JP3910332B2 - Character display circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for superimposing a character signal on a SECAM video signal, for example, a technique effective when applied to a video system.
[0002]
[Prior art]
A video system (VTR) is provided with a function for displaying characters on a screen for recording reservation or the like. Such a function is called OSD (On Screen Display). Typical video signal transmission systems include NTSC system, PAL system, and SECAM system.
[0003]
The NTSC system was recognized by the US National Television System Committee (NTSC) in 1953 and transmits Ey ', Ei', and Eq 'derived from the primary conversion from the three primary color signals of red, blue, and green. Signals are assigned bandwidths of 4, 1.5 and 0.5 MHz, respectively. The luminance signal Ey is transmitted in the same manner as in the case of the black and white television, but the two color signal components Ei ′ and Eq ′ are superimposed on the luminance signal in the form of a carrier color signal by performing quadrature two-phase modulation on the subcarrier. Is transmitted.
[0004]
The PAL system is a system developed by West Germany and is a slightly modified version of the NTSC system. The polarity of the color signal component (color difference signal) in the NTSC system is changed for each scanning line and transmitted, and the receiving side uses a one-line delay line to average the carrier color signal for two scanning lines. Thus, the subcarrier phase distortion is canceled.
[0005]
The SECAM system differs from the NTSC system and PAL system in the configuration of the carrier color signal. The two chrominance signals are line-sequentially transmitted with subcarrier frequency modulation, and are converted into simultaneous signals on the receiving side using a one-line delay line.
[0006]
An example of a document describing a video signal transmission method is “Electronic Communication Handbook (starting from page 1555)” issued by Ohm Co., Ltd. on August 20, 1983.
[0007]
[Problems to be solved by the invention]
As described above, since the SECAM method is a unique transmission method compared to the NTSC method and the PAL method, when the OSD display is enabled, the NTSC method or the PAL method circuit cannot be used. It is necessary to provide a dedicated circuit for the SECAM system. According to the study of the present inventor, in the NTSC system and the PAL system, white, black or gray OSD display is possible only by switching DC (direct current) without an oscillator, whereas the SECAM system. In OSD display, since it is necessary to alternately add two types of frequencies for each line, two types of oscillation circuits are required to realize this, and the circuit scale is considered to increase.
[0008]
In addition, since two signals are alternately transmitted by switching the switch, a high frequency component deviating from the frequency band of the SECAM method is generated at the moment of switching, which becomes noise in OSD character display.
[0009]
An object of the present invention is to simplify a character display circuit in the SECAM system. Another object of the present invention is to reduce noise in SECAM OSD character display.
[0010]
The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.
[0011]
[Means for Solving the Problems]
The following is a brief description of an outline of typical inventions disclosed in the present application.
[0012]
That is, a first resistor for capturing a SECAM video signal, a second resistor coupled to the first resistor, a voltage source for outputting a DC voltage, and a voltage source corresponding to the input SECAM character signal. And a switch circuit for superimposing the output voltage on the SECAM video signal through the second resistor.
[0013]
According to the above means, the switch superimposes the output voltage of the voltage source on the SECAM video signal via the second resistor in accordance with the SECAM character signal. According to this signal superimposition, a luminance difference from the background image can be given to the character portion, thereby achieving the visualization of the character. In order to superimpose the output voltage of the voltage source on the video signal of the SECAM system via the second resistor, two types of oscillation circuits compatible with the SECAM system and their peripheral circuits are unnecessary, which is a simple circuit. To achieve Further, since the output signals of the two types of oscillation circuits corresponding to the SECAM method are not transmitted alternately, a high frequency component deviating from the frequency band of the SECAM video signal is present at the moment of switching the output signals of the two types of oscillation circuits. Can be avoided, which achieves noise reduction.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 14 shows a video system to which the current output circuit according to the present invention is applied.
[0015]
The video system 140 shown in FIG. 14 is not particularly limited, but a tuner 141 for receiving radio waves from a broadcasting station, a video signal from the tuner 141 or a video signal input from an external input terminal to the cassette tape 151. A recording block 142 for recording, a mechanism block 143 for recording a signal on the cassette tape 151 and a read-out of the recording signal, and a video signal read from the cassette tape 151 are reproduced to an AV (audio / visual) monitor. A reproduction block 145 for outputting, a power supply block 146 for supplying operation power for each unit, and a system control block 144 for controlling the overall operation are included.
[0016]
The mechanism block 143 includes a video head for magnetic recording to and reading from the cassette tape 151, a servo IC (semiconductor integrated circuit) for running the cassette tape 151, a control microcomputer, and the like.
