JPH0721013Y2 - Digital television receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a digital television receiver that digitally performs signal processing such as color demodulation of a color video signal. Not only video signals (hereinafter referred to simply as composite signals),
The present invention relates to a digital television receiver capable of handling a luminance / color separation type signal (hereinafter, simply referred to as a separate signal).

(B) Conventional Technology In recent years, digital television receivers such as those described above for the purpose of improving image quality and increasing functionality have been commercialized.

The A / D converter of such a digital television receiver is generally constructed as shown in FIG. That is, the third
In the figure, (1) is an input terminal into which an analog type color composite video signal is introduced, and the composite video signal is A /
It is input to the D conversion circuit (2). This A / D conversion circuit (2)
Sends the composite video signal to the luminance / color (Y / C) separation circuit (3) after sampling and converting it into a digital signal.
At that time, the sampling clock (CK) given to the A / D conversion circuit (2) is changed to the color burst signal (BT) extracted by the burst gate circuit (4) from the output signal of the A / D conversion circuit. It is created by a PLL type sampling clock generation circuit (5) which is controlled to be synchronized. The luminance signal (Y) and the carrier color signal (C) in the digital composite signal separated from the Y / C separation circuit (3) are input to a digital signal processing system (not shown).

(C) Problems to be solved by the invention By the way, if the maximum amplitude of the analog composite signal (Fig. 4) input to the A / D conversion circuit (2) is set to 1 Vp-p, the color burst signal ( BT) is several mVp-p ~ 4
Since a fluctuation of about 00 mVp-p is considered, if the composite signal is converted to an 8-bit (256 gradation) digital signal, when the color burst signal (BT) in the composite signal is small, the burst gate circuit The digital color burst signal output from (4) is 8
It is represented only by the lower one or two bits of the bits, and becomes extremely small. As a result, this burst signal cannot be accurately detected in the PLL type sampling clock generation circuit (5), and therefore a stable sampling clock cannot be supplied to the A / D conversion circuit. Therefore, the present applicant has already proposed to provide a second A / D conversion circuit dedicated to the color burst signal in addition to the above-mentioned A / D conversion circuit (2).

On the other hand, the recent high image quality VTR (video tape recorder) called S-VHS system has an output terminal for deriving a luminance signal and a carrier color signal separately without converting a reproduced video signal into a composite signal. Accordingly, a color television receiver having a so-called S input terminal for such a separate signal has already been commercialized accordingly. Therefore, in order to digitize such a receiver, each A / D conversion circuit for the luminance signal and the carrier color signal is further required, and the above-mentioned composite signal and color burst signal are also included. Therefore, a large number of A / D conversion circuits must be used, which causes a problem that the cost is considerably increased.

Therefore, it is an object of the present invention to realize a digital television receiver that is compatible with a separate signal input at a low cost by reducing the number of required A / D conversion circuits as much as possible.

(D) Means for Solving the Problem In the digital television receiver of the present invention, the composite signal or the separate luminance signal is selectively input to the first A / D conversion circuit, and the second A / D conversion circuit is selected. In addition, the color burst signal in the composite signal or the separate carrier color signal is selectively input.

(E) Operation According to the above configuration, the first and second A / D conversion circuits are used both when the composite signal is input and when the separate signal is input, and the composite signal is generated by the two A / D conversion circuits. The separate signal is efficiently A / D converted and input to the digital video signal processing system.

(F) Embodiment FIG. 1 shows a schematic structure of a main part of an embodiment of a digital television receiver according to the present invention. In the figure, (1
1) is the input terminal of analog composite signal or separate luminance signal, these signals are the first A / D
It is inputted to the conversion circuit (12) and, on the other hand, it is inputted to the bandpass filter (13). This Band Pass Filter (13)
Is to separate and extract a carrier color signal including a color burst signal from the composite signal. The carrier color signal passes through the first burst gate circuit (14) to extract the color burst signal and perform ACC control. Circuit (15)
Entered in.

The ACC control circuit (15) controls the color burst signal so that its amplitude has a constant magnitude that substantially matches the input voltage range of the second A / D conversion circuit (17) described later, and then the first changeover switch. (16) is given to one input terminal (a). This switch (16) is for switching between composite signal input and separate signal input,
The input terminal (b) for the other carrier is connected to the input terminal (18) for the separate carrier color signal.

Therefore, when the composite signal is input when the first selector switch (16) is in the state shown in the figure, the ACC control circuit (15)
The constant amplitude color burst signal output from the second A / D
The signal is input to the conversion circuit (17), is sampled by a sampling clock (CK) described later and converted into an 8-bit digital signal, and then is passed through the second burst gate circuit (19) to obtain the PLL type synchronization circuit (20). ) Is given to.

