JPH06152723A - Radio telephone - Google Patents

Abstract

PURPOSE:To provide a radio telephone system which can maintain a stable speech, even if a volume operation is executed when a double talk state is detected. CONSTITUTION:In an echo canceller, an adaptive filter 47 generates an artificial echo signal, subtracts the artificial echo signal from a transmitting signal by a subtracter 48 and executes an adaptive operation in order to cancel an echo signal. When a double talk state is detected by a double talk detecting circuit 41, the adaptive filter 47 stops this adaptive operation. In order to execute matching of an A point input and a B point output, a digital volume 3 is provided on a transmitting output side of the double talk detecting circuit 41 in a transmitting path. Even if this digital volume 3 is operated in a double talk detecting state, a double talk detection level is not fluctuated, and a stop state of the adaptive operation can be maintained surely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiotelephone device having an echo canceller for canceling an acoustic echo generated during a hands-free call, which is used in a car telephone or the like.

[0002]

2. Description of the Related Art FIG. 4 shows a main structure of a call circuit in a conventional radiotelephone device of this type. A digital / analog (D / A) converter 6, a reception amplifier 7, a speaker 8 and a microphone. 12, transmission amplifier 11, analog volume 10, analog / digital (A / D) converter 9, PCM-CODEC 5, echo canceller 4, SP
It was composed of -CODEC2 and CH-CODEC1.

In this call circuit, the echo canceller 4 is used to prevent a part of the received voice output from the speaker 8 from entering the microphone 12 and being input, thereby impairing the call quality, and is usually an optional circuit. Is attached between PCM-CODEC5 and SP-CODEC2.

As can be seen from the figure, the echo canceller 4 includes an adaptive filter (ADF) 47 and a subtractor 4.
8, a double-talk detection circuit 41, and
The double talk detection circuit 41 includes absolute value detectors 42, 4
6, differential circuits 43 and 45, and a comparator 44.

In the receiving path of the communication circuit shown in FIG. 4,
Received signals from the other side input from the option terminal Rin are echo canceller 4, PCM-CODEC 5, D /
The received voice is reproduced from the speaker 8 through the A converter 6 and the reception amplifier 7.

Here, when a part of the reproduced received voice is input to the microphone 12 as an echo signal,
The input echo signal is a transmission amplifier 11, analog volume 10, A / D converter 9, PCM-CODEC 5
Through the option terminal Sin and echo canceller 4
To enter.

At this time, in the echo canceller 4, the adaptive filter 47 carries out an adaptive operation for canceling the echo signal which wraps around and enters the microphone 12. That is, in this adaptive operation, the adaptive filter 47 operates so as to make the residual signal from the subtractor 48 zero, thereby estimating the echo path to generate a pseudo echo signal from the received signal, and the pseudo echo signal. The signal is sent to the subtractor 48. Next, the subtractor 48 subtracts the pseudo echo signal from the echo signal input from the option terminal Sin.

The adaptive operation of the adaptive filter 47 acts to remove only the echo signal caused by the received voice reproduced from the speaker 8 when only the received signal is input from the option terminal Rin. , There is no problem in call quality.

However, in a so-called double-talk state in which the received signal is input from the option terminal Rin and the user's voice or the like (near-end talker signal) is also input from the microphone 12 at the same time, the adaptive operation is performed by the echo. Not only the signal but also the near-end talker signal will be removed together. Therefore, in this case, the transmitted voice signal is not transmitted to the other party even though the voice is transmitted, which seriously hinders the communication quality.

Therefore, in the echo canceller 4 of this type, in the double talk detection circuit 41, the double talk state is set as described above based on the received signal level input from the option terminal Rin and the transmission signal level input from the option terminal Sin. If it is detected whether or not there is a double-talk state, the fact is notified to the adaptive filter 47, and the adaptive operation is stopped. According to the control for stopping the adaptive operation of the adaptive filter 47 in the double talk state, it is possible to prevent the transmission signal from being unintentionally stopped in the double talk state and stabilize the call. .

