JPH06205241A - Amplifier circuit for video signal - Google Patents

Abstract

PURPOSE:To suppress the fluctuation of an operating point due to a temperature characteristic without complicating the circuit configuration by providing a temperature characteristic correction circuit providing a temperature characteristic of an opposite polarity to that of a main amplifier section to an output voltage from a preamplifier section in the amplifier circuit. CONSTITUTION:A temperature characteristic correction circuit 9 is connected to a preamplifier section 1. The temperature characteristic correction circuit 9 is connected to a ground side of the preamplifier section 1 to cancel a potential fluctuation due to the temperature characteristic of the buffer amplifier 3 and the main amplifier section 4. Then the fluctuation of the operating point due to the temperature characteristic of the main amplifier section 4 is suppressed by the video signal use amplifier circuit. Moreover, since a power supply voltage Vcc applied to the main amplifier section 4 is enough to be a required minimum voltage to which a change in the operating point due to the temperature characteristic of the main amplifier section 4 is not added in this video signal amplifier circuit, the dynamic range is effectively utilized and the power consumption is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal amplifier circuit for amplifying a video signal in a television device or the like.

[0002]

2. Description of the Related Art Conventionally, in a television device, R
The three primary color signals, which are the video signals output from the GB matrix circuit, are amplified by the video signal amplifier circuit, and the CRT is displayed.
(Cathode ray tube). As shown in FIG. 2, the video signal amplifier circuit includes a preamplifier section 1 and a main amplifier section 4. That is, the three primary color signals (R, G, B) are input to the input terminals 10R, 10G, 1
It is input corresponding to 0B and supplied to the preamplifier section 1. The preamplifier unit 1 uses a so-called pedestal clamp, blanking,
Signal processing for contrast control, bright control, etc. is performed and sent to the main amplifier section 4 via the ATT circuit 2 and the buffer amplifier 3.

The main amplifier section 4 inverts and amplifies each of the sent primary color signals with a gain of about 15 times, a capacitor 5 for blocking a DC component and an adder 6 for adding a semi-fixed voltage.
It is sent to the CRT 8 via R, 6G, 6B.

The CRT 8 displays an image according to the sent three primary color signals.

[0005]

In the video signal amplifier circuit as described above, the preamplifier section 1 is used.
The main amplifier section 4 and the main amplifier section 4 are so-called DC coupled. Therefore, the temperature characteristic between the preamplifier 1 and the main amplifier unit 4 affects the operating point of the main amplifier unit 4. For example, the temperature characteristics of the buffer amplifier 3 and the main amplifier unit 4 are −2 mV, respectively.
/ Deg (° C) and the buffer amplifier is NP
If it is an N-type transistor, Tj = 20 ° C. to Tj
In the change of 120 ° C, a change of about 400 mV occurs as shown by an arrow A in FIG. If the gain of the main amplifier section 4 is 15 times, the operating point of the main amplifier section 4 is as shown by the arrow B in FIG.
It will be changed by 6V.

Therefore, the power supply voltage V _CC supplied to the main amplifier section 4 is a voltage obtained by adding 6 V, which is the change due to the temperature characteristics as described above. Therefore, the power consumption of the main amplifier unit 4 increases by 1.75 W when R _L = 1.2 kΩ.

On the other hand, when the buffer amplifier 3 is a PNP type transistor, the temperature characteristics of the main amplifier section 4 are canceled, but the input potential to the main amplifier section 4 rises by 2V _BE , that is, 1.4V. As a result, the output voltage of the main amplifier section 4 drops by 21V. It is difficult to correct this drop in potential.

It is considered that the output voltage of the main amplifier section 4 is fed back to the preamplifier section 1 to cancel the temperature characteristic, but the circuit configuration becomes complicated,
This leads to complication of manufacturing.

Therefore, the present invention has been proposed in view of the above circumstances, and is a video signal capable of suppressing the variation of the operating point due to the temperature characteristics without complicating the circuit configuration. It is an object of the present invention to provide an amplifier circuit for use.

[0010]

In order to solve the above problems and achieve the above objects, a video signal amplifier circuit according to the present invention is a preamplifier section to which a video signal is supplied and which performs signal processing on the video signal. A main amplifier unit that is DC-coupled to the preamplifier unit and is supplied with a video signal that has passed through the preamplifier unit, amplifies the video signal and supplies it to the display unit, and the main amplifier unit outputs the output voltage of the preamplifier unit. And a temperature characteristic correction circuit that gives a temperature characteristic of opposite polarity.

