JPS61192171A - Picture quality adjusting circuit - Google Patents

Abstract

PURPOSE:To obtain a flat characteristics without any corrections at the center of a volume and to secure the sufficient range of correction by performing a correction that raises a high frequency band and a correction that drops it with one picture quality adjusting volume using two variable capacitance diodes. CONSTITUTION:By moving the movable terminal of a picture quality adjusting volume 3 to the sharp side (+B side), the capacitance of the first vari-cap. diode increases and the high band of a picture signal is raised and then, a circuit that drops the high band is not operated. Conversely, by moving the movable terminal of the picture quality adjusting volume 3 to the soft side (the earth side), the capacitance of the first vari-cap. diode decreases and the circuit that raises the high band is not operated and then, the circuit that drops the high band is operated. And, when the movable terminal of the picture quality adjusting volume 3 is positioned at the center in and adjusting range, the capacitance of the first vari-cap. diode is fewer and both circuits that raise and drop the high band are not operated and so a flat frequency characteristic without any corrections is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an image quality adjustment circuit in a television receiver.

Conventional technology In general, the picture quality adjustment circuit in a television receiver is shown in Figure 2 (
As shown in Figure 2(b), a variable capacitor G is installed in parallel with a resistor in the video signal path to control the amount of increase in the high frequency of the video signal. One method was to install a variable capacitor C between the path and ground to control the amount of high frequency reduction.

Problems to be Solved by the Invention However, with these circuits, image quality adjustment can only be made in one direction, the sharp side and the soft side, so it is necessary to reversely correct the original characteristics. That is, in the circuit shown in FIG. 2(e), since the image quality adjustment is performed by increasing the high frequency range, in order to obtain a flat characteristic at the center of the adjustment range, it is necessary to perform a correction to lower the high frequency range of the input signal in advance.

For this reason, it is difficult to make both the frequency characteristics and the phase characteristics flat at the center of the adjustment range, and there is also the problem that a sufficient adjustment range cannot be obtained due to one-sided adjustment.

The present invention solves these problems, and aims to provide an image quality adjustment circuit that can easily obtain flat characteristics at the center of the adjustment range of the image quality adjustment volume and that can also have a sufficiently wide adjustment range. do.

Means for Solving the Problems The image quality adjustment circuit of the present invention uses two varicap diodes.
The present invention is characterized in that it is possible to perform both correction for increasing the high frequency range and correction for reducing the high frequency range with one image quality adjustment volume for individual use.

Operation In the circuit of the present invention, by dividing the correction on the soft side and the sharp side of the image quality adjustment volume, a flat characteristic with no correction at all can be obtained at the center of the image quality adjustment volume, and a sufficient range of correction can be obtained. be able to.

Example Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In Fig. 1, 1 is the first varicap diode to enhance the high frequency characteristics of the video signal, 2 is the second varicap diode to reduce the high frequency characteristic of the video signal, and 3 is the image quality adjustment volume. , its movable terminal is connected to the cathode of the first varicap diode 1 and to the base of the transistor 40 via a resistor.

The collector of this transistor 4 is connected to the cathode of the second varicap diode 2. Note that 6 is a video amplification transistor.

The operation of the above configuration will be explained next.

Now, set the movable terminal of the image quality adjustment volume 3 to the sharp side (
+B side), the bias on the cathode side of the first varicap diode 10 increases, and since its capacitance is large, the high frequency range of the video signal is lifted.
Transistor 4 has a raised base potential and is sufficiently conductive, so the impedance between the collector and eminog is small.
Therefore, the bias of the cathode of the varicap diode 2 is low, the capacitance is small, and the circuit for reducing high frequencies does not work.

Conversely, when the movable terminal of the image quality adjustment volume 3 is moved to the soft side (earth side), the bias of the cathode of the first varicap diode 1 becomes lower and its capacitance decreases.
The circuit that lifts the high frequencies doesn't work. On the other hand, at this time, the transistor 4 is cut off, the cathode bias of the second varicap diode 2 is sufficiently increased, the capacitance is increased, and a circuit for reducing high frequencies is activated.

When the movable terminal of the image quality adjustment volume 3 is located at the center of the adjustment range, the cathode bias of the first varicap diode 1 is the same as the DC level of the anode, the capacitance is small, and the circuit that lifts the high frequency range is not activated. It's fleeting. On the other hand, since the transistor 4 is conductive and the cathode bias of the second varicap diode 2 is low, the circuit for reducing high frequencies does not work. In other words, image quality adjustment volume 3
When the movable terminal is in the center of the adjustment range, a flat frequency response with no correction effect can be obtained.

Effects of the Invention As described above, according to the present invention, when the two parallel Yagg diodes are used and the image quality adjustment volume is moved in one direction, one of the Paris camp diodes is operated to control the video signal. By raising the high frequency range of the video signal and lowering the high frequency range of the video signal by using the other varicap diode when moving in the other direction, the adjustment range of the high frequency characteristics of the video signal can be widened. It is possible,
Furthermore, flat characteristics that are not affected by any correction can also be easily obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an image quality adjustment circuit according to an embodiment of the present invention, and FIGS. 2a and 2b are circuit diagrams of an image quality adjustment apparatus in a conventional example. 1.2...Varicap diode, 3...
...Picture quality adjustment volume, 4...Transistor.

Claims (1)

[Claims] A first varicap diode that selectively passes a high frequency portion of the video signal, a second varicap diode that attenuates the high frequency portion of the video signal, and a volume for adjusting the image quality are provided, and the image quality adjustment is performed by: An image quality adjustment circuit configured such that a first varicap diode acts when the volume is moved to one side, and a second varicap diode acts when the volume is moved to the other side.