JPH0388496A - Ghost signal generator - Google Patents

Abstract

PURPOSE:To obtain a desired ghost signal with simple constitution not requiring a long cable or the like by generating a signal retarded by a delay circuit prior to modulation into a carrier frequency. CONSTITUTION:A video signal of a base band outputted from a video signal source 11 is distributed and one of the distributed video signal is retarded at a delay circuit 13 for a prescribed time. Then both the video signals are modulated with modulators 12, 14 injected with a same carrier frequency signal and outputs of the modulators 12, 14 are added by variable attenuators 16, 18 and phase adjustment devices 17, 19 respectively. Then the added signal is frequency- converted by a mixer 21 and an oscillator 22. Thus, various states of ghost signals are generated with simple constitution not requiring a long cable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ghost signal generator suitable for use in evaluating a ghost signal removal circuit included in, for example, an HDTV system.

[Summary of the invention]

The present invention provides a ghost signal generator suitable for use in evaluating a ghost signal removal circuit included in an HDTV system, etc., in which a baseband video signal is delayed by a delay circuit, and then the delayed video signal is combined with the delayed video signal. By adding the video signals and modulating them to the carrier frequency,
This makes it possible to easily obtain a desired ghost signal.

[Conventional technology]

When receiving television broadcasts, a ghost image, in which this image is displayed superimposed on the right or left side of the original received image, often occurs. For example, as shown in Figure 3, when a broadcast signal transmitted from a television broadcast transmitting station (1) is received by an antenna (2) in each home, this ghost is reflected by other buildings (3), etc. This is also caused by the antenna (2) receiving the broadcast waves.

In recent years, various techniques for removing such ghosts have been developed. For example, in an HDTV system, it has been proposed to superimpose a reference signal for ghost removal onto a television signal. Such a ghost removal device needs to test the state of ghost removal by actually receiving a ghost signal.

FIG. 4 is a diagram showing the configuration of a conventional ghost signal generator for conducting such tests. In the figure, (4) indicates a video signal source, and the baseband video output from this video signal source is The signal is fed to a modulator (5). This modulator (
5) modulates the video signal with a carrier wave having a frequency corresponding to each transmission channel of television broadcasting.

Then, the output video signal of the modulator (5) is directly transferred to the mixer (7).
), is distributed by a distributor (6), and is supplied to an adder (7) via a coaxial cable (8) of a predetermined length and an amplifier (9). In this case, the coaxial cable (8)
For example, the length of the cable is about 100 m to 1 km, and the amplifier (9) is used to compensate for the attenuation caused by the cable of this length. Then, the adder (7) adds the respective video signals, and the added video signal is sent to the output terminal (
10).

Then, the video signal obtained at this output terminal (10) is
For example, it is supplied to a television receiver equipped with a ghost signal removal circuit.

According to this configuration, a video signal delayed for a period corresponding to the length of the coaxial cable (8) is superimposed on the original video signal at the output terminal (10), creating a pseudo ghost signal. By receiving this ghost signal, each circuit within the television receiver can be tested. Note that the ghost signal described below is a video signal in which a ghost occurs in a received image.

[Problem to be solved by the invention]

However, the conventional ghost signal generator requires a very long coaxial cable (8) in order to create the delayed signal, making the configuration of the ghost signal generator large-scale and making it difficult to detect the state in which ghosts occur. When changing, it is necessary to change the length of the coaxial cable (8), which is inconvenient and requires a lot of effort.

In reality, a 200 m cable provides a delay of about lμs, so it is difficult to prepare cables of different lengths to vary the signal delay, and it is difficult to easily change the state in which ghosts occur. I couldn't.

In view of the above, an object of the present invention is to provide a ghost signal generator that can obtain a desired ghost signal with a simple configuration.

[Means to solve the problem]

As shown in FIG. 1, for example, the ghost signal generator of the present invention distributes a baseband video signal output from a video signal source (11), and sends one of the distributed video signals to a delay circuit (13). Modulators (12), (14) into which carrier frequency signals are injected after being delayed by a predetermined time.
modulates both video signals by a modulator (12),
The output of (14) is changed to variable attenuator (16), (1B)
and are added via phase adjusters (17) and (19), respectively.

Then, this added signal is sent to the mixer (21) and the oscillator (22).
Convert the frequency by

[Effect]

According to this configuration, a signal delayed by a delay circuit is created before being modulated to the carrier frequency, so there is no need for long cables, and various ghost signals can be created by changing the settings of this delay circuit. can.

〔Example〕

Hereinafter, one embodiment of the ghost signal generator of the present invention will be described in the first embodiment.
Let me explain with reference to the diagram.

In FIG. 1, (11) indicates a video signal source that outputs a baseband video signal, and a modulator (12) and a delay circuit (13) output the baseband video signal from the video signal source (11). ) and supply to. This delay circuit (13)
is a circuit that changes the timing of a human video signal by digital processing using memory, and in this example, it changes the timing of a human video signal from 0 to 6.
The amount of delay can be changed continuously (actually, every clock of the operating clock signal) within a range of 4 μs. The output video signal of this delay circuit (13) is then supplied to a modulator (14).

