JPH0450773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit for canceling echoes in speech lines with large delays.

In telephone lines, there are both 2-wire and 4-wire lines, and a hybrid coil is used to convert between the two, but due to inconsistency in this hybrid coil, so-called echo occurs. . The present invention relates to a circuit for canceling such echoes.

(Prior Art and Problems) Fig. 2 shows an example of an echo canceller that has been used in the past, where 1 is a far-talker receiving input end, 2 is a far-talker receiving output end, and 3 is a near-talker transmitting input end. , 4 is a near talker side terminal, 5 is an adder that cancels the echo with a pseudo echo, 6 is an echo path model with a self-correction function, 7 is a hybrid coil, 8 is a near talker side terminal, 9 is a reception input It is a comparator that compares the signal and the transmitted input signal. The receiving side input signal X appearing at the far talker receiving input terminal 1 passes from the far talker receiving output terminal 2 to the hybrid coil 7 and appears as an actual echo signal Y at the near talker transmitting input terminal 3. This echo canceller cancels the actual echo by subtracting the pseudo echo signal Y^ generated by the echo path model 6 using the receiving side input signal X from the actual echo signal Y included in the transmitting input signal. The echo path model 6 has an echo path model 6 that corrects itself again using the residual component e that has been subtracted. When a simultaneous two-way conversation occurs, a signal completely different from the input signal
The echo path model 6 becomes unable to adapt to the actual echo path and ends up proceeding in the wrong direction. Therefore, in the conventional echo canceller, when the transmitting input signal Y becomes larger than the receiving side input signal X by a certain degree, the comparator 9 determines that it is a two-way simultaneous communication state and prohibits the correction function of the echo path model 6. There is. However, in reality, there is a time delay between the start of the simultaneous call and the detection, so the echo path model 6 deteriorates during that time.

A method to prevent this deterioration is to have two echo path models, one with a self-correction function and one without, and constantly compare the two, and replace the worse model with the better one. A method has also been proposed, and good characteristics can be obtained according to it, but in this case,
This method has the drawbacks of a complicated control method, an increased circuit scale, and a lack of practicality.

(Means for Solving the Problems) An object of the present invention is to provide an echo cancellation circuit that eliminates the problems of the conventional circuit described above and prevents deterioration of the echo path model during simultaneous two-way communication. be. In order to achieve this purpose, we provided a model state storage section that temporarily stores the model state of the echo path model circuit, and also provided a switch to transfer the model state between this model state storage section and the echo path model circuit. It is characterized by

(Example) Embodiments of the present invention shown in the drawings will be explained in detail below.

In FIG. 1, members that are the same or equivalent to those shown in FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted. In Figure 1, 10
is the state storage part of the model, 11 is the clock generator,
12 stores the state of the echo path model 6 in the state storage unit 1.
A switch 13 that shifts the state to 0 is a switch that shifts the state of the state storage section 10 to the echo path model 6. When there is no steady input signal from the near talker side terminal 8, the echo path model 6 is used as in the conventional example.
By generating a pseudo echo signal Y^ from the received input signal X, and subtracting it from the actual echo signal Y included in the transmitted input signal by the adder 5,
The echo is canceled and the echo path model 6 is modified using the residual echo signal e. Furthermore, in the embodiment of the present invention, the clock generator 11 generates pulses at a certain period T, and the periodic pulses periodically close the switch 12 and transfer the state of the echo path model 6 to the state storage section 10. This state storage section 10 can be configured using, for example, a memory element. The period T of the pulses generated by the clock generator 11, that is, the period of movement from the echo path model 6 to the state storage unit 10, is sufficiently large with respect to the detection delay time in the comparator 9 for detecting simultaneous two-way communication. Set it as follows.