By the way, in this type of radio telephone device, since the echo canceller 4 is optionally attached, in order to adjust the circuit condition when the echo canceller 4 is attached and when it is not attached. In addition, in the above communication circuit, it is necessary to match the A point input and the B point output (see FIG. 4).

In this type of conventional radiotelephone device, the analog volume 10 is used as a means for matching the above circuit conditions, and the arrangement stage is selected in the preceding stage of the echo canceller 4 in the transmission path. This configuration can be said to bring about a variation in the level of the transmission signal input from the option terminal Sin when the analog volume 10 is operated.

Therefore, if the double talk state is detected, the analog volume 10 is operated so as to reduce the volume of the transmission signal to a small level, and the option terminal Si
When the input level of the transmission signal for n becomes lower than the double-talk detection level, the double-talk detection circuit 41 of the echo canceller 4 changes the double-talk state to the non-detection state. In this case, since the adaptive filter 47 starts the adaptive operation, even the near-end talker signal is erased, and the transmission is completely interrupted.

[0014]

As described above, in the above-mentioned conventional radiotelephone device, in the speech circuit having the echo canceller which operates to stop the adaptive operation for canceling the echo signal when the double talk state is detected, the echo canceller is concerned. As a means for matching the signal level between the circuit units sandwiching the above, since the analog volume is arranged in the preceding stage of the echo canceller in the transmission path, when the analog volume is operated when the double talk state is detected, The transmission signal input level to the echo canceller changes, the double talk state changes to non-detection due to this, and the adaptive operation by the adaptive filter is restarted.
Even the near-end talker signal is erased, and there is a problem that the call quality is significantly impaired.

The present invention eliminates this problem, and when the double-talk state is detected in the echo canceller, even if the volume operation is performed, the double-talk state is not erroneously detected, and the stop control of the adaptive operation is performed. An object of the present invention is to provide a wireless telephone device that contributes to stable call holding in a double talk state while surely maintaining it.

[0016]

SUMMARY OF THE INVENTION A radiotelephone apparatus of the present invention subtracts a pseudo echo signal estimated from a received signal level from a transmission signal, and adaptively operates to cancel an echo signal so as to make the residual signal zero. And the echo signal canceling means for stopping the adaptive operation at the time when the double talk detecting means detects the double talk state in which the transmitting signal and the receiving signal exist at the same time, and intervenes in the transmitting path. The digital volume adjusting means is provided on the transmission output side of the double talk detecting means, and adjusts the signal level between the circuit parts sandwiching the echo signal erasing means.

[0017]

In the present invention, as a signal level matching means between the circuit parts sandwiching the echo canceller, a digital volume is arranged further on the transmission output side than the double talk detection circuit of the echo canceller in the transmission path. This configuration can be said to be a configuration in which the operation of the volume is not involved in the fluctuation of the transmission signal input level to the echo canceller. Therefore, even if the volume is operated in the double-talk state in which the reception signal and the transmission signal simultaneously occur, the double-talk detection level in the echo canceller does not have to fluctuate, and the adaptive operation of the adaptive filter is performed. It is possible to maintain a stable call in this double talk state while continuing the stop.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the wireless telephone device of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a wireless telephone device of the present invention,
Components having the same functions as those of the circuit units of the conventional device shown in FIG. 4 are designated by the same reference numerals. As can be seen from the figure, this wireless telephone device is different from the conventional device in that the echoes in the transmission path of the communication circuit are matched in order to match the signal levels of the A point input and the B point output. Canceller 4
The digital volume 3 is further provided on the transmission output side of the double talk detection circuit 41.

Next, the echo canceling processing operation of the device of the present invention will be described. In the reception path of the communication circuit shown in FIG. 1, the reception signal from the other side input from the option terminal Rin is an echo canceller 4 or PCM-CO.
It is reproduced as a received voice from the speaker 8 via the DEC 5, the D / A converter 6 and the receiving amplifier 7.

