JPS6271390A - Intermediate-level setting circuit for video - Google Patents

Abstract

PURPOSE:To convert an analog video signal to a digital one with an excellent balance by varying the intermediate-level setting voltage of an A/D converter to process a video signal associatively with at least either black-level setting voltage or white-level setting voltage. CONSTITUTION:The white-level voltage is obtained by voltage-dividing the power source voltage Vcc by resistors R4 and R5. The intermediate level voltage and the black-level voltage are respectively obtained by voltage-dividing the power source voltage Vcc by resistors R1, R2 and R3 when a black-level setting circuit 1 is not operating. When the circuit 1 operates and the black-level setting voltage goes to VL, the setting voltage of intermediate level also varies goes to VL, the setting voltage of intermediate level also varies associatively from VM to V'M, and the video signal can be converted to a digital signal with excel lent balance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video intermediate level setting circuit for a video portion when converting an analog video signal to digital.

Conventional technology When converting an analog video signal to digital, it is necessary to set the black level voltage and white level voltage of the video signal. If you want to have sex,
In addition to the black level voltage and the white level standard voltage, an intermediate level voltage may be set. These three voltage levels are
Generally, it is fixed, but in order to efficiently convert an analog video signal to digital, the set voltage of the black level or white level is sometimes made adjustable and the set voltage is changed.

An example of the conventional level setting described above will be described below with reference to the drawings.

3A and 3B show conventional level setting circuits.

FIGS. 4 and 5 each show the operation of setting each level for a video signal.

In Figure 3A, transistors Q1 and Q2゜Q3 and 0
4. Q5 and Q6 are for supplying a white level setting voltage, an intermediate level setting voltage, and a black level setting voltage to the A/D converter IC1 at low impedance, respectively. The black level setting circuit 1 changes the black level setting voltage, and this means can be achieved, for example, by the circuit shown in FIG. 3B. That is, by changing the variable resistor VR1 in FIG. 3B, the set voltage can be variably adjusted.

Now, when the black level setting circuit 1 is not working, that is, when the diode D1 is not conducting in the circuit of FIG. 3B, the white level voltage and intermediate level voltage in FIG. 3A are set by the resistor R4, Power supply voltage ■ by R12 and R13. Similarly, the black level voltage is obtained by dividing the power supply voltage Vcc by resistors R11 and R3. This can be schematically illustrated as shown in FIG. In Figure 4,
VL, VM, and VH are black level voltages, respectively;
Indicates intermediate level voltage and white level voltage. On the other hand, A
The digital video signal output of the /D converter becomes a polygonal line as shown in FIG.

Next, when the black level setting circuit is adjusted for the video signal as shown in FIG. 6 and the black level setting voltage becomes ■L', the gradation of the digital video signal output with respect to the voltage level becomes It will look like the solid line in the figure.

Problems to be Solved by the Invention In such conventional circuits, the setting voltages for the intermediate level and white level are fixed, so the gradation of the digital video signal output of the video signal from the black level to the intermediate level is increased. However, the gradation of the digital video signal output from the intermediate level to the white level does not change and becomes extremely unbalanced.

The present invention attempts to eliminate this imbalance.

Means for Solving the Problems In order to solve the above problems, the present invention obtains an intermediate level voltage from a point that moves with changes in at least one of the black level voltage and the white level voltage. be.

According to the present invention, with the above-described configuration, the intermediate level voltage changes in accordance with a change in at least one of the black level voltage and the white level voltage, so that analog video signals can be converted into digital signals in a well-balanced manner.

Embodiment FIG. 1 shows an embodiment of the video intermediate level setting circuit of the present invention. In FIG. 1, the white level voltage is resistor R4,
The intermediate level voltage, black level voltage, is obtained by dividing the power supply voltage vcC by Rts, and when the black level setting circuit 1 is not working, the voltage CC is divided by the resistor R1,
They can be obtained by dividing the pressure in R2 and R3. Now, when the black level setting circuit 1 in FIG. 1 operates and the black level setting voltage becomes ■L' in FIG. 5, the intermediate level setting voltage also changes from VM to vM'.
Video signals can be digitally converted in a well-balanced manner. Note that the above operation can be considered in the same way when the white level setting voltage is changed.

FIG. 2 shows an embodiment of the video intermediate level setting circuit of the present invention. In FIG. 2, compared to FIG. 1, the power supply for the intermediate level and black level voltages is moved from the power supply voltage vcc to the white level voltage, and a white level setting circuit 2 is added. In this configuration, when the white level setting circuit 2 is fixed and the black level setting circuit 1 is adjusted to change the black level setting voltage, for example, as the black level setting voltage increases, the intermediate level setting voltage also increases. Depending on this change, the flavor becomes better. Also, if the black level setting circuit 1 is fixed and the white level setting circuit 2 is adjusted to change the white level setting voltage, for example, if the white level setting voltage becomes lower, the intermediate level setting voltage will also change according to this change. Effects of the Three Inventions that Reduce the Effects As described above, according to the present invention, a video signal can be digitally converted in a well-balanced manner, and is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of the video intermediate level setting circuit of the present invention, FIG. 2 is a circuit diagram of another embodiment of the video intermediate level setting circuit of the present invention, and FIG. 3A is a circuit diagram of a conventional video intermediate level setting circuit. FIG. 3 is a circuit diagram of a level setting circuit, and FIG. 3 is a circuit diagram of a black level setting circuit in the same circuit. FIGS. 4 and 5 are diagrams showing the operation of each level setting for a video signal, respectively. 1...Black level setting circuit, 2...White level setting circuit, IC1...A/D converter. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure IC/ Figure 2 Figure 3 (β) Figure 4 Gradation time Figure 5 Procedure amendment (method) % formula % 2 Name of the invention Video intermediate level setting circuit 3 Person who makes the correction A'1 Related Patent Application Person Address 1006 Oaza Kadoma, Kadoma City, Osaka Name (582) Representative of Matsushita Electric Industrial Co., Ltd.
Akira Tanii, Agent for 1FF4 Address: 7, Matsushita Electric Industrial Co., Ltd., 1006 Kadoma, Kadoma City, Monjo City, Osaka Prefecture, 571 Prefecture. Figure 3B is corrected to ``.

Claims (1)

[Claims] A video intermediate level setting circuit characterized in that the intermediate level setting voltage of an A/D converter that processes a video signal is changed together with at least one of a black level setting voltage and a white level setting voltage.