Here, when an input signal from the near talker side terminal 8 is added and a simultaneous two-way conversation occurs, it is necessary to prohibit the correction operation of the echo path model as in the conventional example, so this must be detected. No. This operation is performed by the comparator 9. In this comparator, when the transmitted input signal Y becomes larger than the received input signal Prohibit modification functions. Furthermore, by moving from the echo path model 6 to the state storage section 10 in steady state, the state storage section 10 is not affected by deterioration due to detection delay, so it maintains a better model state than the echo path model 6. Since it can be considered, comparator 9
If a two-way simultaneous call is detected in
The switch 13 is closed and the state before the two-way simultaneous call is transferred from the state storage unit 10 to the echo path model 6, and the echo path model 6 uses that state.
A pseudo echo Y^ is generated. In addition, if it is determined that the comparator 9 has exited the state of simultaneous two-way communication in this state, the state returns to the initial state after a certain period of time to prevent false detection, and the echo path model is corrected. resume.

The above operation will be explained using FIG. 3. In this figure, the solid line shows the change in the amount of echo suppression according to the present invention, the dotted line shows the change in the amount of echo suppression according to the conventional example, and the dotted line shows the change in the amount of echo suppression according to the conventional example. In FIG. 3, when the present device is reset at time 0, the amount of echo suppression is increased by the above-mentioned correction operation, and after a certain period of time, the amount of echo suppression becomes constant. Here, since the clock generation period of the clock generator 11 is T, the echo path model 6
This means that the state has been transferred to the echo state storage section 10. Next, if a two-way simultaneous conversation state occurs at time t ₁ , the echo path model 6 begins to deteriorate and the amount of echo suppression decreases. Furthermore, when simultaneous two-way communication is detected at time _t2 , in the conventional example, the amount of echo suppression at this time is maintained. The time k periods after time 0 is T _k
Then, in the present invention, since the state of the echo path model stored at time T _i immediately before entering the two-way communication state is transferred to the echo path model 6, the amount of echo suppression can be returned to the amount of suppression at time T _i . , it is possible to maintain a high amount of echo suppression even during simultaneous two-way communication. Even if the two-way simultaneous conversation ends at time _t3 , in the conventional example, it takes time to return to the original echo suppression amount, whereas in the present invention, the echo suppression amount returns to the original echo suppression amount at time _{t2 .} Therefore, unlike conventional methods, there is no need for time to return to the original amount of suppression. Furthermore, even if the time at which the state of the echo path model 6 is transferred to the echo state storage section 10 is between the start time t ₁ and the detection time t ₂ of the simultaneous bidirectional path, the amount of deterioration can be reduced compared to the conventional method. . However, in the present invention, by lengthening the clock generation period T, that is, by lengthening the interval of movement from the echo path model 6 to the echo state storage unit 10, it is almost unnecessary to consider such a state. .

(Effects of the Invention) As explained above, by using the model state storage device, it is possible to prevent the echo path model from deteriorating during simultaneous two-way communication, and furthermore, it is possible to prevent the comparison operation of two models as in the conventional example. Since it does not contain any components, it has the advantage that good communication characteristics can be obtained with a simpler method and configuration.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention, FIG. 2 is a block circuit diagram showing a conventional example, and FIG. 3 is a diagram showing temporal changes in the amount of echo suppression. 1... Far talker reception input end, 2... Far talker reception output end, 3... Near talker transmission input end, 4... Near talker transmission output end, 5... Adder, 6... Echo Path model, 7... Hybrid coil, 8... Near talker side terminal, 9... Comparator, 10... State storage unit, 11
...Clock generator, 12...Switches 1, 13
...Switch 2.

Claims (1)

[Claims] 1 Generate a pseudo echo signal from the received input signal,
Eliminate the pseudo echo signal from the actual echo included in the transmitted input signal, and compare the transmitted input signal and the received input signal with an echo path model that corrects itself using the subtracted residual echo,
A model state of the echo path model in an echo cancellation circuit comprising: a comparator that detects a two-way simultaneous conversation state when a transmission input signal is larger than a reception input signal, and inhibits a correction function of the echo path model; a switch 1 for transferring the model state of the echo path model to the model state storage; a clock generator for opening and closing the switch 1 at a constant cycle; and a memory in the model state storage. a switch 2 for transferring the content to the echo path model; when the comparator detects a two-way simultaneous conversation state, closing the switch 2 inhibits the echo path model correction function and stores the model state. What is claimed is: 1. An echo cancellation circuit that prevents deterioration of an echo path model during a simultaneous two-way conversation by transferring an echo path model state immediately before a two-way simultaneous conversation state stored in the section to the echo path model.