JPH0544878B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a color video signal A/D conversion device for a television receiver using a panel type display section.

[Prior art and its problems] In recent years, small portable television receivers that use liquid crystal display panels in their display sections have been put into practical use.
This kind of television receiver using a conventional liquid crystal display panel converts a video signal amplified by a video amplification circuit into a digital signal by an A/D conversion circuit.
This digital signal is used to drive the liquid crystal display panel. However, due to its characteristics, the liquid crystal display panel has a narrow gradation range from the white level to the black level, making it difficult to obtain images with good contrast. In order to solve this problem, conventional methods detect the average value of the television video signal and set the reference voltage of the A/D conversion circuit accordingly to obtain good contrast. In other words, the video signal does not always change from the white level to the black level, and there is no need to A/D convert the entire range of the video signal.
As described above, contrast is improved by varying the conversion level of the A/D conversion circuit according to the video signal.

In addition, recently, liquid crystal color television receivers have been considered, and if the above-mentioned contrast control is performed in this liquid crystal color television receiver, the color video signal A/D converter is
The circuit configuration is as shown in the figure. That is, the third
In the figure, 11 is a low-pass filter in the R signal processing system 1, which is a video signal processing circuit (not shown).
The R signal shown in FIG. 4a sent from the terminal is input. This low-pass filter 11 takes out the average level of the input R signal as shown in FIG. 4b, and outputs it to level shifters 12 and 13. The level shifter 12 level-shifts the input average level to the + side as shown in FIG. 4c, and supplies it to the A/D conversion circuit 14 as an upper limit reference voltage _VH .
Further, the level shifter 13 level-shifts the input average level to the negative side as shown in FIG. 4d, and supplies it to the A/D conversion circuit 14 as a lower limit reference voltage V _L. Furthermore, this A/D conversion circuit 14
In this case, the R signal is input to the data input terminal A _IN . The A/D conversion circuit 14 converts the R signal into a 4-bit digital signal according to the upper limit reference voltage V _H and lower limit reference voltage V _L given from the level shifters 12 and 13, and converts the R signal into a 4-bit digital signal to a liquid crystal drive circuit (not shown). ).

In addition, in FIG. 3, 2 is a G signal processing system, and 3 is a G signal processing system.
is a B signal processing system, which is constructed in the same way as the R signal processing system 1 and performs the same operation.

However, when the color video signal A/D converter is configured as described above, the average values of the R, G, and B signals are detected independently, so even if the signals have the same hue, if the brightness differs, different values will be detected. There is a problem that the hue is A/D converted.

[Effects of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to provide a color video signal A/D conversion device that can reproduce a correct hue even if the average brightness of an image changes. shall be.

[Summary of the Invention] The present invention provides an A/D conversion device that A/D converts a color television video signal according to an upper limit reference voltage _VH and a lower limit reference voltage _VL .
After amplifying according to each primary color signal of B, its average value level is detected, and the upper limit reference voltage V _H and lower limit reference voltage V _L for each primary color signal are set from the average value level of this luminance signal, and each upper limit reference voltage is set. The primary color signals of R, G, and B are A/D converted in accordance with the voltage _VH and the lower limit reference voltage _VL .

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 50 is an R signal processing system, 60
70 is a G signal processing system, and 70 is a B signal processing system. In the R signal processing system 50, 51 is an amplifier, into which the luminance signal Y sent from a video signal processing circuit (not shown) is input. This amplifier 51 has a specific amplification degree for the R signal, amplifies the luminance signal Y, and outputs it to the low-pass filter 52. This low-pass filter 52 is
The average level of the input R signal is taken out and output to level shifters 53 and 54. The level shifter 53 level-shifts the input average level to the + side and inputs it to the reference voltage terminal _VrefH of the A/D conversion circuit 55 as the upper limit reference voltage VH. Further, the level shifter 54 level-shifts the input average value level to the negative side to generate a lower limit reference voltage.
Reference voltage terminal of A/D conversion circuit 55 as V _L
Enter VrefL. Furthermore, the R signal is input to the data input terminal A _IN of this A/D conversion circuit 55. The A/D conversion circuit 55 converts the R signal into a 4-bit digital signal according to the upper limit reference voltage V _H and lower limit reference voltage V _L given from the level shifters 53 and 54, and converts the R signal into a 4-bit digital signal to the liquid crystal drive circuit (not shown). ).