Further, according to the present invention, in the above-mentioned video signal amplifier circuit, the temperature characteristic correction circuit has a ground potential of the preamplifier portion which corresponds to at least a change amount of an operating point due to a temperature characteristic of the main amplifier portion. Only, the temperature characteristic is changed in a canceling direction.

Further, according to the present invention, in each of the above-mentioned video signal amplifier circuits, the temperature characteristic correction circuit is a PNP having an emitter terminal connected to a ground potential portion of the preamplifier portion.
It is configured to have a type transistor.

Further, according to the present invention, in each of the above-mentioned video signal amplifier circuits, the preamplifier section is connected to a three-terminal regulator for maintaining the supply voltage to the preamplifier section at a constant voltage. Is.

[0014]

In the video signal amplifier circuit according to the present invention,
Since the temperature characteristic correction circuit gives the output voltage of the preamplifier section which performs the signal processing to the supplied video signal, the temperature characteristic of the polarity opposite to that of the main amplifier section DC-coupled to the preamplifier section. Fluctuations in operating point due to temperature characteristics can be suppressed.

Further, in this video signal amplifier circuit,
In the case where the temperature characteristic correction circuit changes the ground potential of the preamplifier unit in the direction of canceling the temperature characteristic by at least the potential corresponding to the change of the operating point due to the temperature characteristic of the main amplifier unit, The power supply voltage supplied to the main amplifier unit can be suppressed to a necessary minimum.

Furthermore, in these video signal amplifier circuits, when the temperature characteristic correction circuit is configured to include a PNP type transistor having an emitter terminal connected to the ground potential portion of the preamplifier portion. Can realize the above operation with a simple circuit configuration.

In these video signal amplifier circuits, when a three-terminal regulator is connected to the preamplifier section, the voltage applied to the preamplifier is kept constant while the temperature characteristics of the main amplifier are corrected.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. A television device to which the video signal amplifier circuit according to the present invention is applied has a tuner for receiving broadcast radio waves of VHF, UHF, BS and the like via an antenna. The broadcast radio wave received by the tuner is converted to an intermediate frequency by the tuner, sent to the video detection circuit, and demodulated into a composite video signal by the video detection circuit. This composite video signal is sent to the Y / C separation circuit via a video switch or the like. The Y / C separation circuit separates the sent video signal into a luminance signal Y and a chroma signal C, sends the luminance signal Y to the luminance signal processing circuit, and sends the chroma signal C to the color demodulation circuit. The luminance signal Y is sent to the RGB matrix circuit after being subjected to signal processing such as sharpness processing and DC transmission rate conversion in the luminance signal processing circuit.
The chroma signal C is converted into BY, R by the color demodulation circuit.
-Y color difference signals are converted and sent to the RGB matrix circuit.

The RGB matrix circuit generates the three primary color signals R, G, B of the image signals, red, green and blue, from the transmitted luminance signal Y and color difference signals BY, RY. To the video signal amplifier circuit according to.

The video signal amplifier circuit according to the present invention is shown in FIG.
As shown in FIG. 3, it has a preamplifier section 1 and a main amplifier section 4. In the preamplifier section 1, the three primary color signals R, G, B are supplied to the input terminals 10R, 10G, 10B via the input terminals 10R, 10G, 10B.
Is input corresponding to. The preamplifier unit 1 performs signal processing on the supplied three primary color signals R, G, B for so-called pedestal clamp, blanking, contrast control, bright control, and the like.

The three-color primary color signals R, G, B output from the preamplifier section 1 are sent to the main amplifier section 4 via an ATT circuit 2 and a buffer amplifier (emitter follower) 3. The ATT circuit 2 includes an ATT circuit 2R for R for red primary color signal and an A for G for green primary color signal.
TT circuit 2G and ATT circuit 2B for blue primary color signal B
It consists of Further, the buffer amplifier 3 is
It is composed of an R buffer amplifier 3R for the red primary color signal, a G buffer amplifier 3G for the green primary color signal, and a B buffer amplifier 3B for the blue primary color signal. These buffer amplifiers 3R, 3G, 3B are composed of NPN type transistors.

Then, the main amplifier section 4 inverts and amplifies each of the sent primary color signals R, G and B with a gain of about 15 times. The power supply voltage V _CC is supplied to the main amplifier section 4.

