JP2734196B2 - Ghost removal device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost elimination circuit for eliminating group delay distortion, frequency characteristic distortion, ghost, and the like generated during transmission of a television signal.

[Conventional technology]

The television signal demodulated by the television receiver is
In addition to the signal received by the direct antenna (hereinafter referred to as a direct wave), a signal (hereinafter referred to as a reflected wave) which is received after being reflected by a building, a mountain, an airplane, or the like is superimposed. The reflected wave has a reduced energy due to a longer transmission path distance from the direct wave, and is slightly delayed. For this reason, a multiplex image is generated in addition to the original image on the demodulated television screen. This multiple image is called a ghost, and the image quality deterioration due to the ghost is called a ghost disorder.

A conventional ghost removing device for removing this type of ghost will be described with reference to FIG. The input terminal 1 is an input of a composite television signal. An analog-digital converter (hereinafter, A / D converter) 2 converts a television signal output from the input terminal 1 from analog to digital. The configuration of the ghost removal filter 26 includes a delay circuit 4 for delaying the television signal after the pre-digital conversion for an arbitrary time, and a transversal filter for arbitrarily changing the gain of the television signal output from the delay circuit 4.
28 and an adder 8 for adding the signal output from the transversal filter 28 to the television signal output from the analog-digital converter. A digital-analog converter (hereinafter, D / A converter) 9 performs digital-analog conversion on the output of the adder 8.

The ghost elimination reference signal detection circuit 11 detects a ghost elimination reference signal superimposed on the television signal. The ghost detection circuit 12 detects a ghost state from the distortion of the ghost removal reference signal detected by the ghost removal reference signal detection circuit 11. The delay amount control circuit 13 changes the delay amount of the delay circuit 4 according to the state of the ghost. The filter control circuit 27 controls the gain of the transversal filter 6 to an optimum state. More specifically, the ghost is removed by controlling the delay circuit 4 and assigning the transversal filter 28 to the position where the ghost exists.

The transversal filter 28 will be described with reference to FIG.

The minimum unit is composed of a combination of delay circuits 15a to 15f for delaying input data by at least one clock time and multipliers 16a to 16f. The adder 17 adds the outputs from the plurality of multipliers 16a to 16f and outputs the sum. The coefficient memory 18 stores the coefficients of the multipliers 16a to 16f.

The size of the transversal filter is proportional to the data length of the data input and the data length of the coefficient. A / D converter 2
Is 8 bits, the ghost removal filter 26
The bit length of the video signal of the transversal filter 28 and the bit length of the coefficient input from the filter control circuit 27 are about 10 bits because the bit length of the cyclic portion of It is getting longer. The number of taps required to cover the entire ghost removal range (typically about 42 μS) is 640 taps. Even if it covers a range of about 2/3, 400 taps or more are required.

[Problems to be solved by the invention]

The ghost state changes depending on external factors such as channel, region, and the like. However, the number of ghosts with large energy actually varies depending on the area, but is at most about four. In many cases, ghosts having low energy are generated on the screen so as to overlap each other.

In the above-described conventional ghost removal apparatus, since the bit lengths of the data and coefficients of the transversal filter are all as long as about 10 bits, a ghost having a small energy is assigned a filter of the same scale as a ghost having a large energy. I have. For this reason, there is a disadvantage that the circuit scale of the ghost removing device becomes large.

[Means for solving the problem]

In order to solve the above-mentioned problem, the present invention provides a conventional ghost elimination device with a transversal
The filter includes a plurality of trans-versal filters having different bit lengths, and selects and controls trans-versal filters having different bit lengths according to the detected ghost state.

Transversal for ghost removal filter
The filter has a plurality of trans-versal filters having different bit lengths, and has a multiplier at the output of the trans-versal filter having a short bit length.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. The input terminal 1 inputs an analog television signal. The A / D converter 2 performs analog-to-digital conversion of a television signal output from the input terminal 1. The ghost removal filter 3 constitutes a recursive filter and removes ghosts. The ghost removal filter 3 includes delay circuits 4 and 5 for delaying a digital video signal, a transversal filter 6 for controlling the gain of the video signal output from the delay circuits 4 and 5 with a plurality of taps, and a transversal filter. 7 and a transversal filter 6, an adder 8 for adding the output of the transversal filter 7 and the output of the A / D converter 2. The delay circuit 4 and the transversal filter 6 have the same data length as the conventional ghost removing device and reduce the number of taps to 1/2 or less. The delay circuit 5 and the transversal filter 7
The data length is short. Here, the trans-versal filter 6 and the trans-versal filter 7 are combined so as to be about 2/3 of the conventional transversal filter 28. The D / A converter 9 converts the digital video signal output from the ghost removal filter 3 into analog. The output terminal 10 externally outputs the video signal output from the D / A converter 9.