[0017]
The reproduction block 145 includes a luminance signal system 153 for processing a luminance signal read from the cassette tape 151, a color signal system 154 for processing a color signal, a combining circuit 155 for combining these output signals, and this combining circuit. A selection circuit 156 for selecting an output signal of 155 and an output signal of the upper recording block 145, a character addition unit 130 for adding character information to the selection output signal of the selection circuit 156, and the output signal are externally output. Output amplifier 157.
[0018]
FIG. 13 shows a configuration example of the character adding unit 130.
[0019]
The character adding unit 130 is not particularly limited, but is formed on one semiconductor substrate such as a single crystal silicon substrate by a known semiconductor integrated circuit manufacturing technique.
[0020]
The video signal input from the input terminal CVideoIN is input to the SECAM system OSD character display circuit 10 through the buffer amplifier 138, where character addition based on the SECAM system character signal 61 is performed and then the buffer amplifier 139. Output from the output terminal CVideoOUT.
[0021]
A synchronization separation circuit 133 for generating a vertical synchronization signal Vsync and a horizontal synchronization signal Hsync based on the output signal of the buffer amplifier 138 is provided. The horizontal synchronization signal Hsync is stabilized by a PLL (phase locked loop) circuit 137 at the subsequent stage. The stabilized horizontal synchronization signal HsyncPLL is input to the control circuit 76 and the dot clock generation circuit 134. The dot clock generation circuit 134 generates a dot clock signal in synchronization with the input horizontal synchronization signal HsyncPLL. This dot clock signal is transmitted to the control circuit 132. A display data RAM (random access memory) 135 for storing display data and a character data ROM (read only memory) 136 for storing character data are provided, and are controlled by the control circuit 132. The SECAM character signal 61 read from the character data ROM is input to the SECAM OSD character display circuit 10.
[0022]
FIG. 1 shows a configuration example of a SECAM OSD character display circuit 10.
[0023]
The SECAM OSD character display circuit 10 is coupled to a resistor 11 that couples the output terminal of the buffer amplifier 138 and the input terminal of the buffer amplifier 139 and a terminal (referred to as “node 13”) of the resistor 11 on the buffer amplifier 139 side. A resistor 12, a voltage source 10, and a switch circuit 14 for supplying the output voltage Vo of the voltage source 10 to the resistor 12 based on the SECAM character signal 61. The output voltage Vo of the voltage source 10 is intermittently supplied to the resistor 12 based on the SECAM character signal 61, so that the SECAM video signal (composite video signal) input through the buffer amplifier 138 An OSD character having the same color as the signal and a luminance different from that of the video signal is superimposed. That is, when the SECAM character is displayed, the switch circuit 14 is turned on by the SECAM character signal 61, so that the DC voltage to the node 13 is obtained using the resistance ratio of the resistors 11 and 12 and the output voltage Vo of the voltage source 15. By performing the addition, amplitude modulation of the video signal is performed. Since the level of the voltage represents the brightness, that is, the brightness of the character, the OSD character part is displayed with a brightness different from that of the background. Characters are visualized by the brightness difference.
[0024]
FIG. 2 shows a configuration example of the switch circuit 14.
[0025]
As shown in FIG. 2, the switch circuit 14 is not particularly limited, but a p-channel type MOS transistor 21 and an n-channel type MOS transistor 22 are connected in parallel, and the logic of the SECAM character signal 61 is inverted to the p-channel type. And an inverter 23 for supplying the gate electrode of the MOS transistor 21. When the SECAM character signal 61 is at a high level, the output terminal of the voltage source 15 is coupled to the resistor 12 by turning on both the p-channel MOS transistor 21 and the n-channel MOS transistor 22.
[0026]
The voltage source 15 is not particularly limited, but a voltage source 15 in which two resistors 31 and 32 are connected in series as shown in FIG. 3 can be applied. One end of the resistor 31 is coupled to the high potential side power source Vdd, and one end of the resistor 32 is coupled to the low potential side power source Vss. Then, an output terminal of a voltage Vo of a predetermined level determined by the resistance ratio thereof is drawn out from a series connection node of the two resistors 31 and 32.
[0027]
FIG. 6 shows a circuit to be compared with the SECAM OSD character display circuit 10 shown in FIG.
