JPH02285866A - Ghost eliminator - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy of a ghost by performing the elimination of jitter of a reference signal fetching pulse by peak alignment when taking addition mean at an addition averaging circuit. CONSTITUTION:The device is equipped with an error check circuit 31, a low-pass BPF(band-pass filter) 32, a peak detection circuit 33, a delay compensation circuit 34, an OR circuit 35, and a switch 36, and those components are inserted between a waveform extraction circuit 12 and the addition averaging circuit 13. When the addition mean is taken, plural constant periods are further pro vided at the period of a reference signal, and when a signal of level separated remarkably that is not an ordinary ghost is detected in the period where no peak is detected in the constant period in the neighborhood of a regular peak or in the period other than that, a fetch signal is prevented from being added on the addition mean. Therefore, it is possible to eliminate the jitter of the reference signal fetching pulse by the peak alignment at the time of taking the addition mean at the addition averaging circuit 13, and to improve the detecting accuracy of the ghost.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a ghost removal device, and in particular, to a ghost removal device that removes ghosts and waveform distortion contained in input video signals in various video equipment that receives TV (television) video signals. Regarding the ghost canceller to be removed.

[Conventional technology]

High-definition, reflecting the recent trend toward higher image quality and larger screens in monitor devices such as TV receivers (mR).

High-definition TV broadcasting systems, such as Clear Vision, are attracting attention. On the other hand, ghost interference, which occurs due to the simultaneous reception of reflected waves from skyscrapers and mountainsides, is becoming a new problem. Moreover, due to the increase in the number of high-rise buildings, etc., the interference area is expanding, and this is due to
It has become necessary to reduce or even eliminate ghost interference in television receivers, and in particular, high-end TV receivers are required to be equipped with a ghost removal device to remove ghost interference.

A conventional ghost removal device will be explained with reference to FIG. Figure 2 shows a typical conventional ghost removal device 1.
8 is an A/D converter, 9 is a timing signal generation circuit, and 11 is a transversal filter (FIR filter).

11 is a synthesis filter consisting of an R filter, etc.), 12 is a waveform extraction circuit, 13 is an averaging circuit, 14 is a differential filter,
15 is a subtracter, 16 is a magnification setting circuit, 17 is a weighting setting circuit, and 18 is a reference waveform generation circuit. The timing signal generation circuit 9 generates a timing signal based on the horizontal synchronization signal and/or the vertical synchronization signal included in the input video signal, and supplies this to the reference waveform generation circuit 18 to generate a waveform extraction diagram. 112 and the reference waveform generation circuit 18 are synchronized.

The input video signal X (t) (A/D converted) supplied via the input line 11 is passed through the transversal filter (hereinafter also simply referred to as "filter j") 11 to the output video signal Y from the line 12. (t) and is supplied to the waveform extraction circuit 12, where a predetermined fixed period (for example, one horizontal scanning line) including the reference signal is extracted.The reference signal period extracted from the input video signal X lt) (hereinafter also referred to as "taken signal") is the averaging circuit 13
In order to improve the S/N of the captured signal, averaging is performed. Averaging is the process of capturing the period in which the reference signal for ghost removal contained in the TV video signal is superimposed several times (by aligning the position of the captured signal with a certain reference position), and then calculating the average. It is to take a value.

Here, reference waveforms for detecting waveform distortion such as ghosts in the input video signal will be explained with reference to FIG. 3. Figures (A) and (B) show step-like signals superimposed over one horizontal scanning period. Each falling edge is used as a reference signal. In this case, the rising
It is assumed that the frequency characteristics around the falling edge are predefined.

Further, although FIG. 2C shows a vertical synchronizing signal, the falling portion of this signal can also be used as a reference signal.

FIG. 4 shows a conventional configuration example of the waveform extraction circuit 12 and the averaging circuit 13. In FIG. The operation of extracting the reference signal from the input video signal is performed by a switch 24 that is opened (ON) only when a "reference signal period sampling pulse" (reproduced from the input video signal) is supplied from the input terminal In2. A captured signal is obtained and output to the adder circuit 22. The averaging operation is performed by adding a signal previously written to the memory 23 (up to an arbitrary time) and a signal newly taken in from the switch 24 in the adding circuit 22, and writing a new signal to the memory 23. This is done by inserting the

The acquired signal that has been averaged a predetermined number of times is extracted by the switch 25, which is closed only when an “average result extraction pulse” (reproduced from the input video signal) is supplied from the input terminal In=, and is differentiated. The signal is output to the filter 14, where differentiation is performed to suppress the influence of DC fluctuations, for example.