The main amplifier section 4 is constructed for each of the primary color signals R, G, B, that is, for example, it has a total of three channels of amplification sections having the same configuration. As shown in FIG. 4, this amplification section has a first transistor 37 (NPN type: Q ₁ ) to which the primary color signal is supplied to the base terminal via the input terminal 38. The emitter terminal of the first transistor 37 is connected to the ground terminal 39 via the _first resistor (R ₁ ) 40.
Grounded through. This first transistor 37
The collector terminal of the second transistor 35 (NPN
It is connected to the emitter terminal of the type: Q ₂ ). This second
The transistor 35 has a base terminal to which the voltage V _BB is applied and a collector terminal to which the first resistor (R ₂ ) 32 and the first resistor (R ₂ ) 32 are connected.
Diode (D ₁ ) 34, second diode (D ₂ )
The power supply voltage V _CC is supplied via 33 and the power supply terminal 31. The collector terminal of the second transistor 35 is connected to the third transistor 41 (PNP type: Q
₃ ) Base terminal is connected. The collector terminal of the third transistor 41 is connected to the ground terminal 39, and the emitter terminal is connected to the output terminal 45 via the _third resistor (R ₃ ) 43. The power supply voltage V _CC is equal to the fourth transistor 42 (NPN type:
It is supplied to the collector terminal of Q ₄ ). The base terminal of the fourth transistor 42 is the second resistor 32.
Via the fourth resistor (R ₄ ) 44, and the emitter terminal is connected to the power supply terminal 31 via the output terminal 4
Connected to 5.

The primary color signals R, G, B amplified by the main amplifier section 4 have their direct current components cut off by a direct current component cutoff capacitor 5, and then a semi-fixed voltage source 7R,
A voltage corresponding to the cutoff voltage corresponding to each color in the CRT (cathode ray tube) 8 from 7G, 7B is added by the adders 6R, 6
The added video signals are added by G and 6B and sent to the CRT 8 as a DC reproduced video signal. In addition, the capacitor 5
Is composed of an R capacitor 5R for a red primary color signal, a G capacitor 5G for a green primary color signal, and a B capacitor 5B for a blue primary color signal.

Then, the CRT 8 displays a color image according to the sent three primary color signals R, G, B.

A temperature characteristic correction circuit 9 is connected to the preamplifier section 1. The temperature characteristic correction circuit 9 is connected to the ground side of the preamplifier unit 1 and has a potential fluctuation amount (each V _BE , a total of 2 in V _BE due to temperature characteristics of the buffer amplifier 3 and the main amplifier unit 4).
V _BE ) is offset.

As shown in FIG. 3, the temperature characteristic correction circuit 9 includes a first transistor 29 (PNP) whose emitter terminal is connected to the ground terminal of the preamplifier section 1 via a first connection terminal 28. Mold: Q ₁ ). The collector terminal of the first transistor 29 is connected to the power supply terminal of -5V or is grounded. This first
The power supply 27 is connected to the base terminal of the transistor 29 of the above through the _first diode (D ₁ ) 26, and the voltage V
_Has been supplied with ₀ . In addition, the first transistor 2
A bias voltage of 12 V is supplied to the base terminal of 9 through the _first resistor (R ₁ ) 25. And
The emitter terminal of the first transistor 29 is grounded via the _first capacitor (C ₁ ) 30. Further, the second connecting terminal 22 is connected to the emitter terminal of the first transistor 29 via the _second resistor (R ₂ ) 24. The second connection terminal 22 is grounded via the _second capacitor (C ₂ ) 23. A signal from the ATT circuit 2 is supplied to the second connection terminal 22.

With such a temperature characteristic correction circuit, the ground potential of the preamplifier section 1 is changed according to the temperature change so as to cancel the temperature characteristics of the buffer amplifier 3 and the main amplifier section 4. That is, in this video signal amplifier circuit, the power supply voltage V _CC supplied to the main amplifier section 4 is the minimum necessary voltage that does not add the variation of the operating point due to the temperature characteristics of the main amplifier section 4. Good.

