JPH01300706A - Waveform equalization circuit - Google Patents

Abstract

PURPOSE:To improve the utilizing efficiency of an A/d converter circuit and to eliminate ghosts by controlling the operations of an amplitude adjusting means and reference signal adjusting means based on operated results of a tap gain in the vicinity of the main tap of a transversal filter. CONSTITUTION:The tap gain of the transversal filter 15 is calculated by a tap gain control circuit 17 and inputted through a tap gain memory 16. When the operated quantity of the gain of a tap in the vicinity of the main tap is larger than a certain set value G1 at the time of operated the tap gain of the filter 15, an attenuator (ATT) 13 is adjusting by an ATT control circuit 18 so that the amplitude of input signals can become smaller. When a positive ghost is added, the amplitude of the input ATT 13 is not narrowed since the ghost may not become a beard-like shape and may not remain after erasure. However, when the main tap rises larger and the ghost equalizing capacity is dropped, the rise of the main tap is made smaller so as to prevent the drop of the ghost equalizing capacity by making a reference signal smaller by means of a reference signal control circuit 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a waveform equalization circuit that automatically equalizes the waveform of a received signal such as a teletext signal.

(Prior Art) In complex signal transmission circuits, attenuation distortion occurs within the signal transmission band, and a waveform equalization circuit is often added to compensate for this.

In general, time-invariant distortions are equalized by a fixed attenuation equalization circuit, but particularly complex forms of distortion are equalized by a variable attenuation equalization circuit.

Furthermore, in transmission circuits for data codes, broadcast signals, etc., variable delay equalization circuits are often used to linearize phase characteristics (keep delay characteristics constant).

There is a type of variable delay equalization circuit called a cosine type. For example, when the signal transmission band is 0 to f, the main signal Co f (t) is passed through a transversal filter with taps for each constant delay τ0 (≦1/2f) and taken out from the center of the l-1 line. and a signal that is temporally advanced and delayed by τ0 is added to the output signal.

FIG. 6 is a diagram showing an example of the configuration of a waveform equalization circuit using a transversal filter.

In the figure, 1 is an input terminal into which a signal is input, 2 is an AGC amplifier that adjusts the gain of the input signal, 3 is an A/D conversion circuit that converts the input signal into a digital signal, and 4 is equipped with a tap for each fixed delay. 5 is a tap gain memory that stores a value indicating the gain of each tap;
6 is a tap gain control circuit that writes a value into this tap gain memory, and 7 is an output terminal from which a signal is output.

First, the received signal applied to input terminal 1 is AGC amplifier 2
By passing through the A/
The D conversion circuit 3 converts it into a digital signal.

The received signal converted into a digital signal is subjected to a waveform equalization effect in a transversal filter 4 and is taken out from an output terminal 7. The gain of each tap of the transversal filter 4 is supplied from the tap gain memory 5, and the gain value is determined in the tap gain control circuit 6 based on the difference between the input signal of the transversal filter 4 and the corresponding output signal. is calculated.

By the way, in this type of waveform equalization circuit, when the level fluctuation of the received signal is relatively gentle and can be compensated for by the AGC amplifier 2, waveform equalization is performed completely, but if the level fluctuation of the received signal is If a large negative ghost is added, the dynamic range of the A/D conversion circuit 3 is exceeded, and waveform equalization may not be performed completely.

FIG. 7 is a diagram explaining this.

In the figure, (a) shows a state in which there is no ghost, (b) shows a state in which a negative ghost is added, and (C) shows a state in which a positive ghost is added.

First, as shown in FIG. 2(b), when a negative ghost is added to the human input signal, A
Since the operation of the GC amplifier 2 cannot follow the operation, the input to the A/D conversion circuit 3 becomes excessive and exceeds the dynamic range B. Then, the information on the whisker-like portion H is transmitted to the transversal filter without being transmitted, so this portion is not waveform-equalized.

In addition, to prevent this, the input of the A/D conversion circuit 3 must be adjusted so that it does not exceed the dynamic range B even if there is a large negative ghost.
The overall input signal becomes too small.

In addition, all the taps of the transversal filter are turned on to perform amplification operation in order to adjust the excessive input signal to the magnitude of the reference signal, making it impossible to fully utilize the equalization ability.

Furthermore, as shown in FIG. 7(c), if a large positive ghost is added, the AGC amplifier 2 sets the value to A, but if the reference signal of the transversal filter is constant, the main tap The tap gain for ghost removal increases, and the tap gain for ghost removal also increases, leaving some ghosts to disappear.

(Problems to be Solved by the Invention) As described above, in the conventional waveform equalization circuit, the usage efficiency of the A/D conversion circuit is low, and the equalization ability of the transversal filter cannot be fully utilized. There was a problem that sometimes occurred.