The output signal of the differential filter 14 is supplied to a subtracter 15,
Here, comparison (in this embodiment, subtraction) is performed with the original reference signal waveform (internal reference waveform) calculated in advance in the reference waveform generation circuit 18. Based on the result of this comparison (error signal sequence), a predetermined magnification is set in the magnification setting circuit 16. This magnification is output to the weighting setting circuit 17 at the next stage, where the weighting is set by multiplying the output of the subtracter 15, that is, the subtraction result (error sequence) by the magnification, and is supplied to the transversal filter 11. Determine the tap gain of each filter that makes up this.

As a result, the transversal filter 11 outputs a video signal from which ghosts have been removed (reduced). Since the weighting setting circuit 17 requires the function shown in Figure 3,
It consists exclusively of a microcomputer (licro C01putOr) and a microprocessor.

Note that the circuit shown in FIG. 2 uses a filter 11 to extract the reference signal.
This is an example of a configuration of a feedback type control in which the tap gain is updated sequentially from the output side of the filter 11.In addition, the reference signal is extracted from the input side of the filter 11, and the tap gain is determined based on the past tag gain. There is also feedforward control that does not use filter output. In either case, the random noise component included in the reference signal portion of the input video signal is reduced by the averaging circuit 13.

[Problem to be solved by the invention]

In the above conventional ghost removal device, the reference signal period sampling pulse used in the averaging circuit 13 can be regenerated stably under good reception conditions, but when the S/N is poor or a nearby ghost is added, In some cases, only unstable playback with fluctuations is possible. The reason for this will be explained with reference to the timing chart of FIG.

If the reference signal period sampling pulse has jitter, conversely, if we fix the reference signal period sampling pulse (relatively) and consider it, the captured signal each time will be as shown in Figures 5 (B) to (E).
There will be jitter as shown in . If these signals are directly added together in the averaging diagram 17813, the ghost contained in the captured signal cannot be detected accurately, and therefore the ghost cannot be accurately removed.

Also, if some sudden error occurs in the reference signal period before the waveform extraction circuit, or if a signal different from the reference signal is mixed in the reference signal sampling pulse period, if this is added and averaged as is, By detecting a signal that is completely different from a ghost and performing a removal operation, CR
There has been a problem in that the output image on the display screen of the T or the like is seriously hindered.

[Means for Solving the Problem] In addition to the conventional configuration, the ghost removal device of the present invention has a configuration between the waveform extraction circuit and the averaging circuit, which has a level different from a preset error check threshold. From the error check circuit that generates an NG signal when a signal is detected and the signal captured by the waveform extraction circuit,
a low frequency BPF that extracts the peak as a reference position; a peak detection circuit that generates an NG signal when the peak extracted by the low frequency BPF is not at a predetermined level or higher;
A switch means is inserted that outputs the output signal of the waveform extraction circuit when no NG signal is generated from the error check circuit and the peak detection circuit, and outputs MON when an NG signal is supplied from at least one of the circuits. The above problem has been solved by configuring the averaging circuit to perform averaging so that the peak positions given from the peak detection circuit match only when no NG signal is generated.

〔Example〕

An embodiment of the ghost removal device of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of a ghost removal device 10 of the present invention, and in this figure, the same components as those of the conventional device shown in FIG. As is clear from a comparison of both figures, the ghost removal device 10 of the present invention includes error check circuits 31 . Low-pass BPF (band pass filter) 32. Peak detection port I? 833. Delay compensation circuit 34. The circuit includes an OR circuit 35 and a switch 26, which are connected as shown in the first figure and inserted between the waveform extraction circuit 12 and the averaging circuit 13.

With this configuration, when averaging, a plurality of fixed 71 intervals are further provided within the reference signal period, and a reference signal that is not a normal ghost is detected during a period in which no peak is detected in a fixed period around the original peak, or in other periods. If a signal with a level far different from the signal is detected, the captured signal is not added to the averaging.