Further, the G signal processing system 60 includes an amplifier 61, a low-pass filter 62, level shifters 63, 64, and an A/D conversion circuit 65, similar to the R signal processing system 50. A G signal is input to the data input terminal A _IN . Further, the B signal processing system 70 also has the R signal processing system 5.
0, amplifier 71, low pass filter 7
2. Level shifter 73, 74 A/D conversion circuit 75
The B signal is input to the data input terminal A _IN of this A/D conversion circuit 75. Therefore, the above R, G, and B signals have different amplitudes, and each has a fixed ratio, that is, "R/B = 1.56",
Since it has a ratio of "G/B=0.34", the amplification factors of the amplifiers 51, 61, and 71 are set according to the ratio.

Next, the operation of the above embodiment will be explained. When the luminance signal Y shown in FIG. 2a is sent from the video signal processing circuit, this luminance signal Y is sent to the amplifiers 51 and 5.
2 and 53, respectively. That is, when the amplifier 51 in the R signal processing system 50 receives the luminance signal Y, as shown in FIG. Amplify to the same amplitude as the primary color signal). Furthermore, the amplifier 6 in the G signal processing system 60
1 amplifies the input luminance signal Y to the same amplitude as the G signal (green primary color signal), and the amplifier 71 in the B signal processing system 70 amplifies the input luminance signal Y to the same amplitude as the G signal (green primary color signal).
Amplify to the same amplitude as (blue primary color signal). However,
In the R signal processing system 50, the luminance signal output from the amplifier 51 is input to the low-pass filter 52, and its average level is determined and applied to level shifters 53 and 54 as shown in FIG. 2c. The level shifter 53 shifts the average level obtained by the low-pass filter 52 to the + side and supplies it to the A/D conversion circuit 55 as the upper limit reference voltage _VH shown in FIG. 2d. Further, the level shifter 54 is
The average value level from the low-pass filter 52 is level-shifted to the - side and the lower limit reference voltage is shown in FIG. 2e.
It is given to the A/D conversion circuit 55 as _VL . This A/D conversion circuit 55 includes level shifters 53 and 54.
The R signal _shown in _FIG . Output to

Further, in the G signal processing system 60 and the B signal processing system 70, the same operation as in the R signal processing system 50 is performed, and the upper limit reference voltage V _H and the lower limit reference voltage V are set based on the luminance signal Y, respectively. By _L
Converts the G signal and B signal into digital signals and outputs them to the liquid crystal drive circuit.

As described above, the R signal processing system 50, the G signal processing system 60, and the B signal processing system 70 generate the reference voltage V _H and the lower limit reference voltage V _L based on the luminance signal Y, and When the average value level changes, each of the R, G, and B primary color signals is subjected to similar control. Therefore, the hue of the image displayed on the liquid crystal display panel can be accurately reproduced.

[Effects of the Invention] As detailed above, according to the present invention, in a liquid crystal color television receiver, the upper limit reference voltage in each of the R, G, and B signal processing systems is determined based on the luminance signal.
Since V _H and the lower limit reference voltage V _L are set, the hue can be correctly reproduced even if the brightness signal of the image changes, and the image quality can be improved.

[Brief explanation of drawings]

1 and 2 show one embodiment of the present invention, FIG. 1 is a block diagram showing the circuit configuration, and FIG. 2 is a block diagram showing the circuit configuration.
The figure is a signal waveform diagram of each part to explain the operation, Figure 3 is a block diagram showing the circuit configuration of the A/D converter in a conventional LCD television receiver, and Figure 4 explains the operation of Figure 3. FIG. 50...R signal processing system, 51, 61, 71...
Amplifier, 52, 62, 72...Low pass filter, 53, 63, 73...Level shifter, 54,
64, 74...Level shifter, 55, 65, 75
...A/D conversion circuit, 60...G signal processing system, 7
0...B signal processing system.

Claims (1)

[Claims] 1 A/D converter for A/D converting a color television video signal according to the upper limit reference voltage V _H and lower limit reference voltage V _L
In the D conversion device, an amplifier is provided for each of the R, G, and B primary color signals and amplifies the luminance signal with a preset amplification degree corresponding to each primary color signal, and an average level of the output signal of each amplifier is provided. An average value level detection means detects each, and an upper limit reference voltage V _H and a lower limit reference voltage V _L are obtained for each primary color by level-shifting the average value level detected by this means.
R, _{G ,}
A color video signal A/D conversion device comprising an A/D conversion circuit that converts each B primary color signal into a digital signal.