[0028]
The SECAM system OSD character display circuit 60 shown in FIG. 6 includes a first oscillation circuit 63 for generating a 4.25 MHz signal, a second oscillation circuit 64 for generating a 4.40625 MHz signal, and line switching. A switch circuit 68 for selecting an output signal of the first oscillation circuit 63 and an output signal of the second oscillation circuit 64 according to the signal 62, a coupling capacitor 66, a voltage source 67, and an ON / OFF according to the SECAM character signal 61. A switch circuit 65 to be controlled. The output signal of the first oscillator 63 and the output signal of the second oscillator 64 are transmitted to the switch circuit 65 through the coupling capacitor 66. At this time, the output signal of the first oscillator 63 and the output signal of the second oscillator 64 are superimposed on the output DC voltage of the voltage source 67. That is, in the SECAM system, there are a first oscillation circuit 63 and a second oscillation circuit 64 as oscillation circuits having two center frequencies. When the switch circuit 68 is switched under the control of the line switching signal 62, the input SECAM is performed. The same center frequency as that of the video signal is selected by the switch circuit 68, and is superposed on the DC voltage of the voltage source 67 through the coupling capacitor 66.
[0029]
FIG. 4 shows, as a display example in the SECAM method, a TV (television) screen 41 with a red apple on a yellow plate on a blue background, and a SECAM video signal 42 for constructing such a screen. Is shown. In the SECAM video signal (composite video signal), the hue is determined by the frequency modulation degree from the center frequency, and the luminance, that is, the brightness of the color is determined by the DC voltage. In order to add the OSD character, the background signal is switched to the oscillation circuit output signal by the SECAM character signal 61. For this reason, since the character signal has the same frequency as the center frequency, it is displayed as a white, black, or gray OSD character on the TV display screen.
[0030]
In the NTSC system and PAL system, white, black, or gray OSD display can be displayed only by switching the DC voltage, whereas in the SECAM system, two types of frequencies need to be added alternately for each line. Therefore, as shown in FIG. 6, two types of oscillators 63 and 64 dedicated to the SECAM method are required, and the circuit scale increases accordingly. Further, since the two signals are alternately transmitted by the switching of the switch circuit 68, a high frequency component deviating from the frequency band of the SECAM video signal is generated at the moment of switching, and appears as noise in the OSD character. For example, as shown in FIG. 5, the signal at the moment of switching by the background video signal SECAM character signal 61 is a high frequency component 52 outside the frequency band of the SECAM video band signal. Since the high-frequency component is not a normal video signal, noise 53 is generated at the boundary between the background on the video and the OSD character.
[0031]
On the other hand, in the SECAM system OSD character display circuit 10 shown in FIG. 1, the DC voltage Vo is added to the video signal by performing on / off control of the switch circuit 14 according to the input SECAM character signal 61. Since the amplitude is modulated, a luminance difference from the background image can be given to the OSD character portion, and the OSD character is visualized thereby. Therefore, the first oscillation circuit 63 and the second oscillation circuit 64 shown in FIG. , The switch circuit 68 and the coupling capacitor 66 are not required, thereby greatly simplifying the circuit configuration. Further, in the circuit configuration shown in FIG. 6, since the two signals are alternately transmitted by switching the switch circuit 68, a high frequency component deviating from the frequency band of the SECAM video signal is generated at the moment of switching, and this is generated by the OSD character. However, in the circuit configuration shown in FIG. 1, since the two signals are alternately transmitted by switching the switch circuit 68, a high frequency component deviating from the frequency band of the SECAM video signal at the moment of switching is present. Therefore, no noise is generated due to the switching of the switch, so that a good OSD character display is possible.
[0032]
According to the above example, the following effects can be obtained.
[0033]
(1) Since the switch circuit 14 is turned on / off in accordance with the input SECAM character signal 61, and the amplitude modulation is performed by adding the DC voltage Vo to the video signal, the luminance difference between the OSD character portion and the background image Since the OSD characters are visualized, the first oscillation circuit 63, the second oscillation circuit 64, the switch circuit 68, and the coupling capacitor 66 shown in FIG. The circuit configuration is greatly simplified.
[0034]
(2) Since the area occupied by the chip of the SECAM system OSD character display circuit 10 can be reduced by the effect of the above (1), the SECAM system OSD character display circuit 10 can be provided at low cost. The cost of a semiconductor integrated circuit such as a microcomputer to be mounted can be reduced.
[0035]
(3) The SECAM system OSD character display circuit 10 is not a system in which two signals are alternately transmitted by switching the switch circuit 68, and a high frequency component deviating from the frequency band of the SECAM video signal may be generated at the moment of switching. Therefore, generation of noise due to switch switching can be avoided, and good OSD character display becomes possible.
[0036]
Next, another configuration example of the SECAM OSD character display circuit will be described.
[0037]
The SECAM system OSD character display circuit 10 shown in FIG. 7 is different from that shown in FIG. 1 in that a cursor or border display circuit 72 is provided.
