JPH0441854B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention extracts a reference signal from a transmitted signal, and controls the tap load amount of a transversal filter based on the comparison result between this reference signal and the transmitted signal. The present invention relates to an automatic equalizer that performs waveform equalization, and particularly relates to an automatic equalizer that prevents abnormal operations such as system divergence and oscillation during waveform automatic equalization.

[Technical background of the invention and its problems]

As an application example of an automatic equalizer that extracts a periodic reference signal from the transmitted signal, compares this reference signal with the transmitted signal, and controls the tap load amount of the transversal filter to perform waveform equalization,
Ghost removal devices for television receivers are known (Reference: Murakami et al., ``Digital Automatic Ghost Elimination Device'', Institute of Electronics and Communication Engineers Technical Research Report EMCJ78-37, November 1978).

FIG. 1 shows a circuit diagram of an example in which a conventional automatic equalizer is applied to a ghost removal device for a television receiver.

In Figure 1, the input video signal is input to input terminal 1.
0, and each tap delay element 21 is applied to a tap gain variable transversal filter 20.
The signal whose waveform has been equalized by controlling the amount of load applied to the load circuit 22 provided in the adder 23
get to.

Delay time between each tap of tap delay element 21
T ₁ is set to satisfy the Nyquist interval, and is selected to be smaller than the reciprocal of twice the highest frequency of the input video signal, for example 0.1 μS. The total number of taps 22 is determined according to the setting of the delay or advance time width of the ghost to be erased. For example, if the total number of taps is 100, ghost signals occurring in a time width of 10 μS can be removed.

The weight circuit 22 provided in each tap 22 is a multiplication circuit that weights the corresponding delayed signal by a predetermined amount of weight, and the amount of weight is called a tap gain. Here, the tap gain for the main tap is C _p , the tap gain for the front ghost is C _-M ~ _{C -1} , and the tap gain for the rear ghost is C p .
It is expressed as C ₁ −C _N.

By appropriately controlling the tap gain {C _i } (the sequence of C _{- M} to C _p to C _N is expressed as Ci) of the transversal filter 20 having the tap 22, the ghost signal at the input terminal 10 can be suppressed. The ingredients are
At the output of the adder 23 of the transversal filter 20 it is substantially cancelled. Adder 2 above
The output of No. 3 is applied to a signal switch 50, and an equalized signal with ghost signals eliminated is obtained at the output terminal 30.

Waveform equalization for this ghost signal is performed by controlling the tap gain of the tap 22, but algorithms for controlling the tap gain so that the ghost signal component is minimized include the following least squares method, zero Examples include the forcing method.

To describe the waveform equalization effect, first, from the input video signal applied from the input terminal 10, under the control of the timing control circuit 44, a predetermined length of the leading edge of the vertical synchronization pulse to be focused on as a reference signal is separated. , this is passed through the differentiating circuit 40 to the input waveform {Xk}
It is stored in the input waveform memory 41 as a. On the other hand, the video signal related to the output of the transversal filter 20 at the same time is extracted, passes through the differentiation circuit 42 and the reference waveform subtraction circuit 43, and then is stored in the error signal memory 46 as an error signal {ek}. The error signal {ek} is sent to the timing circuit 44.
The reference waveform subtraction circuit 43 calculates the difference between the reference waveform {rk} obtained as the output of the reference waveform generation circuit 45 under the control of the reference waveform generating circuit 45 and the output signal {yk} of the differentiating circuit 42.

The input waveform memory 41 and the error signal memory 46
The input waveform {xk} and the error signal {ek}, which are sample value series stored in the timing circuit 44
αi= _Q 〓 ^K=P xk−i
The correlation calculation ek...(1) is performed. Here, in the above, the correlation calculation range [P, Q] is usually
Take P=2M and Q=2N. The correlation calculation result according to equation (1) indicates the approximate magnitude of the ghost signal component detected at the i-th tap 22.

The correlation calculation results obtained in this way are stored in the tap gain memory 48 corresponding to each tap, and the initial values are Co=1, C-n to C-1=o,
C ₁ to C _N =o.