As shown in FIG. 2, the synchronizing circuit (20) generates a clock having a frequency 4f _{5C which is} four times as high as that of the color subcarrier.
1), a timing pulse generation circuit (202) consisting of a combination of a frequency divider circuit and a logic gate that divides the oscillation output by various frequency division ratios, and a pulse of _f5C from this circuit (202). This is a well-known structure including a digital phase comparison circuit (203) for phase comparison with a digital burst signal from the second A / D conversion circuit (17) in FIG. 1 and a loop filter (204). The timing pulse generation circuit (202)
The internal frequency divider circuit is reset by the horizontal and vertical sync pulses (HP) (VP) detected by the sync signal detection circuit (21) from the output signal of the first A / D conversion circuit (12). It has become. The sampling clock (CK) from the timing pulse generation circuit (202) is the first second A /
The burst gate pulse (GP) is supplied to the D conversion circuits (12) (17) and the video / color processing circuit (23) described later.
Is supplied to the first and second burst gate circuits (14) and (19), and horizontal and vertical drive pulses (HD) (VD) are also output.

In addition, the first A / D conversion circuit (12) when the composite signal is input
Output signal is separated into a luminance signal (Y) and a carrier color signal (C) by a Y / C separation circuit (22), and the luminance signal (Y) at the time of inputting a separate signal passes through the separation circuit (22) as it is. And is input to the video / color processing circuit (23) that constitutes the digital video signal processing system (25). When the composite signal is input, the second selector switch (26) is interlocked with the first selector switch (16) and is switched to the illustrated state.
The digital burst signal from the 2A / D conversion circuit (17) is not input to the video / color processing circuit (23) and adversely affected. Further, when the separate signal is input, the first and second changeover switches (16) and (26) are switched to the states opposite to those shown in the figure, so that the carrier color signal (c) including the color burst signal input to the input terminal (18). Is A / D converted by the second A / D conversion circuit and input to the video / color processing circuit (23). Further, the color burst signal in the carrier color signal after the A / D conversion passes through the second burst gate circuit (19) and
It is supplied to the PLL synchronous circuit (20).

Here, the ACC control for the color burst signal is not performed when the separate signal is input, but the S-VHS method described above is used.
Separate carrier color signal (c) from VTR is ACC on VTR side.
Since the color burst signal in the color signal (c) is sufficiently large by being controlled, this is the 2A
When A / D converted by the / D conversion circuit (17) and supplied to the synchronization circuit (20), sampling clock (CK)
Can be accurately supplied.

Thus, the luminance and color signals (Y) and (C) at the time of inputting the composite signal and at the time of inputting the separate signal, which are input to the video / color processing circuit (23), are subjected to color demodulation in the circuit (23). Various kinds of video including a color matrix and color signal processing are digitally performed and then output as digital three primary color signals (R) (G) (B).
Then, each of these signals (R), (G), and (B) is converted into an analog signal by the D / A conversion circuit (24) and then supplied to the color output circuit.

(G) Effect of the Invention As described above, according to the present invention, it is possible to realize a digital television receiver that does not use many A / D conversion circuits and is therefore inexpensive and stable in operation and that supports separate signal input. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic structure of a main part of an embodiment of the present invention, FIG. 2 is a block diagram showing a structure of a PLL synchronizing circuit thereof, and FIG. 3 is a main part of a conventional digital television receiver. 4 is a waveform diagram of a color composite video signal. (11) …… Color composite video signal / luminance signal input terminal,
(18) …… Conveyor color signal input terminal, (12) (17) …… First
Second A / D conversion circuit, (25) …… Digital video signal processing system.

Claims (1)

[Scope of utility model registration request] 1. An analog type color composite video signal is sampled by a sampling clock synchronized with a color burst signal in the signal for A / D conversion, and the output signal is input to a digital video signal processing system to obtain a color image. In a digital television receiver adapted to display, a color burst signal separated from the color composite video signal is A / D converted and supplied to a digital PLL type synchronizing circuit for creating the sampling clock. And a switching circuit connected to the second A / D conversion circuit, and the first A / D conversion circuit for the color composite video signal is replaced with the luminance / color separation in place of the composite video signal. When the type luminance signal is input, the switching circuit inputs the separate type carrier color signal into the second A / D conversion circuit instead of the color burst signal. While, the digital television receiver, characterized in that so as to input the output signal of the first 2A / D converter to the digital video signal processing system.