JPH01128678A - Picture quality adjusting circuit - Google Patents

Abstract

PURPOSE:To reduce the number of parts and to adjust the frequency characteristics of a picture quality adjusting circuit by using an active all pass type filter, which can change a group delay characteristics, instead of a delay line. CONSTITUTION:In the title device, the active all pass type filter is used instead of the delay line. Namely, active all pass type filters 7 and 8 previously set the frequency characteristics, and as a result, either change the frequency characteristics of the picture quality adjusting circuit or change the frequency characteristics of the picture quality adjusting circuit by changing the group delay characteristics with a delaying time control circuit 9, based on the fixed group delay characteristics corresponding to the frequency characteristics. Thus, a cost can be reduced, and the frequency characteristics can be adjusted.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is directed to a television receiver (hereinafter referred to as TV).
The present invention relates to an image quality adjustment circuit belonging to a video signal processing circuit used in a video tape recorder (hereinafter referred to as a VTR).

[Conventional technology]

Figure 3 shows, for example, Electronics Life (1982, 2)
This is a configuration diagram of a conventional image quality adjustment circuit shown in
In the figure, 1 is a first delay line that delays the video signal input from the input cover terminal Tl by a delay time ΔT, 2 is a second delay line that delays the output of the first delay line 1 by ΔT, and 3 is A A mixer that attenuates the output level to A after adding the video signal of the point and the output signal of the second delay line 2; 4 is a mixer that subtracts the output signal of the mixer 3 from the output signal of the first delay line 1; 5 is mixer 4
An attenuator 6 controls the level of the output signal of the first delay line 1, and a mixer 6 adds the output signal of the first delay line 1 and the output signal of the attenuator 5.

T2 is an output terminal.

Next, the operation will be explained. Figures 4(a) to 4(f)
) is a time chart showing signal waveforms at points A to F in FIG. First, the input terminal TI shown in FIG.
) is input to the first delay line 1.

The output signal of the first delay line 1 becomes the signal at point B shown in FIG. It is.

This signal at point B passes through the second delay line 2, and a signal with a delay time ΔT unique to the second delay line becomes the signal at point 0 as shown in FIG. 4(C). is output.

The signal at point 0 and the video signal at point A input from the input terminal T1 are mixed by the mixer 3 at the first point. The video signal passing through the second two delay lines 1.2 and the input video signal are added, and the signal converted to % is output as a signal at point D shown in FIG. 4(d).

Then, by mixer 4, the output signal of mixer 3 is subtracted from the output signal of first delay line 1, as shown in FIG.
) is output.

The output signal of the mixer 4 shown in FIG. 4(e) is level-controlled by an attenuator 5. The output signal of the level-controlled attenuator 5 and the first delay line 1
. . are added by the mixer 6, and the signal at point F shown in FIG.

Note that the image quality adjustment is performed by changing the output level amount of the attenuator 5.

[Problem that the invention seeks to solve]

Conventional image quality adjustment circuits are configured as described above, so they have problems such as having to use an expensive delay line and making it difficult to adjust the frequency characteristics of the image quality adjustment circuit. there were.

The present invention has been made to solve the above-mentioned problems, and aims to provide an image quality adjustment circuit that can reduce costs and adjust frequency characteristics.

[Means for solving problems]

The image quality adjustment circuit according to the present invention uses an active all-bus filter instead of a delay line.

[For production]

The active all-bus filter in this invention is
Set the frequency characteristics in advance and change the frequency characteristics of the image quality adjustment circuit based on the corresponding fixed group delay characteristics, or change the group delay characteristics using the delay time control circuit to adjust the image quality. Change the frequency characteristics of the adjustment circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 7 is an active all-bus filter, 8
are the second active all-bus type filters, and are respectively similar to the first active filter in FIG. It is connected to the second delay line 1.2.

Reference numeral 9 denotes a delay time control circuit, which changes the group delay characteristics of the first and second active all-bus filters 7.8.

A mixer 3 attenuates the output level to 2 after adding the video signal input to the input terminal TI and the output signal of the second active all-bus filter 8.

4 is a mixer that subtracts the output signal of mixer 3 from the output signal of the first active all-bus filter; 5 is an attenuator that controls the level of the output signal of mixer 4;
A mixer 6 adds the output signal of the first active all-bus filter 1 and the output signal of the level controller 5, and outputs the output signal to the output terminal T2.

Next, the operation will be described using the time chart shown in FIG. 2. These figures 2(a) to 2(f) are from point a in figure 1 to
As shown in FIG. 2(a), the video signal at point a input to the input terminal T1 is supplied to the first permanent all-pass filter 7 and the mixer 3. be done. The group delay characteristic of the first active all-pass type filter 7 is changed by the delay time control circuit 9 and can be freely adjusted to have a desired characteristic.

Therefore, at point b, the output of the first active all-pass filter becomes a signal having a delay time Δm adjusted by the delay time control circuit 9 with respect to the input signal, as shown in FIG. A second active all-pass filter 8 and a mixer 4.6 are fed.

The second active all-pass filter 8 is the same as the first active all-pass filter 7, and is shown in FIG.
The output at the 0 point shown in C) becomes a signal having a delay time of Δt with respect to the output signal of the first active all-pass filter, and is supplied to the mixer 3.

The mixer 3 adds the input signal at point a and the output signal of the second active all-pass filter 8 at point 0, and then
As shown in the figure (b), at point d, a signal attenuated to % is output and supplied to the mixer 4.

Mixer 4 outputs a signal obtained by subtracting the output signal of mixer 3 (point d) from the output signal of the first active all-pass filter (point b) to point e as shown in FIG. 2(e). , is supplied to an attenuator 5 for level control.

The signal whose level has been freely controlled by the attenuator 5 is supplied to the mixer 6. The mixer 6 adds the output signal of the first active all-pass filter (point b) and the output signal of the level-controlled attenuator 5, and outputs the output signal at the point f as shown in FIG. 2(f). Output terminal T2
supply to. - In the above embodiment, the delay time control circuit 9 is provided so that the frequency characteristics of the image quality adjustment circuit can be adjusted, but the desired frequency characteristics of the image quality adjustment circuit can be set in advance, and the corresponding fixed group delay Only active all-pass filters with specific characteristics may be used.

〔Effect of the invention〕

As described above, according to the present invention, an active all-pass filter that can change the group delay characteristic is used instead of a delay line, making it ideal for IC implementation, reducing the number of parts and cost, and This has the advantage that the frequency characteristics of the image quality adjustment circuit can be adjusted.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an image quality adjustment circuit according to an embodiment of the present invention, FIG. 2 is a time chart showing waveforms at each point in the same embodiment, and FIG. 3 is a circuit configuration diagram showing a conventional image quality adjustment circuit. , FIG. 4 is a time chart showing waveforms at each point in FIG. 3-6 Mixer, 5 Attenuator, 7 First active all-pass filter, 8 Second active all-pass filter, 9 Delay time control circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A first active all-pass filter that has a group delay characteristic that delays the video signal input to the input terminal, and a second active filter that has a group delay characteristic that delays the output of the first active all-pass filter. an all-pass filter; a first mixer that adds the video signal input to the input terminal and the output signal of the second active all-pass filter; and attenuates the added signal; a second mixer that subtracts the output signal of the first mixer from the output signal of the active all-pass filter; a level control circuit that controls the level of the output signal of the second mixer; and a third mixer that adds the output signal of the active all-pass filter and the output signal of the level control circuit and outputs the result to an output terminal. (2) The image quality adjustment circuit according to claim 1, wherein group delay characteristics of the first and second active all-pass filters are changed by a delay control circuit.