JPS6380683A - Ghost removing device - Google Patents

Abstract

PURPOSE:To reduce the scale of a hardware compared with the case of using a multiplier and to reduce cost by constituting a digital transversal filter by using a two's power coefficient multiplier. CONSTITUTION:A digital video signal is supplied to the digital transversal filter 212 through an alpha multiple coefficient multiplier 210 and a variable delay circuit 211. The transversal filter 212 consists of unit delay elements 311-314 connected in a series, the two's power coefficient multipliers 411-415 and a adder 511 to synthesizes the output of of each of the two's power coefficient multipliers 411-415, and a ghost removing signal is obtained from the adder 511. The ghost removing signal is added to an inherent video signal from an input terminal 12 in the adder 213, then the digital video signal, from which the ghost is removed, is obtained from the adder 213.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Field of Industrial Application) This invention relates to a ghost removal device for removing ghosts from television signals.

(Prior Art) There is a device that uses an equalization circuit to automatically and digitally remove television ghosts. Figure 2 is an example. The details of the operation of this device can be found in the literature (Haka Murakami “Digitalized Ghost Automatic Eraser” Technical Research Report E of Institute of Electronics and Communication Engineers)
MCJ78-37.November 1978).

This device is entirely digitalized, and a digital video signal including ghosts is input to an equalization circuit 2 via an input terminal 1. This equalization circuit 2, as shown in FIG.
N+M unit time delay elements 201 (delay time Tsec
), N+M+1 tap coefficient units 202 (digital multipliers), an adder 203 for adding together the outputs of the respective tap coefficient units, and a tap gain memory 204.

The tap coefficients C(-M) to C(material) of this tap coefficient multiplier are set to appropriate values by the control circuit 3, and a digital video signal from which ghosts have been removed is outputted to the output terminal 5.

The reference signal for removing ghosts is the differential waveform of the trailing edge a of the vertical synchronization signal shown in FIG. The peak corresponding to the falling portion of the trailing edge is set as a time reference 0, and each peak di after this time reference is detected.

J, I (i--M-snoring)... (1) This differential value d1
The sign corresponds to the positive and negative of the residual ghost having the delay time iT. Therefore, the knob gain correction circuit 31 uses this differential value d1 to sequentially correct each tap gain according to the following equation.

C1, new −C1, old−Δ・sgn di(1
--M-N, l≠0>...(2) Here, C1, ol
d is the tap gain before correction, Ci.

new is the tap gain after correction, Δ is a small positive correction coefficient, and equation (2) is widely known as the Zero Forcing method. Note that the center tap coefficient CO is C
It is fixed at 0-1...(3). Every time a vertical synchronization signal arrives (176
0 seconds), the ghost is removed by performing this sequential correction.

The sequence controller 4 includes the control circuit 3 described above.
It can be configured using, for example, a ROM. There is also a known device that removes ghosts using a combination of fixed delay circuits and a transversal filter (Japanese Unexamined Patent Publication No. 158579/1983) (Problems to be Solved by the Invention) However, the conventional Digital ghost removal equipment requires a large number of coefficient units (multipliers) in order to perform sufficient ghost removal, and the general-purpose digital multipliers used for these coefficient units are expensive and large in size. Due to its large size (one multiplier is one IC), a practical ghost removal device could not be obtained. on the other hand,
Although an analog equalization circuit using a CCD has been put to practical use as a ghost removal device, it has problems in terms of residual image and S/N ratio.

The equalization circuit used in the ghost removal device that has already been put into practical use is as described in Document 3 (Murakami et al. "Ghost Clean System" Toshiba Review Vol. 38 No. 7 June 1982). CCD (ChargeC
(devicc) This uses a transversal filter. However, since this is an analog signal processing device, the linearity of the coefficient unit (multiplier) and the overall S/N were insufficient. This drawback, when viewed as a ghost removal device, has led to an increase in ghosts remaining on the screen and a decrease in S/H.

Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 58-158579 also has a problem in that grandchild ghosts remain even if the ghosts are removed at the primary ghost removal stage.

Therefore, this invention was made to solve the above-mentioned problems.It does not require a multiplier, has sufficient ghost removal performance, and can be used in practical applications in terms of mooring and hardware. The purpose is to provide a removal device.

[Structure of the Invention] (Means for Solving the Problems) This invention adjusts the time difference between a television signal including a ghost and a ghost signal using a variable delay circuit, and supplies the adjusted signal to a digital transversal filter. When a ghost-removed signal is generated, a multiplier is not used in this transversal filter, but a power-of-two coefficient multiplier is used to generate an approximate ghost-removed signal. The residual ghost component generated by generating the ghost removal signal with a power-of-two coefficient multiplier is suppressed by controlling the α multiplier provided in the front stage of the variable delay circuit to the extent that it does not pose a visual problem. It is intended to reduce

(Function) According to the present invention, since the power coefficient multiplier of 2 is used, it is possible to realize a digital equalization circuit with a much smaller hardware scale than when a multiplier is used. Therefore,
The device as a whole has a small number of taps, is advantageous in terms of price, and has a simple hardware configuration. It also has good ghost removal performance and can provide a television signal with a good S/N ratio.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a digital video signal is input to an α multiplier 210 via an input terminal 11 and multiplied by α. The output of this α multiplier 210 is supplied to a variable delay circuit 211, time-adjusted, and supplied to a digital transversal filter 212. The digital transversal filter 212 uses a human signal to
Ghost removal signal (a signal that corresponds to the ghost position of the television signal and has a polarity opposite to that of the ghost, and that cancels the ghost when added to the television signal)
generate. Therefore, the variable delay circuit 211 described above is
It is provided to compensate for the time difference between the original television signal and the ghost signal.