The present invention was made in view of the above circumstances, and it is an object of the present invention to increase the usage efficiency of an A/D conversion circuit in a waveform equalization circuit.
The purpose is to make full use of the equalization ability of the transversal filter and eliminate the possibility that ghosts remain undisappeared.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve this object, the waveform equalization circuit of the present invention includes an amplitude adjustment means for adjusting the amplitude of a received signal, and a digital converter for the amplitude-adjusted signal. a conversion means for converting into a value, a reference signal adjustment means for adjusting the magnitude of the reference signal in the transversal filter, an amplitude adjustment means and a reference signal adjustment based on the calculation result of the tap gain near the main tap of the transversal filter. and control means for controlling the operation of the means.

(Function) In the waveform equalization circuit of the present invention, when a negative ghost exists, the amplitude of the input signal is reduced so as not to saturate the A/D conversion circuit, but later when the amplitude of the human input signal becomes small, returns the input amplitude to its original value and reduces the gain of the main tap. This can also eliminate large ghosts.

Furthermore, when a positive ghost exists, the tap gain of the main tap is suppressed by reducing the reference signal in the transversal filter.

When a positive ghost exists, the value of the amplitude adjustment means is fixed because the input signal does not remain in the form of a thin whisker as in the case of a negative ghost.

In a transversal filter, the output signal is adjusted to have the magnitude of the reference signal in the filter, so if the amplitude of the human input signal is smaller than the amplitude of the reference signal, the tap gain will be high even if there is no ghost.

For this reason, the - part of the tap gain variation width of the filter is used to amplify the input signal, and the tap gain used for ghost equalization is reduced, resulting in a decrease in equalization ability.

In the present invention, when adding a positive ghost, if the tap gain of the main tap exceeds a certain set value, the magnitude of the reference signal is reduced,
This prevents the tap gain from becoming unnecessarily large and allows the tap gain to be effectively used for ghost equalization.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

In the figure, 11 is an input terminal into which a signal is input, 12 is an AGC amplifier that adjusts the gain of the input signal, and 13 is an attenuator (hereinafter referred to as ATT) that adjusts the amplitude of the input signal.
, 14 is an A/D conversion circuit for converting a human input signal into a digital signal, and 15 is a transversal filter having taps for each fixed delay.

Further, 16 is a tap gain memory that stores a value indicating the tap gain of the transversal filter 15, 17 is a tap gain control circuit that writes a value into the tap gain memory 16, and 18
is an ATT control circuit that controls the operation of ATTlB, 19
2 is a reference signal control circuit that adjusts the reference signal within the transversal filter 15, and 20 is an output terminal from which the signal is output.

First, the received signal is input to the input terminal 11, relatively gentle amplitude fluctuations are removed by the AGC amplifier 12, and the amplitude is further finely adjusted by the variable ATT 13.

The received signal is converted into a digital signal by an A/D conversion circuit 14, and then applied to a transversal filter 15 for waveform equalization.

The tap gain of the transversal filter 15 is calculated by the tap gain control circuit 17, and the tap gain of the transversal filter 15 is calculated by the tap gain control circuit 17.
It is input via 6.

At this time, if the amount of calculation of the gain of the tap near the main tap is larger than a certain set value G1, the ATT control circuit 18 adjusts ATT1B so that the amplitude of the human input signal becomes smaller, and the dynamic It will fit within the range.

In this case, since the tap gain near the main tap becomes small, the ghost equalization ability becomes the capacity of the transversal filter 15.

Furthermore, in this state, if the input signal becomes small (and the tap gain of the main tap increases and exceeds the set value G2), the ATT
The control circuit 18 should restore the magnitude of the input signal (ATT
Run l3.

Next, there is a case where a positive ghost is added, but in this case, the ghost does not become whisker-like, so there is no possibility that it remains and the amplitude of the input ATT 1 B is not reduced. However, if the reference signal in the transversal filter 15 is the same as when it is a negative ghost, the input signal will be smaller than the reference signal, so the main tap will be large and the ghost equalization ability will be reduced.

For this reason, in this embodiment, the reference signal is made small by the reference signal control circuit 19, and the rise of the main tap is made small to prevent the ghost equalization ability from deteriorating.

Note that the ATT control circuit 18 and the reference signal control circuit 19 do not operate independently, but when one operates, the other is fixed until the tap gain is stabilized.

The operation of each of the ATT control circuit 18 and the reference signal control circuit 19 to reduce the ATT value and the amplitude of the reference signal is prohibited because the efficiency is low and the switching may become oscillatory.

An example of one ATT control circuit 18 and one reference signal control circuit is shown in FIG.

