JPH10262263A - Signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively utilize a dynamic range of a signal input without extending the signal input dynamic range in a signal processing circuit. SOLUTION: A changeover switch 150 is switched based on a blanking signal source 48 to work for switching an input signal level to a DC level based on a DC lever control signal source 49 in the case of blanking. That is, the changeover switch 150 is in the side of an input terminal 100 usually to fetch an input signal. In the case of blanking, the changeover switch 150 is switched to the side of the DC level control signal source 49 only for a short period of time by a blanking signal that is generated for the short period and as the result the circuit is made into a form that a signal of which the DC level continues for a short time (DC pulse) is added to the input signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit suitable for controlling a video signal for driving a display such as a CRT display.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional example of a video amplifier circuit for a color CRT display. In the circuit shown in the figure, video signals of three primary colors of R (red), G (green), and B (blue) are supplied from respective signal sources 4R, 4G, 4B to video signal processing circuits 15R, 15G, 15B. Via C
It is added to the cathodes 3R, 3G, 3B of RT4.
In the CRT 4, the first grid 11 is divided into three primary colors RGB.
Is shared by

In the conventional example, since the same configuration is used in any of the three primary color circuits, the operation of the R color circuit 15R will be described as a representative. The input signal voltage Vir is applied to the base of the transistor 6R constituting the common-emitter amplifier circuit, and is inverted and amplified at its collector to become the output signal voltage Vor, which is applied to the cathode 3R of the CRT 4.

The operating point of the output signal voltage Vor at that time is adjusted using a variable resistor 8R for cutoff adjustment, and the voltage gain is adjusted using a variable resistor 9R for drive adjustment.
The adjustment range of the DC operating point of the output signal voltage is limited by the resistor 7R. The resistor 10R, like the resistor 7R, limits the voltage gain adjustment range described above.

[0005] The white balance adjustment in the above conventional example is as follows.
This has been achieved by repeatedly performing the cutoff adjustment of each primary color circuit and the drive adjustment of the video amplifier circuit of at least two primary colors.

The white balance adjustment process in the above conventional example will be described with reference to FIG. 5, which is an input / output characteristic diagram of a video amplifier circuit. In the characteristic diagram of FIG. 5, the input signal voltage is V
When i, the horizontal axis represents the input signal voltage Vi, and when the output signal voltage is Voo, the vertical axis represents the output signal voltage Voo, and the white line targeted by the characteristic line 50 shown by the solid line is secured. Input / output characteristics.

It is assumed that the white balance adjustment is achieved by performing cutoff adjustment and drive adjustment with the input signal voltage shown in FIG. 5 at the values of Vic and Vid. Assuming that the initial state of the video amplifier circuit has the characteristics shown by the broken line 51, the output voltage Voo is mainly level-shifted as shown by the arrow 52 by performing the first cutoff adjustment, and is shown by the broken line 53. Move to properties.

In the next drive adjustment, the voltage gain adjustment shown by the arrow 54 is performed, and the characteristic shown by the broken line 55 is obtained, and the first white balance adjustment is completed. However, as is apparent from the arrow 56 in FIG. 5, there arises a problem that the cutoff adjustment performed earlier is shifted by the drive adjustment.

[0009]

Therefore, in the conventional video amplifier circuit, since there is interference between the cutoff adjustment and the drive adjustment, the white balance adjustment cannot be completed unless these adjustments are repeated. There's a problem.

[0010] In the above conventional example, in FIG.
It is necessary to input signals over a wide voltage range including DC components to the video signal processing circuits 15R, 15G, and 15B. Therefore, the video signal processing circuits 15R, 15G, 15
B requires a wide input dynamic range. However, with the expansion of the input dynamic range, a wide output dynamic range and a high power supply voltage are required, and there is a problem that the power consumption of the circuit increases.

Accordingly, an object of the present invention is to provide a signal processing circuit capable of effectively utilizing a dynamic range without expanding a signal input dynamic range thereof in relation to the latter of the above two problems. It is in.

[Means for Solving the Problems]

In order to achieve the above object, in the signal processing circuit of the present invention, one input terminal of a changeover switch that switches based on a periodically generated signal, such as a blanking signal, is connected to one input terminal of a switch. A target input signal is input, and a DC signal whose level can be controlled, such as a DC level control signal for blanking, is input to the other input terminal of the changeover switch. Also, the input terminal of the DC component controller is connected to the output terminal of the changeover switch. Then, the output terminal of the DC component controller is connected to the output terminal of the signal processing circuit of the present invention.