The ghost elimination reference signal detection circuit 11 detects the position of the ghost elimination reference signal superimposed on the video signal from the analog video signal output from the input terminal 1 and detects at least the output of the A / D converter 2 and the adder 8. One of the output digital ghost removal reference signals is detected and corrected by correcting the delay in the apparatus, and the captured ghost removal reference signal is output to the ghost detection circuit 12. The ghost detection circuit 12
The distortion of the ghost elimination reference signal input from the ghost elimination reference signal detection circuit 11 is analyzed to determine the optimal cyclic characteristic of the ghost elimination filter 3 for ghost elimination, and is output to the delay amount control circuit 13 and the filter control circuit 14. . The delay amount control circuit 13 analyzes the cyclic coefficient input from the ghost detection circuit 12 and controls the delay circuits 4 and 5. Filter control circuit 14
FIG. 6 shows a flow chart of the operation of FIG. The filter control circuit 14 analyzes the cyclic coefficient input from the ghost detection circuit 12 and controls the transversal filter 6 in accordance with the energy of the ghost, starting from the one with the larger energy.
Next, the transversal filter 7 is controlled from the one with the largest energy.

The transversal filter 7 will be described with reference to FIG. It comprises a combination of delay circuits 19a-f for delaying input data by at least one clock time and multipliers 20a-f, and an adder 21 adds outputs from the plurality of multipliers 20a-f and outputs the sum. The coefficient memory 22 includes multipliers 20a to
The coefficient of f is recorded. The data length of the video signal is 6 bits, and the bit length of the filter control coefficient is 5 bits.

FIG. 4 shows a second embodiment of the present invention. Input terminal 1, A /
D converter 2, delay circuits 4 and 5, trans-versal filter 6, trans-versal filter 7, adder 8, D /
The A converter 9, output terminal 10, ghost removal reference signal detection circuit 11, ghost detection circuit 12, and delay amount control circuit 13 are the same as those in the previous embodiment.

The ghost removal filter 23 is a ghost removal filter 3
, A multiplying circuit 24 is added to the output of the transversal filter 7. In order to prevent the ghost from remaining due to a large number of ghosts having a large energy and a short bit of the transversal filter 7, the multiplication circuit 24 further controls the gain of the output of the transversal filter 7 by controlling the gain. Output. The adder 8 adds the output of the multiplication circuit 16 and the output of the A / D converter 2 and outputs the sum.

The filter control circuit 25 controls the trans-versal filter 6, the trans-versal filter 7, and the multiplying circuit 24 in descending order of ghost detected by the cyclic characteristic input from the ghost detection circuit 12.

〔The invention's effect〕

As described above, the present invention is different from the conventional ghost removal apparatus in that a transversal filter used for a ghost removal filter is provided with a plurality of transformers having different bit lengths.
A transversal filter having a shorter bit length among a plurality of trans-versal filters having different bit lengths; For ghosts with large energy, control the trans-versal filter with a long bit length,
For a ghost having small energy, controlling the transversal filter having a short bit length has the effect of reducing the circuit scale of the ghost removing device without deteriorating the ghost removing performance.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of a ghost removing device according to the present invention. FIGS. 2 and 3 are block diagrams of a transversal filter used in the first embodiment. Is a block diagram of a second embodiment of the present invention, FIG. 5 is a block diagram of a conventional ghost removing device, and FIG. 6 is a flowchart of the operation of the filter control circuit 14. 1 ... input terminal, 2 ... A / D converter, 3 ... ghost removal filter, 4 ... delay circuit, 5 ... delay circuit, 6 ...
Transversal filter, 7 Transversal filter, 8 Adder, 9 D / A converter, 10
…… Output terminal, 11 …… Ghost removal reference signal detection circuit,
12 ghost detection circuit, 13 delay amount control circuit, 14
... Filter control circuit, 15 ... Delay circuit, 16 ... Multiplier,
17 ... Adder, 18 ... Coefficient memory, 19 ... Delay circuit, 20
…… Multiplier, 21 …… Adder, 22 …… Coefficient memory, 23 ……
Ghost removal filter, 24 Multiplier, 25 Filter control circuit, 26 Ghost removal filter, 27 Filter control circuit, 28 Transversal filter.

Claims (2)

(57) [Claims] An A / D converter for converting a television input signal supplied to an input terminal from analog to digital to generate a digital video signal; a means for detecting a ghost removal reference signal from the digital video signal; Means for detecting a ghost based on a ghost removal reference signal, first and second delay circuits for setting a delay amount and delaying the digital video signal, and a second circuit to which an output signal of the first delay circuit is inputted. 1 trans-versal filter, a second trans-versal filter to which an output signal of the second delay circuit is input and which has a shorter bit length than the first trans-versal filter, and an energy of the ghost. The first and second
Means for setting the delay amount of the delay unit and the gains of the first and second transversal filters, respectively, and the output signal of the first and second transversal filters is converted to the digital video signal And a D / A converter for digital-to-analog conversion of the output signal of the adder, wherein the second signal is output based on the ghost energy.
A ghost eliminator, further comprising means for changing a gain of an output signal of the transversal filter. 2. The apparatus according to claim 1, wherein said plurality of first and second transversal filters are provided.
2. The ghost eliminator according to claim 1, wherein the number of the versal filters is larger than that of the first trans versal filter.