Each time the calculation of the above equation (1) is completed for one of i=-M to N, the tap gain memory 48
The tap gain ei is read out from the tap gain memory 48, and the tap gain memory 48 is written after the correction expressed as Ci, new=Ci, old-αdi...(2) (α is a small positive value). The calculations according to the above equations (1) and (2) are performed by the tap gain correction calculation circuit 47 for all i during one field.

These calculations are repeated, for example, each time a new reference waveform is received (ie, once per field).

According to the above calculation, the gain for the tap 22 is repeatedly modified, the output waveform {yk} approaches the reference waveform {rk}, and the error signal {ek} finally converges to a predetermined value.

At this time, the output waveform {yk} minimizes the residual error defined by E= _Q 〓 ^K=P (yk−rk) ² (3), so it is called the least squares method.

According to the algorithm according to the above equations (1) and (2), the tap gain value {Ci} converges to a predetermined value in principle, but in reality the frequency characteristics of the transversal filter 20 are not ideal. Therefore, the tap gain does not necessarily converge to a constant value. After starting the sequential correction control for the tap gain, the tap gain value changes toward a predetermined amount until a certain time at the beginning.
As time passes, the tap gain {Ci} gradually diverges, and the automatic equalizer may malfunction. In particular, if the transversal filter 20 is connected in a feedback manner, the output signal will be in an oscillating state, which may cause the automatic equalizer to malfunction.

Also, instead of using the least squares method for the tap gain correction algorithm, instead of using the above equations (1) and (2), the tap gain can be calculated using Ci, new = Ci, old − αei... (4). Even in the case of correction using so-called zero focusing, the automatic equalization effect due to oscillation etc. will be abnormal, as in the case of using the least squares method.

In order to deal with these abnormal operations, conventionally, as shown in FIG. 1, an abnormal operation detection circuit 60 is provided on the output side of the transversal filter 20, and when the automatic equalization function becomes abnormal due to oscillation or the like, This is detected by the abnormal operation detection circuit 60. The detection result of the abnormal operation detection circuit 60 controls the signal switch 50, and when an abnormal state is detected, the output terminal 30 is switched from the terminal 50 to the terminal 51.
At this time, the video signal applied to the input terminal 10 is directly led out to the output terminal 30, and the waveform equalization operation is stopped.

Here, the abnormal operation detection circuit 60 is composed of a level detection circuit 61 and a level judgment circuit 62, and in consideration of the fact that the output voltage of the transversal filter 20 fluctuates when there is an abnormality in the automatic equalization function, a transversal operation detection circuit 60 is constructed. A level detection circuit 61 detects a level change in the DC voltage level of the adder 11 of the filter 20, and a level determination circuit 62 determines the detected DC voltage level to generate a control signal for the signal cutter 50. . (Such an abnormal operation detection method is described in Japanese Patent Application Laid-Open No. 56-69973, for example.
It is described in the publication No. ``Television Ghost Removal Device''. ) In the above-described conventional automatic equalizer, since the output of the adder 11 of the transversal filter 20 is detected, the detection sensitivity for abnormal operation detection is poor, resulting in a problem that detection of abnormal operation is delayed. For this reason, the distortion in the output of the transversal filter may become larger than the distortion in the input signal due to the phase fluctuation of the ghost, and the automatic waveform equalization becomes unstable, resulting in the distorted signal being output as is. In other words, the input distorted signal is further distorted and output as is.

[Purpose of the invention]

In view of the above points, this invention appropriately detects abnormal operations such as system divergence and oscillation in an automatic equalizer, and immediately detects when output distortion becomes larger than input distortion. An object of the present invention is to provide an automatic equalizer that can prevent an excessively distorted signal from being derived on the output side.

[Summary of the invention]

In this invention, the distortion on the input end side and the distortion on the output end side of the automatic equalizer are detected, and based on the detection results, it is detected that the output side distortion has become relatively large with respect to the input side, Corresponding to the detection result, the tap gain correction operation is controlled to prevent the system from becoming unstable.

This prevents the system from diverging.

[Embodiments of the invention]

Embodiments of the automatic equalizer according to the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the automatic equalizer according to the present invention, and parts corresponding to those shown in FIG.

In FIG. 2, the gain control itself for the tap 22 is controlled by the same means as the automatic equalizer described in FIG. This is different from the conventional automatic equalizer shown in FIG.