[0013]

In the means for achieving the above object, the changeover switch is switched based on a signal generated at a fixed period, such as a blanking signal, and only when the blanking is performed during blanking. , The input signal level is switched to a DC level based on the DC level control signal to add a DC component. Further, the DC component controller newly controls the level of the DC component (added DC component) of the signal subjected to the switching process. By these means, the signal input dynamic range of the signal processing circuit can be effectively utilized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. One embodiment for achieving the object of the present invention is shown in FIG. In FIG. 1, an input signal to be processed is input to one input terminal of a changeover switch 150 that switches based on a blanking signal source 48 via an input terminal 100, and the other of the changeover switch 150 Input terminal receives a DC level control signal at the time of blanking,
9 is input. The changeover switch 15
The input terminal of the DC component controller 201 is connected to the 0 output terminal. Then, the output terminal of the DC component controller 201 is connected to the output terminal 101.

Next, the operation of the embodiment shown in FIG. 1 will be described. The changeover switch 150 is switched based on the blanking signal source 48, and functions to switch the input signal level to the DC level based on the DC level control signal source 49 at the time of blanking. That is, the changeover switch 150 is always used.
Is located at the input terminal 100 side and takes in the input signal. At the time of blanking, the blanking signal generated for a short period switches to the DC level control signal source 49 only for the short period, and as a result, , A signal (DC pulse) in which the DC level lasts for a short period is added to the input signal.

Therefore, at the time of blanking, a blanking pulse (DC pulse) is added to the input signal to be processed. Further, the DC component controller 201 newly controls the level of the DC component (DC pulse) of the signal subjected to the switching process. By these means, the signal input dynamic range of the signal processing circuit can be effectively utilized. In other words, the input dynamic range can include only a change range that includes both an AC component of a signal and a DC component by luminance control, which are minimum required for signal transmission.

Therefore, after the blanking pulse is added, the signal can be AC-coupled and transmitted. Further, it is possible not only to transmit the DC component of the input signal but also to newly control the DC component (luminance). For example, it is also possible to control the DC component of the signal for fixing the operating point described above. Further, by providing a DC component reproducing circuit including a clamp circuit immediately before the driving terminal of the picture tube, the power supply voltage and power consumption of the video output amplifier can be reduced.

Next, FIG. 2 shows an embodiment in which the second object is achieved by applying the present invention to a video signal amplifier circuit. In FIG. 2, an inverting amplifier 63 is connected to the output terminal of a changeover switch 150 that switches based on a blanking signal source 67, and a DC component comprising a capacitor 64 and a switch 68 is provided downstream of the inverting amplifier 63. By arranging the circuit 201A, a video signal amplifier circuit is formed.

The changeover switch 150 is switched on the basis of the blanking signal source 67 and functions to switch the input signal level to a DC level based on the DC level control variable resistor 65 at the time of blanking. Further, by the above-described DC component reproducing operation, the maximum potential and the DC voltage of the output signal Voo for driving the picture tube can be controlled using the cut-off adjusting variable resistor 70. The capacitors 61 and 69 are bypass capacitors for suppressing the influence of the current flowing when the switches 150 and 68 are switched to the variable resistors 65 and 70, respectively.

Next, while achieving the object of the present invention,
An embodiment capable of providing a signal processing circuit in which even when the gain of a variable gain amplifier is varied, an operating point at which the relationship between input and output signals is preserved has one point on a characteristic line indicating the relationship between input and output signals Is shown in FIG.

In FIG. 3, transistors 71 and 80
, A variable gain amplifier 110, a differential amplifier 111, an OP amplifier (or a differential amplifier) 11
2. Use of a negative feedback amplifier circuit including an inverting amplifier 113, a positive phase amplifier circuit including an OP amplifier (or differential amplifier) 78 and an emitter follower transistor 75, and a switch 114 that opens and closes based on a blanking signal source 115. And a blanking circuit.

Next, the operation of the embodiment shown in FIG. 3 will be described. An input signal to be processed is input to the base of the transistor 71. A switch 114 that opens and closes based on a blanking signal source 115 is connected to the base of the transistor 80. The switch 114 applies the output voltage value Va of the DC voltage source circuit to the base of the transistor 80 during blanking. The transistors 71 and 80 are switching circuits, and output from the emitter connection point of the transistors 71 and 80, which is the output, the base-side voltage of the transistor 80 during blanking erasure and the base-side voltage of the transistor 71 during non-blank erasing. Is done.