Therefore, it is possible to remove the irregularity of the reference signal acquisition pulse (reference signal period sampling pulse) due to peak matching during addition and averaging in the addition and averaging port l1I813, and the detection accuracy of ghosts is improved. Furthermore, by using the low-pass BPF 32 for peak detection, the rising (or falling) of a step can be detected without being affected by noise or ghosts. Furthermore, when a peak cannot be detected during averaging, or when a waveform extremely different from a normal signal with a ghost is detected, by excluding that signal, malfunctions in abnormal situations can be prevented. Furthermore, since a peak also appears in the signal after differentiation, when controlling only the center tap of the filter 11 individually and controlling the DC'j gain of the filter 11, if the tap gain of the filter 11 is not so large, First, one or more operational features that are easy to control enable stable and reliable ghost removal.

Next, a more specific operation of the ghost removal device 10 of the present invention will be explained along the configuration of FIG. 1 with reference to the principle explanatory diagram of FIG. 6. The input video signal supplied from the input line J+ is supplied to the waveform extraction circuit 12, where it is extracted for a predetermined fixed period (for example, one horizontal scanning line) including the reference signal, and then processed by the error check circuit 31 and delay compensation. It is supplied to circuit 34.

First, the error check operation in the error check circuit 31 and the operation in the peak detection circuit 33 will be specifically explained. An error check period as shown in Figure 6 is provided within the reference signal period, and if a signal larger (or smaller) than a preset error check threshold level is detected during that period, the error check circuit 03 times R35 generated NG signal from 31
supply to. The error check threshold level is set as shown in FIG. 3(A) so that, for example, even if a ghost with a DU ratio of 6 dB is added, it will not be detected as an error.

It is set to about half the step height of the step reference signal shown in (B). Also, a peak search period is provided within the reference signal period, and during that period.

Even if a peak of a certain level (for example, half the level of the signal obtained by differentiating the original reference signal) or higher is not detected, the peak detection circuit 33 generates an NG signal and supplies it to the OR circuit 35. In this way, error checking and peak detection can prevent a large number of cases, such as when an error suddenly occurs in the ghost removal device 10 or when a signal other than the reference signal is mixed into the reference signal period. It can be detected as an NG signal.

Here, a specific example of the configuration and operation of the error check circuit 31 will be explained with reference to FIG. 7. The error check circuit 31 includes a switch 27, a comparator 36 . Flip-flop circuit 39. It consists of a latch circuit 40 and the like.

The output signal of the waveform extraction circuit 12 is input to the input terminal In.

Closed by the error check period gate pulse from (
ON), it is output from the switch 27 and supplied to the comparator 36. A preset error check threshold level β is applied to this comparator 36 from the input terminal 1n5, and when the output α from the switch 27 is greater than this level β, the three flip-flow 71 circuits are activated. A pulse for informing the end of the error check period is supplied to the flip-flop circuit 39 and latch circuit 40 from the input terminal 1n6, which is set (or may be configured to be set when β>α). The flip-flop circuit 39 is activated when the error check is completed (
That is, when the error check period end pulse is supplied, it is latched by the latch circuit 40 and sent to the line 111 as an NG signal.
is output from the next stage's OR circuit l? 835.

At the same time, the three flip-flop 71 circuits are reset and ready for the next acquired waveform.

Note that the captured waveform is output as is from the line 17 and is supplied to the next-stage low-band BPF 32.

Here, the low-band BPF 32 is configured to block DC components within the TV video signal band, but to pass frequency components in a very low band. The output of the low-band BPF 32 is supplied to a peak detection circuit 33 to detect the maximum value of the signal.

Next, referring to FIG. 8, we will explain the specific configuration example and operation of the low-band BPF 32 and the peak detection circuit 33. In FIG. f 5,43.588H2)
If sampled at
f, core 0nsl, 11 to Its are sign inverters (inverters), and 41 is a combiner, and the low-band BPF 32 is constituted by each of the above elements.

The captured signal coming from the input terminal 1n7 is sequentially delayed by unit time by each unit delay circuit [111 to DL32], and some of the signals are inverted by sign inverters 11 to I16, and then synthesized by a synthesizer 41. Ru. In this configuration, the tap gain of the low-pass BPF 32 is [-1,i.

..., -1, 0, 1, 1, ..., 1.1] (in this example, there are 16 -1s and 16s each).

