JPS5842996B2 - Ghost removal circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ghost removal circuit that can cancel reception interference caused by ghost waves in a television receiver when receiving television broadcasting.

In general, ghost waves are generated when reflected waves or diffracted waves from topographical features such as mountains or buildings such as buildings during the propagation of the broadcast wave desired to be received, that is, a direct wave, arrive late at the image receiving point.

Due to this delay, the modulation signal of the ghost wave has a delay with respect to the modulation signal of the direct wave, and the carrier wave of the ghost wave has a phase difference with respect to the carrier wave of the direct wave.

On the other hand, since television signals are VSB (residual sideband) signals, waveform distortion occurs when a signal with a phase different from the reference direct wave is detected, and ghost waves cannot be canceled with only a simple delay circuit. It is not possible.

As a method of canceling ghost waves with different phases, video detection is performed using two phase detection circuits, the first detection phase is matched to the phase of the direct wave, and the second detection phase is set to the opposite phase to the ghost wave phase. A ghost cancellation method has been proposed that matches the phase of the ghost wave, but according to this method, it is necessary to determine one of the detection phases in relation to the phase of the ghost wave, so it is not possible to cancel multiple ghost waves with different phases. Can not.

- The present invention has been made in view of these points, and provides a ghost removal circuit that can cancel a single or multiple ghost waves and can also cancel orthogonal components of direct waves. Hereinafter, various embodiments of the present invention will be described in detail based on FIGS. 1 and 2.

FIG. 1 shows one embodiment of the present invention.
In the figure, 10 is a VIP amplification stage, which has normal characteristics.

Reference numeral 20 denotes a carrier wave extraction circuit composed of a narrow band amplifier, which generates a carrier wave having a reference phase.

A phase shift circuit 21 shifts the phase of the carrier signal from the carrier extraction circuit 20 to generate a detected phase axis signal (hereinafter simply referred to as a detected axis signal) of C05 (ωt+φ) at h.

22 is a one-lag phase circuit which delays the output signal of the phase shift circuit 2 π 21 by one phase and outputs h2−CO8(ωt+φ
−Σ) is generated.

23A and 23B are the first. A second phase detection circuit performs phase detection on the signals from the VIP stage 10 using the above h1 and h2 as detection axis signals.

30 is a delay circuit, and the delay time in this circuit is set to be substantially equal to the delay time of the ghost wave.

32A, 32B and 31 are the first. The second and third coefficient circuits, 33° and 34 respectively, are the first and third coefficient circuits. This is a second addition circuit.

The adder circuit 33 connects the output of the coefficient circuit 32A and the coefficient circuit 32B.
is configured to add the outputs of .

Further, the adder circuit 34 is connected to the output of the coefficient circuit 31 and the delay circuit 30.
The output of the phase detection circuit 23A is added to the output of the phase detection circuit 23A.

40 is an output terminal of the adder circuit 34.

Next, the operation of the coast removal circuit according to the present invention will be explained.

The output of the VIP amplification stage 10 is expressed as a carrier fraction, where ω is the frequency of the carrier wave in the intermediate frequency band, γ is the delay time of the ghost wave with respect to the direct wave, and G is the amplitude ratio.

Here, the first and second terms represent the in-phase and quadrature components of the direct wave, and the third and fourth terms represent the in-phase and quadrature components of the ghost wave, respectively.

The second and fourth terms are incidental because the television signal is a residual sideband signal, and a(t) and b(t) are orthogonal.

Further, α is the phase angle of the ghost wave with respect to the direct wave, the carrier co-wave number of the direct wave is ωc1, the delay time of the ghost wave with respect to the direct wave is γ, and ωCγ=−α+2nπ(U=O.

1.2. ......) is given.

Let the VIP amplification stage signal f given by equation (2) be h,=C
If phase detection is performed by the phase detection circuits 23A and 23B using 03(ωt+φ) and h22cos(ωt+φ−100) as detection axis signals, the output signals from the phase detection circuits 23A and 23B will be as follows.

Now, the phase detection circuit 2 shown by equations (3) and (4)
The outputs ul and u2 from 3A and 23B are combined by an adder circuit 33 through coefficient circuits 32A and 32B, respectively.

The output of the adder circuit 33 is delayed by the delay circuit 30 and then sent to the adder circuit 34.

The adder circuit 34 outputs the output u1tu'2 and the delay circuit 3.
Add the output of 0.

It is configured for

Further, the delay time of the delay circuit 30 is selected to be substantially equal to the delay time of the ghost wave.

When configured in this way, the output terminal 40 of the adder circuit 34
The video signal X obtained is as follows.

That is, if the third coefficient 41 of the coefficient circuit 31, the first coefficient of the coefficient circuit 32A is set to 1, and the second coefficient of the coefficient circuit 32B is set to 2, the above (6) is obtained. In the equation, the second, third, and fourth terms are zero.