[0038]
According to the cursor or border display circuit 72, for example, when an OSD character having a higher brightness than the background video signal is displayed, a cursor or border having a lower brightness than the background video signal is added around the OSD character. Can do. In the cursor or border display circuit 72, a resistor 73 connected to the voltage source 75 via a switch circuit 74 controlled by the cursor or border signal 71 is a node at the same position as the SECAM OSD character display circuit 10 described above. 13 is connected. The cursor or border is displayed by turning on the switch 74 and performing DC addition to the input signal and amplitude modulation of the input signal using the resistance ratio of the resistor 11 and the resistor 73 and the voltage of the voltage source 75. It is possible. For example, a cursor or border having a brightness lower than that of the background can be added before and after the OSD character having a brightness higher than that of the background.
[0039]
FIG. 8 shows a display example when the SECAM system OSD character display circuit 10 shown in FIG. 7 is adopted and various signals, that is, A in the screen when the OSD character “I” with a border is displayed on the TV screen 81. A relationship among the SECAM video signal (composite video signal) 82, the SECAM character signal 61, and the SECAM border signal 71 corresponding to -A 'is shown.
[0040]
By switching between the SECAM character signal 61 and the SECAM border signal 71, the brightness of the input video signal is raised and lowered and output as the SECAM video signal 82, so that the contrast between the character and the background can be enhanced. There is an advantage that characters can be displayed more clearly.
[0041]
The SECAM OSD character display circuit 10 shown in FIG. 9 is different from the circuit shown in FIG. 7 in that a resistor 93 is provided. The resistor 93 is provided between the node 13 and the buffer amplifier 139. When the terminal of the resistor 93 on the buffer amplifier 139 side is a node 94, a cursor or border display circuit 72 is connected to the node 94. In this manner, by interposing the resistor 93 between the SECAM character display system and the cursor or border display system, it is possible to prevent both of the buffers. When the resistor 93 is provided, an undesired current flows between the SECAM character display system and the cursor or border display system at the moment when the SECAM character and the cursor or border display are switched by the switch circuits 14 and 74. It is possible to alleviate noise superimposed on the video signal.
[0042]
The SECAM-type OSD character display circuit 10 shown in FIG. 10 is different from the circuit shown in FIG. 1 in that a capacitor 101 is connected between a connection node between the switch circuit 14 and the resistor 12 and the low-potential-side power supply Vss. This is the point. While the switch circuit 14 is off, the capacitor 101 is charged by the SECAM video signal. When the switch 14 is turned on, the output voltage of the voltage source 15 is transmitted to the capacitor 104, and the capacitor 104 is recharged by the output voltage. Therefore, the switching of the switch circuit 14 is performed only during the period necessary for this recharging. The video signal waveform at the time becomes dull. From this, the high frequency component accompanying the switching of the switch circuit 14 is reduced, so that it is possible to reduce noise when the switch circuit 14 is switched.
[0043]
The SECAM OSD character display circuit 10 shown in FIG. 11 is different from the circuit shown in FIG. 1 in that a capacitor 111 is provided. The capacitor 11 functions as a high-pass filter by being connected in parallel to the resistor 11 on the video signal input side. That is, by providing the capacitor 111, a gain decrease due to the resistor 11 can be prevented. Similarly to the circuit shown in FIG. 10, since the signal waveform can be blunted using the time required for charging the capacitor 111, noise can be reduced.
[0044]
The SECAM OSD character display circuit 10 shown in FIG. 12 is different from the circuit shown in FIG. 11 in that a resistor 121 is provided between the resistor 12 and the capacitor 111 and the node 13. This resistor 121 reduces current leakage between the SECAM character display system and the cursor or border display system, similar to the resistor 93 in the circuit shown in FIG.
[0045]
Although the invention made by the present inventor has been specifically described above, the present invention is not limited thereto, and it goes without saying that various changes can be made without departing from the scope of the invention.
[0046]
For example, in FIGS. 1, 7, 9, 11, and 12, the arrangement locations of the resistor 12 and the switch circuit 14 are interchangeable. In FIGS. 7 and 9, the arrangement locations of the resistor 73 and the switch circuit 74 are interchangeable. Further, in the above example, the resistors 11, 12, 73, 93 and 121 share the source and drain of the p-channel MOS transistor and the n-channel MOS transistor in addition to the diffusion layer and the resistance element such as polycrystalline silicon. Or only a p-channel MOS transistor or an n-channel MOS transistor. In that case, a high-potential-side power supply voltage, a low-potential-side power supply voltage, or an appropriate bias voltage can be supplied to the gate electrode of the MOS transistor. The capacitors 101 and 111 can be formed by an oxide film capacitor between the gate and the substrate of an n-channel MOS transistor or a p-channel MOS transistor, or another interlayer film capacitor.