Therefore, abnormal operation detection means for the automatic equalizer shown in FIG. 2 will be described. In the automatic equalizer shown in FIG. 2, abnormal operation is detected by sequentially comparing the input waveform {xk} and the output waveform {yk}. That is, the comparison circuit 70 uses a sample value sequence {xk} having a predetermined length of the leading edge of the pulse of the vertical synchronization signal in the input signal, and the transversal filter 2.
A comparator circuit 70 compares both sample value series {yk} for a predetermined length portion of the leading edge of a pulse in a vertical synchronization signal in an output signal of zero.

Here, if we evaluate the amount of waveform distortion in detail, for example, by the sum of the absolute values of the sample value series, the amount of waveform distortion of the input signal is _K1 〓 ⁱ⁼⁰ , where the number of samples in the sample value series is k ₁ .
It is represented by |xi|, and the amount of waveform distortion of the output signal of the transversal filter is represented by _K1 〓 ⁱ⁼⁰ |yi|.

The comparison circuit 70 performs subtraction expressed by the following equation with respect to the amount of waveform distortion of the input/output signal.

U ₁ = _K1 〓 ⁱ⁼⁰ ｜xi｜− _K1 〓 ⁱ⁼⁰ ｜yi｜+A ₁ ...(5) Here, the constant A ₁ is an offset value for the S/N of the signal and the amount of distortion of the input and output signals. is the distortion amount threshold. That is, only in the subtraction part of the above equation (5),
Since the sign of the calculation result changes sharply, a predetermined insensitive area is provided with a threshold value that is determined around _A1 . In other words, a constant A ₁ is added to _K1 〓 ⁱ⁼⁰ |xi| and _K1 〓 ⁱ⁼⁰ |yi| in order to suppress the influence of noise etc. and make the difference result between the two significant. .

The output of the comparison circuit 70 is supplied to a determination circuit 71 that generates a control signal for the signal switch 50. If the value U ₁ in equation (5) above becomes negative, this indicates that the distortion of the input signal is smaller than the distortion of the output signal, and the transversal filter is not functioning as an automatic equalizer. The equalizer is in an abnormal state. At this time, a control signal for connecting the output terminal 30 and the terminal 51 is output from the determination circuit 71 to the signal switch 50.

On the contrary, if the calculation result U ₁ according to the above equation (5) is a positive value or zero, the distortion of the output of the transversal filter 20 is smaller than the distortion on the input side, and the automatic The equalizer is performing equalization normally, and the determination circuit 71 determines that the automatic equalizer is normal, and connects the output terminal 30 to the output terminal of the transversal filter 20 to the signal switch 50. 52 side and continue automatic equalization operation.

Since the input waveform and the output waveform are sequentially compared in this way, it is possible to determine an abnormality in the system with a predetermined sensitivity. Note that the sensitivity of abnormality detection is based on item (5) above.
It can be adjusted by selecting the value of the constant term A ₁ in the equation. In this way, the magnitude of the input waveform and the waveform after waveform equalization are compared, and if the output waveform is larger as a result of the comparison, it is determined that the system related to automatic waveform equalization is unstable and automatic The equalization operation is stopped, the signal switch 50 is connected to the terminal 51 side, and the original signal without waveform equalization is directly outputted to the output terminal 30. In other words, if it is determined that the automatic equalization system is unstable, the original signal is delivered to the output terminal without performing the waveform equalization operation, thereby preventing an unstable signal from being delivered.

FIG. 3 is a circuit diagram showing details of the comparison circuit 70 and determination circuit 71 in FIG.
5. Adder 106, distortion amount threshold generation circuit 108
The output end of the adder 106 is connected to a positive/negative determining circuit 107 forming the determining circuit 71, and its output is led out to a terminal 109.