Furthermore, the fifth and sixth terms will have an amplitude of about 02 if φ is chosen small, so even if there is a large ghost wave where G = 1, for example, the amplitude will decrease to about G2-1 and can be ignored. .

For example, if φ is selected as the composite liquid phase of the carrier phase of the direct wave and the carrier phase of the ghost wave, φ is 1φ1 even for a large ghost wave such as G=H, and the above argument can be fully understood. can do.

That is, the detection phase of one of the two phase detection circuits 23A is set to an arbitrary value approximately equal to the carrier phase of the direct wave, and the detection phase of the other phase detection circuit 23B is set to the detection phase of the phase detection circuit 23A. By assuming that the phase is delayed by 100 degrees and selecting 1°k2 for the coefficients l and 1°k2 of the coefficient circuits 31, 32A, and 32B as shown in equation (7), the output terminal 40 of the adder circuit 34 has A video signal that looks like this is obtained.

It is clear that this signal does not contain ghost waves and also does not contain components orthogonal to direct waves, so that distortion-free detection can be achieved.

FIG. 2 shows another embodiment of the present invention, in which the configuration is such that a plurality of ghost waves can be canceled.

In FIG. 2, 300 is a delay circuit with an intermediate input;
For example, the delay time γi from the first input tap to the output end is set to be equal to the delay time of the first ghost wave.

(32A-1), (32B-1), (32A-2),
...(32B n) is a coefficient circuit corresponding to the first ghost wave, (33-IL(33-2
), . . . (33-n) are force-rho calculation circuits corresponding to the first ghost wave as well.

The other configurations are the same as in the case of FIG.

With this configuration, the detection phase of the phase detection circuit can be set regardless of the phase of the ghost wave, as described with reference to FIG.

Therefore, the first coefficient circuit (32A-i) (32B
The first ghost wave can be canceled if the coefficient of i) is set to 1 is k2 t for the first ghost wave, so this can be set to t==1.2.・・・・・・・・・
. . , n, it is possible to cancel n ghost waves.

Although the delay circuit has been described as having an intermediate tap, the above argument can be satisfied even if the delay circuit is configured with a plurality of delay circuits having different delay times.

As described in detail above, according to the coast removal circuit according to the present invention, by configuring the detection phase axis of the phase detection circuit to be independent of the phase of the ghost wave,
It is possible to cancel a single ghost including its orthogonal components, and it is also possible to cancel a plurality of ghosts including their orthogonal components.

Furthermore, since the orthogonal components of the direct waves can also be canceled, a ghost-free received signal can be obtained without distortion.

Furthermore, in the ghost removal circuit according to the present invention, since the delay circuit is used in the video same wave number band, more stable characteristics can be achieved than in the case of canceling in the intermediate frequency band.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the invention, and FIG. 2 is a block diagram showing another embodiment of the invention. In the figure, 20 is a carrier wave extraction circuit, 21 is a phase shift circuit, 22 is a hundred phase delay circuit, 23A and 23B are first and second phase detection circuits, respectively, 30 is a delay circuit, and 32A. 32B and 31 are the first. Second. The third coefficient circuits 33 and 34 are respectively the first . second addition circuit, 32
A-1, 32B-1, ... (32An), (3
2B-n) is a coefficient circuit, (33-1) (33-2),
..., (33-n) is an adder circuit, and 300 is a delay circuit. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A carrier extraction circuit that extracts a carrier signal with a reference phase from a received broadcast wave, and generates a detected phase axis signal by shifting the phase of the carrier ω to h1=CO8(ωt+φ). a first phase detection circuit that responds to these two signals and detects the phase of the signal from the VIP stage using hl as a detected phase axis signal;
a phase delay circuit that generates a detection axis signal with a phase delay of 2 and h2 = CO8 (ωt + φ - Σ); a second phase detection circuit that detects the phase of the signal from the VIP stage using h2 as the detection phase axis signal; The first coefficient, number 1--G bamboo "yu" 0. 2=-GSln(φ+a) for the coefficient of the 2nd cosφ, 3rd (D coefficient 1
cosφ is set to be profitable (however, α is the goth cos
φ is the phase angle of the ghost wave with respect to the direct wave, G is the amplitude ratio of the ghost wave with respect to the direct wave) first, second and third coefficient circuits;
Each output signal of the first and second phase detection circuit is
, a first addition circuit that performs post-addition through a second coefficient circuit, and a delay circuit that delays the output signal of the first addition circuit and whose delay time is set to be substantially equal to the delay time of the ghost wave. and a second circuit for obtaining a video signal by adding the output signal of the delay circuit, the output signal of the first phase detection circuit, and the output signal obtained from the second phase detection circuit through the third coefficient circuit. A ghost removal circuit equipped with an adder circuit.