The output a of the synthesizer 41 (i.e., the low-band BPF 32) is supplied to the next stage comparator 37 (maximum value selection circuit 37), where the threshold level of the peak search stored in the memory 42 (this is (which is the initial value at the start of the peak search period) or the maximum value of the output from the synthesizer 41 in the past (stored up to that time) within the peak search period, and the larger one is stored as the maximum value. The data is newly stored in the storage device 42. When the maximum value is updated in this way, the memory 4 is sent from the comparator 37 via the OR circuit 46.
A write (write) signal is supplied to the position counter 3, and the value of the position counter 44 at that time is stored in the memory 43. The value stored in the memory 43 is latched by the latch circuit 45 at the end of the beak search period.

The position counter 44 is reset at the start of the peak search period, and the count value of the position counter 44 at that time is simultaneously stored in the memory 43. Therefore, the output of the latch circuit 45 becomes a value representing the maximum value (that is, the position of peak 1ift) of the output of the low-band BPF 32 within the beak search period. If no signal having a level above the search threshold level appears, a value representing the position at the beginning of the peak search period is output. It is output to the averaging circuit 13, and is also output to the comparator 3.
8. This comparator 38 compares the value (b) of the position counter 44 at the start of the peak search period, and if a=b, it is determined that the predetermined peak did not appear within the peak search period, and an NG signal is sent to the line. 16 (
and the OR circuit 35) to the switch 26.

Here, if a peak search filter (corresponding to the low-pass BPF 32) is used, for example, with a tap gain of [-1, 0, 1], its frequency characteristic will be as shown in curve a in Figure 9. Within the band, the characteristics are close to those of an HPF (high-pass filter), making it more susceptible to the effects of noise and ghosts contained in the captured signal, making it easier to falsely detect peaks.
On the other hand, the frequency characteristic of the filter in the ghost removal device of this embodiment is as shown by the curve in the same figure.
Therefore, it is difficult to be affected by noise and ghosts contained in the captured signal, and peaks can be detected stably.

On the other hand, the output of the waveform extraction circuit 12 is transmitted to the delay compensation circuit 3.
The signal is also supplied to the switch 26 after being corrected for the time delay required for signal processing in the error check circuit 31 to the peak detection circuit 33. The switch 26 is set to 0 when an NG signal is supplied from the error check circuit 31 or the peak detection circuit 33.
", and when no NG signal is supplied from either, the output of the delay compensation circuit 34 is output as is.

Therefore, when an NG signal is generated, averaging is not performed, and when an NG signal is not generated, averaging is performed in the averaging circuit 13 so that the peak positions given from the peak detection circuit 33 match. It will be done. Output of the averaging circuit 13.

That is, the result of the addition and averaging is differentiated by the differential filter 14. In addition, as the differential filter 14, for example, [-1,0
, 1] whose center tap is 0 is used. In this way, if it is easier to detect peaks by using a filter with a center tap of 0 when detecting peaks, then if a filter with a center tap of 0 is used for differentiation as well, the peak will appear in the signal after differentiation. Therefore, when trying to control the DC gain of the filter 11 by individually controlling only the center tap of the transversal filter 11 using peak data, the tap gain of the filter 11 does not become a very large value. , it becomes easier to control.

In this case, the reference signal (
Internal reference waveform) is also a step reference signal in the video signal +
Also called "rGCR bar". It is necessary to prepare a waveform obtained by differentiating the original waveform of the signal (which may be a vertical synchronizing signal) using a filter having the same shape as the differential filter 14 described above. Then, the signal differentiated by the differential filter 14 is combined with the pre-calculated reference signal from the reference waveform generation circuit 18 and the X-reducer 1.
Based on this subtraction result (error signal sequence) which is compared (subtracted in this case) in step 5, a predetermined magnification is set in the magnification setting circuit 16, and the weighting setting circuit 17 multiplies the subtraction result by the magnification. The tap gain signal sequence of the transversal filter 11 is determined, and the weighting of each filter constituting the transversal filter 11 is set. As a result, the video signal from which the ghost has been successfully removed is outputted via the line 12. By repeating the operation of 0 or more and sequentially updating the tap gain, the ghost and waveform distortion can be effectively removed. I can do it.

FIG. 10 is a block configuration diagram showing another example of the configuration of the low-band BPF and the peak detection circuit (the peak detection circuit 33 is the same as in FIG. 8); The same reference numerals are given to the constituent parts, and detailed explanation thereof will be omitted.