As shown in FIG. 5, the video signal amplifier circuit according to the present invention can be constructed by connecting the three-terminal regulator 13 to the preamplifier 12 which serves as the preamplifier section 1. That is, in this video signal amplifier circuit, the preamplifier 12 has the input terminals 10R, 10G, 1 similar to the circuits in the above-described embodiments.
The primary color signals R, G, B are supplied via 0B, and these primary color signals R, G, B are sent to the ATT circuit 2. Then, in this example, a power supply voltage is supplied to the power supply terminal of the preamplifier 12 via the three-terminal regulator 13. A power of 15 V, for example, is supplied to the three-terminal regulator 13. Further, in the preamplifier 12, as in the circuit in the above-described embodiment,
The first transistor 17 (PNP type: Q ₁ ), this first
Is connected to the base terminal of the transistor 17 of the power supply 20 for supplying the voltage V ₀ via the _first diode (D ₁ ) 19 and the temperature characteristic correction circuit including the capacitors 16 and 21. There is.

In the video signal amplifier circuit having the three-terminal regulator, the voltage applied to the preamplifier 12 is corrected while the temperature characteristics of the buffer amplifier 3 and the main amplifier unit 4 are corrected. It can be constant.

[0031]

As described above, in the video signal amplifier circuit according to the present invention, the temperature characteristic correction circuit outputs the output voltage of the preamplifier section which performs signal processing to the supplied video signal to the preamplifier section. It gives a temperature characteristic of a polarity opposite to that of the DC-coupled main amplifier section. Therefore, in this video signal amplifier circuit, fluctuations in the operating point due to the temperature characteristics of the main amplifier section can be suppressed.

Further, in this video signal amplifier circuit,
In the case where the temperature characteristic correction circuit changes the ground potential of the preamplifier unit in the direction of canceling the temperature characteristic by at least the potential corresponding to the change of the operating point due to the temperature characteristic of the main amplifier unit, The power supply voltage supplied to the main amplifier part can be suppressed to the necessary minimum,
It is possible to effectively use the dynamic range and reduce power consumption.

Furthermore, in these video signal amplifier circuits, when the temperature characteristic correction circuit is configured to include a PNP type transistor having an emitter terminal connected to the ground potential portion of the preamplifier portion. Can realize the above operation with a simple circuit configuration.

In these video signal amplifier circuits, when a three-terminal regulator is connected to the preamplifier section, the voltage applied to the preamplifier is kept constant while the temperature characteristics of the main amplifier are corrected.

That is, the present invention can provide a video signal amplifier circuit capable of suppressing the variation of the operating point due to the temperature characteristics without complicating the circuit configuration.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a configuration of a video signal amplifier circuit according to the present invention.

FIG. 2 is a block circuit diagram showing a configuration of a conventional video signal amplifier circuit.

FIG. 3 is a circuit diagram showing a configuration of a temperature characteristic correction circuit of the video signal amplifier circuit according to the present invention.

FIG. 4 is a circuit diagram showing a configuration of a main amplifier section of the video signal amplifier circuit.

FIG. 5 is a block circuit diagram showing an example in which the video signal amplifier circuit according to the present invention is configured using a three-terminal regulator.

FIG. 6 is a waveform diagram showing a change in input potential to the main amplifier section due to temperature characteristics in the conventional video signal amplifier circuit.

FIG. 7 is a waveform diagram showing variations in the output potential of the main amplifier section due to temperature characteristics in the conventional video signal amplifier circuit.

[Explanation of symbols]

 1 ・ ・ ・ ・ ・ ・ ・ ・ ・ Pre-amplifier part 4 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Main amplifier part 8 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ CRT 9 ・ ・ ・ ・・ ・ ・ ・ ・ ・ ・ ・ Temperature characteristic correction circuit ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Three-terminal regulator 29 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ First transistor

Claims (4)

[Claims] 1. A video signal is supplied, and a preamplifier section that performs signal processing on the video signal, and a video signal that has been DC-coupled to the preamplifier section and that has passed through the preamplifier section are supplied with the video signal. A video signal amplifier circuit comprising: a main amplifier unit that amplifies and supplies the display unit with a temperature characteristic correction circuit that gives a temperature characteristic of a polarity opposite to that of the main amplifier unit to the output voltage of the preamplifier unit. 2. The temperature characteristic correction circuit changes the ground potential of the preamplifier section in a direction to cancel the temperature characteristic by at least a potential corresponding to a change in the operating point due to the temperature characteristic of the main amplifier section. Item 1. An amplifier circuit for video signals according to item 1. 3. The video signal amplifier circuit according to claim 1 or 2, wherein the temperature characteristic correction circuit includes a PNP transistor having an emitter terminal connected to a ground potential portion of the preamplifier portion. 4. The amplifier circuit for video signals according to claim 1, wherein the preamplifier section is connected to a three-terminal regulator for maintaining the voltage supplied to the preamplifier section at a constant voltage.