive amplifier.

For example, as shown in FIG. 3, when the black level signal component of the composite video signal V _IN is output as it is through the transistor Q ₄₁ forming the output circuit 44, the emitter potential of the power transistor Q ₂₁ is set to the same value. It may be returned to the pre-drive amplifier 22.

In this case, the temperature characteristic correction circuit 45 has the terminal P
The emitter potential of the power transistor Q ₂₁ fed back via ₄₁ and the reference potential given via the attenuator 29 are compared by the differential amplifier 45A, and the current amount of the current source is adjusted so that the emitter potential matches the reference potential. Should be adjusted.

Further, as shown in FIG. 4, the composite video signal V _IN output from the power drive amplifier 53 to the CRT display 4 is fed back to the temperature characteristic correction circuit 45 of the predrive amplifier 52 via the attenuator 54. Is also good. By doing so, in addition to the above-mentioned effects, the influence of the temperature-dependent characteristics can be further reduced.

Further, in the above embodiment, when the power amplifier 23 is directly driven by the output of the predrive amplifier 22, the composite video signal V _IN input to the output circuit 26 constituting the output stage of the predrive amplifier 22 is input. Although the case where the temperature-dependent characteristic is generated by taking in the black level into the temperature characteristic correction circuit 27 and adjusting the amount of current flowing through the current source I ₂₆ has been described (FIG. 1), the present invention is not limited to this. load resistor R ₂₄ on the basis of the power drive amplifier as shown in the voltage value back to the pre-drive amplifier
It is also possible to adjust the value of the power supply voltage applied to the. Thus the load resistor R can be reduced the amount of current flowing to ₂₄ if a small transistor area of connected transistors Q ₂₇ for improvement of the frequency characteristics between the load resistor R ₂₄ and the contrast adjustment circuit 25 Things can be used. By doing so, the parasitic capacitance can be further reduced, and in addition to the above-mentioned effect, the frequency characteristic can be extended to a higher frequency band.

[0045]

As described above, according to the present invention, a small-amplitude video signal having a temperature-dependent characteristic is output from the sub-amplifying stage to the main amplifying stage, and is driven by the video signal. The temperature dependence of is canceled out. As a result, the emitter potential of the NPN transistor of the main amplification stage when the black signal is output is lowered, and the amount of current flowing at this time can be reduced. As a result, it is possible to easily realize a main amplification stage that consumes much less power than the conventional one.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of a pre-drive circuit according to the present invention.

FIG. 2 is a connection diagram showing an embodiment of a pre-drive circuit according to the present invention.

FIG. 3 is a connection diagram showing an embodiment of a predrive circuit according to the present invention.

FIG. 4 is a connection diagram showing an embodiment of a predrive circuit according to the present invention.

FIG. 5 is a connection diagram showing an embodiment of a pre-drive circuit according to the present invention.

FIG. 6 is a connection diagram showing a conventional pre-drive circuit.

FIG. 7 is a connection diagram showing a conventional predrive circuit.

[Explanation of symbols]

1, 11, 21, 31, 41, 51, 61 ... Video output circuit, 2, 12, 22, 32, 42, 52, 62 ... Pre-drive amplifier, 3, 13, 23, 33, 43, 5
3, 63 ... Power drive amplifier, 4 ... CRT display, 24 ... Pedestal clamp circuit, 25 ...
Contrast adjustment circuit, 26, 34, 44 ... Output circuit, 27, 35, 45 ... Temperature characteristic correction circuit, 28 ...
Buffer amplifier, 29, 54 ... Attenuator.

Claims (4)

[Claims] 1. A small-amplitude video signal amplified by a sub-amplification stage drives an NPN transistor of the main amplification stage to generate a large-amplitude video signal, and the large-amplitude video signal receives an image. In a video output device for driving a tube, the small amplitude video signal output from the sub-amplification stage has a temperature-dependent characteristic, and the NPN type in the main amplification stage is provided by a video signal having the temperature-dependent characteristic. An image output device characterized by compensating for the temperature dependence of the main amplification stage by driving a transistor. 2. The sub-amplifying stage, a contrast adjusting circuit, a load driven by an output current of the contrast adjusting circuit, and an emitter follower output for outputting the voltage generated in the load as the video signal of the small amplitude. A variable current source connected in series to the load, and a voltage generated in the load and a reference potential having a temperature dependent characteristic, and adjusting the amount of current flowing in the variable current source. The video output device according to claim 1, further comprising a temperature-dependent characteristic compensation circuit that shifts a voltage level generated in the load. 3. A sub-amplifying stage, a contrast adjusting circuit, a load driven by an output current of the contrast adjusting circuit, and an emitter follower output for outputting the voltage generated in the load as the video signal of the small amplitude. And a voltage generated in the load and a reference potential having a temperature-dependent characteristic are compared with each other, and the power-supply potential applied to one end of the load is increased or decreased to shift the voltage level generated in the load. The video output device according to claim 1, further comprising a compensation circuit. 4. A small-amplitude video signal amplified by the sub-amplification stage drives an NPN transistor of the main amplification stage to generate a large-amplitude video signal, and the large-amplitude video signal receives an image. In a video output device that drives a tube, the voltage level of the final output stage that constitutes the main amplification stage is fed back to the sub amplification stage, and the small-amplitude video output from the sub amplification stage based on the voltage level. A video output device characterized in that the signal has a temperature-dependent characteristic, and the temperature-dependent characteristic of the large-amplitude video signal output from the main amplification stage is canceled.