The captured signal coming from the input terminal 1n7 is sequentially delayed by unit time Ts by each of the unit delay circuits DLI to D[31, and a part of it is inverted by the sign inverters 11 to I16, and then sent to the synthesizer 41. be synthesized. This means that the tap gain is [-1,-1,...,-1,1,1,...,1.1
] (In this example, there are 16 -1s and 16s each). That is, compared to the configuration example shown in FIG. 8, the center tap 0 is eliminated.

The output of the synthesizer 41 (low-pass BPF 32) is supplied to the comparator 37, where the peak search threshold level is stored in the memory 42.

Alternatively, it is compared with the maximum value of the output from the past synthesizer 41 within the peak search period, and the larger one is newly stored in the storage device 42 as the maximum value. When the maximum value is updated in this manner, a write signal is supplied from the comparator 37 to the memory 43 via the OR circuit 46, and the value of the position counter 44 at that time is stored in the memory 43. Memory device 4
3 is latched into the latch circuit 45 at the end of the peak search period.

The position counter 44 is reset at the start of the peak search period, and the count value of the position counter 44 at that time is simultaneously stored in the memory 43. Therefore, the output of the latch circuit 45 becomes a value representing the position of the maximum ri (peak value) of the output of the low-band BPF 32 within the peak search period. Furthermore, if a signal having a level equal to or higher than a preset peak search threshold level does not appear within the peak search period, a value representing the position at the start of the peak search period is output. The output of this latch circuit 45 is
The peak position signal ta> is outputted to the averaging circuit 13 via line i6, and is also supplied to the comparator 38. In this comparator 38, it is compared with the value (b) of the position counter 44 at the start of the peak search period, and a=b
In this case, it is assumed that the predetermined peak did not appear within the peak search period, and the NG signal line 16. OR circuit 35
The signal is output to switch 26 in FIG.

Here, if a peak search filter (corresponding to low-pass BPF 32) is used, for example, with a tap gain of [-1, 1], its frequency characteristic will be within the video band, as shown by curve C in Figure 11. In this case, the frequency characteristics of the filter in this example are similar to those in the figure, and are more susceptible to the effects of noise and ghosts contained in the captured signal, making it easier to falsely detect peaks. Since it is a low-frequency BPF as shown by curve d, it is hardly affected by noise or ghost contained in the captured signal, and stable peak detection can be performed.

The output of the waveform extraction circuit 12 that has undergone necessary delay time correction at the delay compensation port fIB34 is supplied to the switch 6, and when no NG signal is supplied from the error check circuit 31 and the peak detection circuit 33, Delay compensation circuit 3
4 is output as is, and when an NG signal is supplied from at least one of them, "0" is output, so no averaging is performed, and only when an NG signal is not generated, the averaging circuit 13 Addition and averaging is performed while matching the peak positions given from the peak detection circuit 33. The output of the averaging circuit 13, ie, the result of the averaging, is differentiated by a differential filter 14.

In addition, as the differential filter 14, for example, [-1, 1]
As shown in FIG. If it is easier to detect peaks by using a filter in which the left and right coefficients are symmetrical with opposite signs across the unit delay circuit, it is better to use a filter with the same configuration for differentiation. , Since a peak appears in the signal after differentiation, only the center tap of the transversal filter 11 is individually controlled using the peak data, and the filter 11 is
When attempting to control the DC gain of the filter 11, the tap gain of the filter 11 does not become a very large value, making it easier to control (ii).

In this case, the reference signal generated by the reference waveform generation circuit 18 also needs to have a waveform obtained by differentiating the original waveform of the step reference signal in the video signal using a filter having the same shape as the differential filter 14. Then, the signal differentiated by the differential filter 14 is compared (subtracted) with the pre-calculated reference signal from the reference waveform generation circuit 18 in the subtracter 15.
Based on this subtraction result (error signal sequence), a predetermined magnification is set in the magnification setting circuit 16, and the weighting setting port 117 multiplies the subtraction result by the magnification, thereby changing the tap gain signal sequence of the transversal filter 11. is determined, and the weighting of each filter constituting the filter 11 is set. As a result, the video signal from which the ghost has been successfully removed is outputted via the line ε2, and the tap gain is sequentially updated by repeatedly performing an operation of 0 or more, thereby effectively removing the ghost and waveform distortion. I can do it.