The comparison circuit 70 and determination circuit 71 configured in this way perform the calculation shown in the above equation (5). First, a signal obtained by differentiating the original signal by the differentiating circuit 40 is applied to the input terminal 100 of the comparing circuit 70, and _K1 〓 ⁱ⁼⁰ |xi| is determined for the input waveform by the adder/subtractor 101 and the shift register 102. The value is latched into latch circuit 104 via latch circuit 103. Next, in the same manner, the output of the transversal filter 20 is connected to the terminal 100 by the differentiating circuit 42.
When the signal differentiated by is added, the adder/subtractor 10
1 and the shift register 102, _K1 〓 ⁱ⁼⁰ |yi| is determined and latched by the latch circuit 103. Here, the value _K1 latched in the latch circuit 104 〓 ⁱ⁼⁰
|xi| and the value latched in the latch 103 above
Subtraction with _K1 〓 ⁱ⁼⁰ |yi| is performed by the subtractor 105 to obtain the value of _K1 〓 ⁱ⁼⁰ |xi|− _K1 〓 ⁱ⁼⁰ |yi|. Next, the value A ₁ generated by the distortion amount threshold generation circuit 108 is added to this value, and the value of U ₁ shown in the above equation (5) is obtained as the output of the above adder 106. The result of this calculation is output to the output terminal 109 of the determination circuit 71, and the switching of the signal switch 50 is controlled by this output.

FIG. 4 is a circuit diagram showing another embodiment of the present invention, in which the automatic waveform equalization itself is performed according to an algorithm according to equations (3) and (4) above. Further, in the same figure, the comparator 70 compares the magnitude of the distortion amount between the input terminal 10 side and the output terminal 30 side by calculation according to the above equation (5).

If the value U ₁ as a result of the comparison operation based on equation (5) is positive or zero, the next-stage determination circuit 72 determines that the automatic waveform equalization operation is normal, and the connection terminals 74 and 75 of the switch 73 are connected to terminals 76 and 78, respectively. That is, when the output of the comparison circuit 70 is positive or zero, the above-mentioned equation (8) or (4)
Waveform equalization is performed by a conventional algorithm according to the formula:

On the other hand, when the amount of distortion on the output side becomes larger than the amount of distortion on the input side, and the output of the comparison circuit 70 becomes a negative value, the determination circuit 72 performs tap gain correction calculation with leakage. This prevents divergence of the system. That is, when the system becomes unstable, the tap gain modification calculation circuit 47 does not perform the tap gain modification algorithm, but the tap gain modification calculation circuit 80 with leakage performs the calculation for tap gain modification.

When it is detected that the system is unstable, the leakage tap gain correction calculation circuit 80 uses Ci,new=(1-β)ei,old-instead of the algorithm shown in equation (2) above. αdi(i≠o) Co,new=1+(1−β)(Do,old−1)αdo ……(7) Ci,new=Ci,old−l.SgnCi,old−αdo(i≠o
) Ci, new=Ci, old−l.SgnCi, old−αdo(i≠o
) Co, new=Co, old−l.Sgn(Co, old−1)−αdo……(8
), there is a slight leak in the tap gain correction control (the first
Tap gain correction calculation with leakage is performed by adding β in equation (7) or l) shown in equation (8). In this case, when modifying the tap gain, the basic idea of determining the new modification amount using the previous modification amount is the same as the above equation (2), but the above equations (7), (8), etc. The tap gain correction with leak shown by is different from the tap gain correction according to equation (2) in that when determining new correction data, the new correction data is determined by multiplying the previous data by a predetermined attenuation coefficient. . Leak coefficient β, l shown in equations (7) and (8) above
When is increased, the increase in tap gain {Ci} is suppressed, and the increase in correction amount {Ci) is suppressed. In the case of equation (8), compared to the case of proportional control shown in equation (7), the correction amount is suppressed discretely, and the correction operation is prevented from being carried out too sensitively. Ru.

As described above, in the embodiment shown in FIG. 4, the comparator circuit 70 and the determination circuit 72 detect that the system has become unstable and replace the tap gain correction computation with the tap gain modifying computation with leakage. This suppresses the change in tap correction amount and prevents the system from divergence.

Although an example has been described in which tap gain correction with leakage is performed to prevent system divergence, the above judgment circuit 72
If it is detected that the system is unstable, the tap gain correction calculation operation may be stopped.

The embodiment shown in FIG. 5 determines whether or not the system is unstable by determining the amount of waveform distortion for the sample value series {yk} of the output signal on the output terminal 30 side in time series, and calculating the amount of distortion. This is done by comparing with a predetermined constant value, and the determination circuit 71 is controlled by the output.