In the figure, 204 is a comparator, which calculates the amount of calculation for the gain CO of the main tap applied to the input terminal 201 and the input terminal 204.
2. Comparison is made with the comparison reference values A1 and A2 added to 203, and the result is sent to the flip-flop circuit 205.
Output to.

In response to the signal from the comparator 204, the flip-flop circuit 205 outputs an amplitude switching signal for the ATT and reference signals from output terminals 207 and 208.

Further, 206 is a counter circuit, which is operated by the V signal from the input terminal 209 and the signal from the flip-flop circuit 205.

When the output of the flip-flop circuit 205 is switched, the counter circuit 206 counts the V signal until it reaches a predetermined value, and during that time, the amplitude of the input signal and the amplitude of the reference signal of the transversal filter 15 are not changed. That's what I do. This prevents the amplitude of the input signal and the reference signal switching signal of the transversal filter 15 from becoming unstable.

If the comparison reference values A, A2 are inappropriate, the amplitude value of the input signal will change due to, for example, a negative ghost, and when the input signal is narrowed down, the gain of the main tap CO will increase, causing the amplitude value of the input signal to change from the original value. You will end up in a state of vibration that will bring you back to . In order to avoid this situation, the comparison standard value A,...
A2 must satisfy the following conditions.

The tap gain when a negative ghost is added is Co
, ATTl3 gain is G (G<1), then ATT
The tap ill gain Co' at 'J3'0 when l3 is switched is Co'-Co/G.

In this case, in order to prevent vibration, A2
>Co', that is, A2>Co/G. Here, A1>Co, so A'2>A, /G
...The condition (1) must be met. In this case), the magnitude of the signal R is set to 1 at t4.

Next, consider the case where a positive ghost is added.

For this A1 case, the comparison standard values are B, B2. Considering that the magnitude of the reference signal is changed to γ by 1 when the tap gain Co'' when adding a positive ghost is B1 or more, A
When switching TT 1 B, the tap value [Co''' is CO''・γ, and in order to prevent the reference value B2 on the F side from causing vibration, B2<Co''', that is, B2< Must be Ca2 ・γ, CO″〉B1
Therefore, B2 <B,・γ ・・・・・・(2
) conditions must be met.

Further, in the state A2, the tap gain is increased because ATT13 is switched in the negative ghost state, and the increase value B1 of the tap gain in the positive ghost state must be BT>A2. Similarly, since the value of B2 is the tap gain reduced due to switching of the reference signal, A must be <82 in order to discriminate a negative ghost. That is, Bl > A2, B2 > A, 4...
...It is necessary to satisfy the condition (3).

For example, considering the case of G-172 and γ-1/2, (
From equations 1), (2), and (3), B1>A2>A1/G.

B1 ・γ>B;+>Al ・・・・・・(4
) Also, B1>A2>2A+ B1/'2>82>A.

It is.

As an example, if the level at which a negative ghost is determined is 0.5 and the level at which a positive ghost is determined is 2.0, then (4)
The formula can be satisfied. The tap gain here and when there is no ghost is 1.0.

Incidentally, in the embodiments described above, the amplitude of the input signal and the reference signal of the transversal filter are all switched by hardware, but this switching can also be done by software. Figure 3 shows its configuration.

In the figure, 51 is an input terminal, and 52 is an ATT.

53 is an A/D conversion circuit, 54 is a pass line, 55 is a transversal filter, and 56 is a microcomputer section.

First, a signal applied to the input terminal 51 passes through the ATT 52 and is converted into a digital signal by the A/D conversion circuit 53.

This converted signal is sent to the pass line 54,
The signal is supplied to a transversal filter 55 and a microcomputer section 56. Microcomputer section 56
monitors the tap gain signal 57 from the transversal filter 55, thereby determining positive and negative ghosts and their magnitude.

When a positive ghost is determined, the reference switching signal 58 is activated, and when a negative ghost is determined, the ATT switching signal 59 is activated. The algorithm for determining the positive and negative ghosts and for switching between the two switching signals is as shown in FIG. 4, for example.

When the operation is first started, the amplitude of the input signal is set to ATT-1 and the reference signal value is set to R-1 (steps 101 and 102).

Then, in order to determine whether the ghost is positive or negative, the value of the gain Co of the main tap is determined. If the gain Co of the main tap becomes larger than the set value α1, it is determined that there is a large negative ghost, and the settings are reset to ATT-G and R-1 (step 104).

Then, the main tap gain Co up to that point becomes Co', so the human input signal is attenuated by the ATT before being input to the A/D.
It will enter the conversion circuit 53.

As a result, the input signal including the whisker-like portion of the negative ghost falls within the dynamic range of the A/D conversion circuit 53, and no ghost remains.