The transversal filter 212 includes, for example, unit delay elements 311 to 314 connected in series, and power-of-2 coefficient units 411 to 4 to which inputs and outputs of each unit delay element are supplied.
15 and an adder 511 that combines the outputs of each of the power-of-two multipliers 411 to 415, and obtains a ghost-removed signal from the adder 511. The ghost removed signal is sent to the adder 213
At , it is added to the original video signal from input terminal I2. As a result, a digital video signal from which ghosts have been removed is obtained from the adder 213, and this signal is supplied to the latch circuit 215. The latch circuit 215 is for synchronizing the signal delay time with the system clock.

The equalization unit memory 214 includes the coefficient unit 210 and the variable delay circuit 2 so as to obtain a ghost removal signal effective for removing ghosts included in the television signal.
11 delay amounts and coefficients of power of 2 coefficient units 411 to 415 are stored.

The above example is shown as a circuit for removing one ghost. That is, ideally, the ghost signal removed has a waveform of opposite polarity as shown in FIG. 5(b) with respect to the ghost signal shown in FIG. 5(a). In this invention, since a power-of-two coefficient unit is used instead of a multiplier, the ghost removal signal becomes a signal approximated by discrete values as shown in FIG. 5(C). The result of adding the ghost signal (a) and the ghost removed signal (C) is the signal shown in FIG. 5(d). In other words, simply adding the ghost removal signal (C) will result in some remaining parts. However, in this invention, by adjusting the coefficient unit 210, the ghost removed signal becomes as shown in FIG. (Fig. 5(f))
).

In particular, very good cancellation was obtained for removing a single ghost signal.

FIG. 6 shows the circuit of FIG. 1 further divided into blocks. Therefore, the same parts as in FIG. 1 are given the same reference numerals.

FIG. 7 shows that in order to remove a plurality of ghosts, a plurality of equalization units as shown in FIG.
The signal is added to the input video signal to remove ghosts. The equalization units Y1 to Y3 have the same circuit configuration as shown in FIGS. 1 and 6, and use a power-of-2 coefficient unit.

Now, as shown in FIG. 8, three ghosts g1, g2.
g3 shall be removed. The equalization unit Y1 uses the output of the adder 701 to create a ghost removal signal gll (FIG. 8(b)), and supplies this to the equalization unit Y2. This equalization unit Y2 uses the output of the adder 701 to create a ghost removed signal g12 corresponding to the ghost g2, and also creates a ghost removed signal gl at a different time position.
(Fig. 8(C)). This signal is fed to equalization unit Y3. This equalization unit Y3 uses the output of the adder 701 to create a ghost removal signal g13 corresponding to the ghost g3, and synthesizes it with ghost removal signals gll and g12 at different time positions (FIG. 8(d)).
). As a result, a ghost removal signal having a polarity completely opposite to that of the plurality of ghosts shown in FIG. 8(a) is obtained, and the ghosts are canceled by the adder 701.

To detect ghosts, the signal y at the leading edge of the vertical synchronization signal
k (FIG. 8(d)) is detected by differentiation in the control circuit 703, and is taken into the output waveform memory of the control circuit as a differential value dk. This operation is performed every time a vertical synchronization signal arrives. The control circuit 703 detects the maximum peak value of the differential value dk, and sets the data position as the time reference TΦ. This time reference corresponds to the main signal phase. Next, the second peak value, the third peak value, and the fourth peak value are detected, and these data positions are regarded as the first to third ghost positions, and each equalization unit Y1 to Y3 is The delay amount of the variable delay circuit of each unit is controlled through a control line so as to be assigned to a ghost.

Next, each tap gain Ct of each equalization unit is modified according to the following equation.

Ci, new = C1, old −Δ
・sgn dl(1-Ichikawa~N, i≠0〉・
...(2) Here, Ci, old is the tap gain before modification, C1゜new is the tap gain after modification, △ is a positive minute modification coefficient, and sgn di is the output corresponding to the sample timing TΦ This is the sign of the sample value of the differential value d of the signal y. By modifying in this way, it is possible to obtain a ghost cancellation signal having the same time position and amplitude (opposite polarity) of each ghost.

[Effects of the Invention] As explained above, the present invention can provide a ghost removal device that does not require a multiplier, has sufficient ghost removal performance, and is practical in terms of price and hardware. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a system explanatory diagram of a ghost removal device, Fig. 3 is a circuit diagram of a conventional transversal filter, and Fig. 4 explains a ghost detection method. FIG. 5 is a signal waveform diagram for explaining the ghost removal process of the device of this invention, FIG. 6 is a block diagram showing the circuit of FIG. 1, and FIG. FIG. 8 is a block diagram showing the embodiment and is a signal waveform diagram for explaining the ghost removal process. 210...Coefficient unit, 211...Variable delay circuit, 21
2... Transversal filter, 213.511.
... Adder, 124 ... Equalization unit memory, 215
...Latch circuit, 311-314...Unit delay element, 411-415...2 power factor unit.

Claims (2)

[Claims] (1) A coefficient multiplier that multiplies the video signal input to the first input terminal by α, a variable delay circuit that delays the output signal according to a control signal, and a plurality of unit time delay elements connected to each of them. a digital transversal filter comprising an approximate tap coefficient unit of a power of 2; a memory for storing a gain value in the tap coefficient unit of the transversal filter and a delay time in a variable delay circuit; and a means for synthesizing the ghost-removed signal into a video signal. (2) A coefficient multiplier that multiplies the video signal input to the first input terminal by α, a variable delay circuit that delays the output signal according to a control signal, a plurality of unit time delay elements, and these unit time delay elements A plurality of equalization units each consisting of a digital transversal filter consisting of a power-of-two approximate tap coefficient unit connected to each of A ghost removal device comprising: means for adding.