As a result, transistors 71 and 80
Has a waveform in which a blanking pulse is added to the input signal. The input signal to which the blanking pulse is added is AC-coupled by the capacitor 120 and is input to the variable gain amplifier 110. The drive adjustment is performed by varying the variable resistor 79, and the variable resistor 7 is controlled.
The signal amplitude of the variable gain amplifier 110 is varied based on the control voltage appearing on the slider 9. The output of the variable gain amplifier 110 is input to the inverting input of the differential amplifier 111.

In this embodiment, the differential amplifier 111 functions as an adder / subtractor. Further, the output of the differential amplifier 111 is divided by a resistor 121 and a
It is applied to the inverting input of amplifier 112. This divided voltage signal is DC-reproduced by the switch 44 which is closed at the time of erasing the negative polarity blanking, is input to the inverting amplifier 113, and is returned to the input of the variable gain amplifier 110 via a resistor, targeting the voltage value of the DC voltage source 130. . The capacitor 45 is the switch 4
Reference numeral 4 denotes a hold capacitor that holds an input signal to the inverting amplifier 113 while the switch 4 is closed.

By these means, a fixed operating point when the gain is varied can be obtained, and at the same time, the signal dynamic range of the signal processing circuit can be effectively used. Further, the switching circuit including the transistors 71 and 80 includes:
As in the present embodiment, an adder / subtractor or a differential amplifier having a blanking signal source input to one input terminal can be used instead.

[0026]

According to the present invention, there is an advantage that the input dynamic range can be effectively utilized without expanding the signal input dynamic range of the signal processing circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment for achieving the object of the present invention.

FIG. 2 is a circuit diagram showing an embodiment in which the object of the present invention has been achieved by applying the present invention to a video signal amplifier circuit.

FIG. 3 is a diagram showing an operating point in which the relationship between input and output signals is preserved even when the gain of the variable gain amplifier is changed while achieving the object of the present invention. FIG. 2 is a circuit diagram showing an embodiment capable of providing an existing signal processing circuit.

FIG. 4 is a circuit diagram showing a conventional example of a video amplifier circuit for a color CRT display.

FIG. 5 is an input / output characteristic diagram of a video amplifier circuit.

[Explanation of symbols]

110: variable gain amplifier, 4: picture tube, 100: input terminal, 101: output terminal, 201: DC component controller

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Michitaka Osawa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture, Ltd.

Claims (3)

[Claims] A first terminal for receiving an input signal;
0) and a second terminal for supplying a constant DC level (49), such as a DC level at the time of blanking, and a changeover switch (150) that switches between the second terminal and the second terminal. The terminal is connected to the first terminal, and based on a pulse signal such as a periodically generated blanking pulse, the changeover switch is connected to the second terminal for the pulse period only, thereby connecting the switch output. A changeover switch driving means (48) for outputting a signal having a fixed level DC pulse added to an input signal; and taking in a signal having a fixed level DC pulse added to the input signal, which is the changeover switch output, And a DC component controller that performs only the level control of the DC pulse and outputs the result. Signal processing circuit, characterized in that to allow effective use of the signal input dynamic range. 2. A variable gain amplifier for amplifying and outputting an input signal, a DC level source for periodically generating a DC pulse having a constant DC level such as a blanking signal, and an output of the variable gain amplifier. One of the input terminals receives a DC pulse generated at a constant period from the DC level source into the other input terminal, performs addition and subtraction between the two, and outputs the result. Ingest,
And a DC component controller that performs only the level control of the DC pulse included in the output and outputs the result.Since the level control of the DC pulse is performed, the signal input dynamic range can be effectively used. Signal processing circuit. 3. A DC level source for periodically generating a DC pulse having a fixed DC level such as a blanking signal, and an input signal is generated at one input terminal at a constant period from the DC level source. A DC pulse is input to the other input terminal, an adder / subtractor that performs addition and subtraction between the two and outputs the result, and an output of the adder / subtractor is input and only the level control of the DC pulse included in the output is performed and output. A signal processing circuit, comprising: a DC component controller for controlling a level of a DC pulse, thereby enabling an effective use of a signal input dynamic range.