Next, in this state, if the tap gain Co' becomes large in the positive direction, this means that the amplitude attenuation of the input signal is too large for the input signal at that time, so the tap gain The tap gain is compared with a certain set value β (step 106), and if the tap gain is larger than the set value β, the process returns to step 102 and the ATT 52 is set to G.
→ Return to 1 and increase the input amplitude to the A/D conversion circuit 53.

In this case, after switching ATTl3 from 1 to G, a routine is inserted to wait for a certain period of time to not switch ATTl3 until the tap gain is stabilized (step 105).

In addition, in this series of operations, it is necessary to determine the set values α and β so that the switching of the amplitude of the input signal does not become oscillatory.

This will be explained below with reference to FIG.

First, from the above-mentioned conditions, Co<α1, and by this operation, CO becomes Co −+Co ′ −Co /G.

At this time, if Co' increases in the positive direction and the amplitude of the input signal returns to its original value, Co' becomes Co with a certain width β1.
The amplitude of the human input signal is prevented from returning to its original level unless it becomes larger than /G by β1 or more.

That is, the amplitude of the input signal is set to G-1 only when Co'>Co/G+β1. Therefore, Co/G+β1>
It is necessary to set Co>Co/G.

Next, let's consider positive ghosts. In the case of a positive ghost,
The starting condition is step 102 as in the case of negative ghost.
ATT-1, R-1.

When the tap gain Co'' becomes larger than β2, the reference signal R of the transversal filter is changed from 1 to γ (step 107).Then, the tap gain becomes Co'' - γCo
”.

If the tap gain becomes negative at this time, it means that the reference signal value has been made too large.
Perform the operation to restore the reference signal value to its original value.

In this case as well, for the same reason as in the case of a negative ghost, a routine is inserted to wait for a certain period of time to pass (step 108). The condition for returning the reference signal value to the original value is Co″′−γCo″−β3. Note that β3 is a width that provides hysteresis. In a series of operations corresponding to this positive ghost, β2〉γCO″ 纏γβ2〉γCO″ −β3 −γβ2−β3 β2 is the value of Co′ when returning from step 10G to step 102 when there is a negative ghost, i.e. Go+β
Since it has to be larger than 1G, Co + β1G × β2 Conversely, when returning R to γ-1, the amplitude of the input signal needs to be smaller than when F>G, so -γβ2 - β
3 α, /G.

In this embodiment as well, the magnitude of the input signal to the A/D conversion circuit and the reference signal of the transversal filter is changed by looking at the tap gain of the tap near the main tap, so the equalization performance of the transversal filter is always improved. can be made into an equalization ability determined by the number of bits configuring the transversal filter, which is highly efficient.

In addition, since the switching operation between the ATT switching signal and the reference signal in the transversal filter occurs only at fixed time intervals, the tap gain of the equalization circuit is stabilized during that time, and the amplitude of the input signal is And the transversal filter reference signal does not fluctuate.

[Effects of the Invention] As explained above, the waveform equalization circuit of the present invention adjusts the amplitude of the input signal to the A/D converter by the amount of calculation of the tap gain near the main tap of the transversal filter of the equalization circuit. and a means for switching the magnitude of the reference signal in the transversal filter depending on the magnitude of the tap gain near the main tap, the A/D conversion circuit is used efficiently and the equalization ability of the transversal filter is improved. can be fully utilized, and there is no risk of ghosts remaining undisappeared.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG.
A diagram showing an example of a TT control circuit and a reference signal control circuit,
Fig. 3 is a diagram showing an example in which switching of ATT and reference values is performed by software, Fig. 4 is a diagram showing an example of an algorithm for determining positive and negative ghosts, and switching of ATT and reference values. Figure 6 shows an example of the configuration of a conventional waveform equalization circuit.
The figure is a diagram illustrating a case where a ghost is added to a received signal. 12...AGC amplifier, 13...ATT, 14...
- A/D conversion circuit, 15... Transversal filter, 16... Tap gain memory, 17... Tap gain control circuit, 18... ATT control circuit, 19... Reference signal control circuit. Applicant Toshiba Corporation Patent Attorney Sasa Suyama - Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) A received signal is input to a transversal filter with a variable tap gain, and the tap gain of the transversal filter is adjusted so that an output signal corresponding to a predetermined waveform in the received signal approximates a predetermined reference signal. A waveform equalization circuit that equalizes the waveform of the received signal by modifying the received signal, comprising: amplitude adjustment means for adjusting the amplitude of the received signal; conversion means for converting the amplitude-adjusted signal into a digital value; A reference signal adjusting means for adjusting the magnitude of a reference signal in the transversal filter, and operations of the amplitude adjusting means and the reference signal adjusting means based on a calculation result of a tap gain near the main tap of the transversal filter. A waveform equalization circuit comprising a control means for controlling the waveform equalization circuit.