In the above description, the reference signal is extracted from the output side of the transversal filter 11 and the tap gain is updated sequentially (i.e., feedback type control).
However, the present invention is not limited to this, and the configuration may be such that the reference signal is extracted from the input side of the filter 11 (i.e., feedforward type control) without using the filter output based on the past tap gain to determine the tap gain. The ghost removal device of the present invention can be applied to any type of control.

〔effect〕

As described above, according to the ghost removal device of the present invention, jitter is removed from the reference signal acquisition pulse by peak matching during addition and averaging in the addition and averaging circuit. Since BPF is used, it is possible to detect the rising (falling) edge of a step without being affected by noise or ghosting, and it is also possible to detect the rising (falling) edge of a step without being affected by noise or ghosting.In addition, it is extremely different from a signal with a normal ghost or when a peak cannot be detected during averaging. When a waveform is detected, by excluding that signal, it is possible to prevent malfunctions in the event of an abnormality.Furthermore, since a peak also appears in the signal after differentiation, only the center tap of the filter can be controlled individually. , when controlling the DC gain of the transversal filter, the tap gain of the transversal filter is not so large,
It has various excellent features such as being able to remove ghosts more smoothly and effectively because rfIIgg is easy to use.

[Brief explanation of drawings]

1 and 2 are block diagrams of a ghost removal device of the present invention and a conventional ghost removal device, respectively. FIG. 3 is a diagram of various signal waveforms of reference waveform generation signals used in the device of the present invention and a conventional device.
The figure is a block diagram showing a specific configuration example of a waveform extraction circuit and an averaging circuit of a conventional ghost removal device.
~(E) are signal waveform diagrams for explaining the averaging operation in the conventional device, FIG. 6 is a signal waveform diagram for explaining the operating principle of error checking and peak detection, and FIG. 7 is a block diagram showing a specific example of the configuration of the error check circuit. 8 and 10 are block diagrams showing specific configuration examples of the low-band BPF and peak detection circuit, and FIGS. 9 and 11 are low-level configuration diagrams of the configurations in FIGS. 8 and 10, respectively. FIG. 2 is a frequency characteristic diagram of a band BPF (peak search filter). 8... A/D converter, 9... Timing signal generation circuit, 10... Ghost removal device, 11... Transversal filter, 12... Waveform extraction circuit, 13...
・Averaging circuit, 14... Differential filter, 15...
Subtractor, 16... Magnification setting circuit, 17... Weighting setting circuit, 18... Reference waveform generation circuit, 22... Addition circuit, 23... Memory device, 24-27... Switch, 31...Error check circuit, 32...Low range BP
F, 33...Peak detection circuit, 34...Delay compensation circuit, 35.46...OR circuit, 36-38...Comparator, 39...79717971 circuit, 40.45...
・Latch circuit, 41...Synthesizer, 42.43...Storage device, 44...Position counter, 0[1 to 0[32...
・Unit delay circuit, ■1 to I16...Sign inverter. Patent applicant: Japan Victor Co., Ltd. Representative: Kunio Kakimoto Ywob] Figure '421

Claims (1)

[Claims] a transversal filter that is configured with an FIR filter or an IIR filter and removes ghost components from an input video signal by setting their tap gains;
A waveform extraction circuit extracts a signal of a predetermined fixed period including a reference signal for ghost detection included in the input video signal;
An averaging circuit that performs averaging to improve /N, a differential filter that differentiates the output signal of the averaging circuit, and a comparison result that compares the output of the differential filter with a preset reference waveform. a subtracter that outputs a corresponding signal, a magnification setting circuit that sets a predetermined magnification based on the result of this comparison, and a weighting (tap gain) that is applied to the transformer by multiplying the output of the subtracter by the predetermined magnification. In a ghost removal device equipped with a weighting setting circuit set in a versatile filter, when a signal with a level different from a preset error threshold is detected between the waveform extraction circuit and the averaging circuit. NG
An error check circuit that generates a signal, a low-range BPF that extracts a peak as a reference position from the signal taken in by the waveform extraction circuit, and a low-range BPF that extracts a peak that is not above a predetermined level. a peak detection circuit that generates an NG signal when the error check circuit and the peak detection circuit output the output signal of the waveform extraction circuit when the NG signal is not generated by the error check circuit and the peak detection circuit; By inserting a switch means that outputs "0" when supplied, the peak positions given from the peak detection circuit are made to match in the averaging circuit only when no NG signal is generated. What is claimed is: 1. A ghost removal device characterized in that the ghost removal device is configured to perform addition and averaging.