Further, (15) in the figure indicates a first oscillator, and this first oscillator (15) oscillates a frequency signal of, for example, 38.9 MHz, and supplies this oscillation signal to the modulators (12) and (14). do. And these respective modulators (12) and (1
In step 4), the baseband video signal supplied from the video signal source (11) is modulated by the oscillation signal, and the oscillation signal (
38,9MHz) as an intermediate frequency signal with a carrier wave.

The intermediate frequency signal output from the modulator (12) is then supplied to the adder (20) via a variable attenuator (16) and a phase adjuster (17). Furthermore, the intermediate frequency signal output from the modulator (14) is supplied to the adder (20) via a variable attenuator (18) and a phase adjuster (19). In this case, as the phase adjusters (17) and (19), for example, a filter set with a variable capacitor and a coil is used so that the phase of the high frequency signal can be adjusted.

Then, the respective intermediate frequency signals supplied to the adder (20) are added, and the added signal is supplied to the mixer (21). In addition, (22> in the figure indicates the second oscillator, and this second oscillator
The oscillation signal of the oscillator (22) is supplied to the mixer (2I). Then, in this mixer (21), the video signal as an intermediate frequency signal supplied from the adder (20) side is frequency-converted by an oscillation signal, and the frequency is converted to a carrier wave frequency corresponding to the carrier wave of each channel of the television broadcast signal. video signal. Then, the video signal modulated by this carrier wave is
It is supplied to the output terminal (23). And the output terminal with (
The video signal of a predetermined carrier frequency obtained in step 23) is supplied to, for example, a television receiver equipped with a ghost signal removal circuit.

According to the ghost signal generator having such a configuration, various ghost signals can be generated. That is, since the amount of delay is changed with the baseband video signal, the amount of delay in the delay circuit (13) is continuously changed up to 64 μs, which is the scanning period of one horizontal line of the video signal. The ghost generation position relative to the original received image can be set at any position within one screen.

In this case, by adjusting the amount of attenuation in the attenuators (16) and (18), either a delayed ghost or an advanced ghost can be generated. That is, by setting the attenuation amount of the attenuator (18) that handles the delayed video signal to be larger than the attenuation amount of the attenuator (16), it is possible to eliminate the delayed ghost state in which a ghost occurs on the right side of the original received image. It can be a ghost signal. In addition, by setting the attenuation amount of the attenuator (16) that handles undelayed video signals to be larger than the attenuation amount of the attenuator (18), an advanced ghost state in which a ghost occurs on the left side of the original received image can be created. It can be a ghost signal.

Further, by finely adjusting the amount of attenuation of each attenuator (16) and (18), the strength of the ghost generation state can be changed. Furthermore, phase adjusters (17), (1
By adjusting 9), the hue of the ghost appearing in the displayed image can be changed. In this case, the attenuator (16),
Since the signal processing in (1B) and the phase adjusters (17) and (19) is performed by converting it into an intermediate frequency signal, good signal processing can be performed.

FIG. 2 shows a second embodiment of the present invention, in which two ghost signals can be generated.

Portions in the drawing that overlap with those in FIG. 1 are designated by the same reference numerals, and detailed explanation will be omitted.

In FIG. 2, a delay circuit (24) is added to the device in FIG.

Modulator (25), attenuator (26) and phase adjuster (27)
), a second ghost signal generating means is provided, which generates a delay amount it! ! By adjusting the delay amounts in (13) and (24), it is possible to generate two ghost signals with different delay times. Therefore, a more realistic ghost signal can be obtained.

It goes without saying that ghost signal generating means may be further provided in parallel to generate three or more ghost signals. In addition, in FIGS. 1 and 2, the phase adjuster (1
7), , (19), and (27) respectively as modulators (
12), (14), and (25).

In this way, ghost signals in various states can be generated, so that the ghost signal removal circuit can be tested under various conditions.

In this example, the delay signal is obtained by digital processing in the delay circuit, but a delay circuit that performs delay processing on the analog signal as it is may be used. However, analog delay circuits have difficulty controlling the amount of delay as finely as digital delay circuits do, and are subject to certain restrictions on the location where ghosts occur.

〔Effect of the invention〕

According to the present invention, ghost signals in various states can be generated with a simple configuration that does not require long cables, and there is an advantage that various tests can be performed based on the ghost signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of a ghost signal generator of the present invention, FIG. 2 is a block diagram showing a second embodiment of the ghost signal generator of the present invention, and FIG. 3 is a block diagram showing a ghost signal generator according to a second embodiment of the present invention. The explanatory diagram, FIG. 4, is a configuration diagram of a conventional ghost signal generator. (11) is a video signal source, (12), (14) and (
21) is a modulator, (13) is a delay circuit, (16) and (
18) is a variable attenuator, and (17) and (19) are phase adjusters. 1

Claims (1)

[Claims] 1. A baseband video signal output from a video signal source is delayed by a delay circuit, and the video signal and the delayed video signal are subjected to multiple modulations in which the same carrier frequency signal is injected. A ghost signal generator that modulates each modulator and synthesizes the outputs of these multiple modulators. 2. Delay the baseband video signal output from the video signal source by a delay circuit, modulate the delayed video signal and the undelayed video signal separately, and modulate each signal separately. A ghost signal generator that supplies a signal to an attenuator and a phase adjuster, adds the signal, modulates the summed signal, and obtains a video signal modulated to a predetermined carrier frequency.