That is, when the comparison circuit 81 generates a determination signal indicating that the system is unstable, the determination circuit 71 switches the signal switch 50 and outputs the input original signal without automatic equalization to the output terminal 30. Now, to explain the operation of the comparison circuit 81 in the next series, first let Y be the amount of waveform distortion on the output end side in the first field diagram immediately after the start of the waveform equivalent operation. In the first field immediately after the waveform equalization operation, the tap gain correction operation is not yet performed, and the input signal appears as it is at the output end. If the distortion appearing at each tap of the transversal filter 20 in the first field is Yi, 1, the sum of its absolute values Y is expressed as Y= _K1 〓 ⁱ⁼⁰ | yi, ₁ |...(9) .

Also, for the fields after the first field, using the sum of the absolute values of the sample value series,
It is shown by the following formula.

U ₂ =Y− _K1 〓 ⁱ⁼⁰ |yi, l|+A ₂ ...(10) Calculate the quantity U ₂ (l=2, 3, 4...). (Note that A ₂ corresponds to the distortion amount threshold described above.) This calculation is performed in the comparator circuit 81, and if the calculation result U ₂ is positive or zero, it is determined that the system is unstable. is detected, in this case, the determination circuit 72 switches the switch 73 to
The aforementioned tap gain correction with leakage is performed on the transversal filter to suppress an increase in tap gain and stabilize the system. Also, the above calculation result
When U ₂ is U ₂ >0, normal tap gain correction is performed. In this way, the system is stabilized by the equation following equation (10) above, but _K1 〓 ⁱ⁼⁰ |yi, n| in the nth field after the start of the automatic equalization operation becomes Using this value as a reference, compare it with the m (m>n) sample value series _K1 〓 ⁱ⁼⁰ |yi, m| from the n-th field onwards, and calculate U ₃ = _K1 〓 ⁱ⁼⁰ |yi, The switch 48 may be controlled based on the calculation result n| _−K1 〓 ⁱ⁼⁰ |yi, m|+A ₃ (11). In this case, the first term on the right side of Equation 11 is the sum of the output sample value series when the ghost disappears to some extent, so when applying the initial value in Equation (10) above as the reference value, Appropriate in comparison.

Furthermore, in equation (11), if the parameter n of the first item on the right-hand side is not a fixed value but a variable parameter, this first item can always be set as a reference value at a value with less variation that reduces distortion. . In this way, since the stability of the system is determined based on a value with a small amount of variation, it is possible to prevent the automatic equalization from intermittent even though the system is unstable, thereby promoting instability of the system.

〔Effect of the invention〕

As described above, according to the present invention, conditions leading to system instability are properly detected, and the automatic equalization is stopped or the tap gain correction is controlled in accordance with the detection result. It is possible to provide an automatic equalizer that stably performs automatic waveform equalization.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional automatic equalizer, Figure 2 is a circuit diagram showing a conventional automatic equalizer.
The figure is a circuit diagram showing one embodiment of an automatic equalizer according to the present invention, FIG. 3 is a circuit diagram showing a part of the circuit of FIG. 2 in detail, and FIGS. It is a circuit diagram showing an example of. 10...Input terminal, 11...Adder, 20...
Transversal filter, 30...output terminal,
70, 72, 73, 80, 81...Tap gain correction control means.

Claims (1)

[Claims] 1. A reference signal corresponding to the reference signal is extracted from a transmission input signal containing a reference signal of a predetermined period applied to an input terminal, and a distorted signal that has undergone transmission distortion corresponding to this reference signal is extracted. and means for generating an error signal by detecting an error between the tap and the tap by a predetermined calculation, and a transversal device in which the tap load amount is controlled at every predetermined delay time by a tap gain correction calculation according to a predetermined algorithm according to the error signal. a filter; an adder having an output terminal that adds the tap outputs of the transversal filter and outputs a signal whose waveform is equalized with respect to the transmission signal applied to the input terminal; and distortion on the input terminal side. a detection means for detecting that the system is unstable due to an increase in the amount of distortion on the output terminal side relative to the amount of distortion; Sometimes, the tap gain modification algorithm is changed to suppress the tap gain modification operation, or a signal is derived that does not perform waveform equalization on the input signal, regardless of the system state. An automatic equalizer comprising at least tap gain correction control means for preventing unstable signals from being derived at the output terminal.