[0047]
In the above description, the case where the invention made mainly by the present inventor is applied to the video system which is the field of use as the background has been described. However, the present invention is not limited to this and is also applied to a television receiver. can do.
[0048]
The present invention can be applied on condition that at least a SECAM video signal is handled.
[0049]
【The invention's effect】
The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
[0050]
In other words, by superimposing the output voltage of the voltage source on the SECAM video signal via the second resistor by the operation of the switch according to the SECAM character signal, a luminance difference from the background image can be given to the character portion. , Thereby achieving character visualization. In order to superimpose the output voltage of the voltage source on the SECAM video signal via the second resistor in accordance with the SECAM character signal, two types of oscillation circuits compatible with the SECAM method and their peripheral circuits are unnecessary. Can be simplified. Further, since the output signals of the two types of oscillation circuits corresponding to the SECAM method are not transmitted alternately, a high frequency component deviating from the frequency band of the SECAM video signal is present at the moment of switching the output signals of the two types of oscillation circuits. Occurrence can be avoided, and noise can be reduced accordingly.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a configuration example of a SECAM OSD character display circuit which is a configuration example of a character display circuit according to the present invention.
FIG. 2 is a circuit diagram illustrating a configuration example of a switch circuit in the SECAM OSD character display circuit.
FIG. 3 is a circuit diagram of a configuration example of a voltage source in the SECAM OSD character display circuit.
FIG. 4 is an explanatory diagram of a video signal and a display example in the SECAM system.
FIG. 5 is an explanatory diagram of noise generation when a circuit to be compared with the OSD character display circuit is employed.
FIG. 6 is a circuit diagram of a configuration example of a circuit to be compared with the OSD character display circuit.
FIG. 7 is a circuit diagram showing another configuration example of the OSD character display circuit.
8 is an explanatory diagram of a display example when the circuit shown in FIG. 7 is employed.
FIG. 9 is a circuit diagram showing another configuration example of the OSD character display circuit.
FIG. 10 is a circuit diagram showing another configuration example of the OSD character display circuit.
FIG. 11 is a circuit diagram showing another configuration example of the OSD character display circuit.
FIG. 12 is a circuit diagram showing another configuration example of the OSD character display circuit.
FIG. 13 is a block diagram illustrating a configuration example of a character addition unit including the OSD character display circuit.
FIG. 14 is a block diagram illustrating a configuration example of a video system including the character addition unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 SECAM system OSD character display circuit 11, 12 Resistance 14 Switch circuit 15 Voltage source 61 SECAM character signal 130 Character addition part 132 Control circuit 133 Synchronization separation circuit 134 Dot clock generation circuit 135 Display data RAM
136 Character data ROM
137 PLL circuit 138, 139 Buffer amplifier

Claims (3)

A character display circuit for enabling character display by superimposing a character signal on a SECAM video signal,
An input buffer for receiving the SECAM video signal;
A first resistor having one end coupled to the output terminal of the input buffer ;
A first voltage source for outputting a first DC voltage;
Receiving the first DC voltage at one end, a first switch circuit for outputting a voltage is selectively and responds to SECAM character signal,
A second resistor having one end coupled to the other end of the first switch circuit;
A third end is coupled to the other end of the second resistor and the other end is coupled to the other end of the first resistor to apply a first voltage based on the first DC voltage to the other end of the first resistor. Resistance,
An output buffer having an input terminal coupled to the other end of the first resistor;
A capacitive element coupled between a coupling point of the second resistor and the third resistor and one end of the first resistor;
A second voltage source for outputting a second DC voltage;
A second switch circuit that receives the second DC voltage at one end and selectively outputs a voltage in response to an edge signal;
One end is coupled to the other end of the second switch circuit, the other end is coupled to the other end of the first resistor, and a second voltage lower than the first voltage is applied to the first resistor based on the second DC voltage. A fourth resistor applied to the other end ,
The first voltage by adding character display data in the video signal by superimposing the video signal of the SECAM system, that you added a small border data luminance than the character display data around the character display data Character display circuit. In claim 1,
The first voltage is a character, characterized in that the resistance ratio between the combined resistance and the first resistor and the second resistor on SL and the third resistor, a voltage based on the above-described first DC voltage Display circuit. In claim 1 or 2 ,
It said second voltage is a character display circuit, characterized in that the resistance ratio between the upper Symbol first resistor and said fourth resistor, a voltage based on the said second DC voltage.

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