When a part of the reproduced received voice is input to the microphone 12 as an echo signal,
The input echo signal passes through the transmission amplifier 11, the A / D converter 9, and the PCM-CODEC 5, and is connected to the option terminal S.
Input from in to the echo canceller 4. At that time, in the echo canceller 4, the adaptive filter 47 performs an adaptive operation for canceling the echo signal input from the microphone 12. That is, in this adaptive operation, the adaptive filter 47 operates so as to make the residual signal from the subtractor 48 zero, thereby estimating the echo path to generate a pseudo echo signal from the received signal, and the pseudo echo signal. The signal is sent to the subtractor 48.

FIG. 2 is a detailed configuration diagram showing an embodiment of the adaptive filter 47, which includes a plurality of delay circuits (T) and
And a plurality of amplifiers having amplification factors (h0 to hM). In the adaptive operation described above, in the adaptive filter 47, the coefficients (h0 to hM) of each amplifier are changed according to the signal level of the transmission signal a taken after the echo cancellation processing and the reception signal x (n) at this time. By doing so, the pseudo echo signal y (n) is generated and output to the subtractor 48.

Next, the subtractor 48 subtracts the pseudo echo signal from the echo signal input from the option terminal Sin. As a result, it is possible to completely eliminate the echo signal that is the transmission signal at this time and is a cause of the deterioration of the speech quality. The adaptive operation in the adaptive filter 47 acts so as to remove only the echo signal caused by the received voice reproduced from the speaker 8 when only the received signal from the option terminal Rin is input. There is no problem in terms of quality.

However, in a so-called double-talk state in which the received signal is input from the option terminal Rin and the voice of the user (near-end talker signal) is also input from the microphone 12 at the same time, the adaptive operation is performed by the echo. Not only the signal but also the near-end talker signal will be removed together. Therefore, in this case, the transmitted voice signal is not transmitted to the other party even though the voice is transmitted, which seriously hinders the communication quality.

Therefore, in the echo canceller 4, in the double talk detection circuit 41, the option terminal Ri
Received signal level input from n and option terminal Sin
It is detected whether or not the double talk state is present on the basis of the transmission signal level inputted from, and when it is detected that the double talk state is given, the fact is notified to the adaptive filter 47 and the adaptive operation is stopped. I am trying to do it.

That is, in the double talk detection circuit 41, the absolute value detector 42 detects the absolute value of the received signal input from the option terminal Rin with respect to the reception path, and then the differentiating circuit 43 detects the peak of the absolute value of the received signal. The value is detected and the result is sent to the comparator 44. On the other hand, regarding the transmission path, the absolute value detector 46 detects the absolute value of the transmission signal input through the subtractor 48, and then the differentiating circuit 4
At 5, the peak value of the absolute value of the transmission signal is detected, and the result is sent to the comparator 44. As an example of this kind of circuit operation, FIG. 3 is a waveform diagram when an absolute value and a peak of an analog audio signal [see (a) in the figure] are detected [FIG. ) Reference] is shown.

Subsequently, the comparator 44 compares the respective peak values of the reception signal and the transmission signal, and outputs a detection signal indicating whether or not it is in the double talk state to the adaptive filter 47 according to the comparison result. . Here, when the adaptive filter 47 receives the detection signal indicating the double talk state from the comparator 44, the adaptive filter 47 operates so as to stop the above-described adaptive operation.

According to the control for stopping the adaptive operation of the adaptive filter 47 in the double talk state, it is possible to prevent the transmission signal from being unintentionally stopped in the double talk state and stabilize the communication. be able to.

In the wireless telephone device of the present invention, the echo canceller 4 is connected to the option terminals Rin, Rout, Si.
Matching between the A point input and the B point output when mounted as an optional circuit using n and Sout can be performed by appropriately operating the digital volume 3. In the present invention, this digital volume 3 is provided on the transmission output side of the double talk detection circuit 41 of the echo canceller 4 in the transmission path as described above.
According to such a configuration, it is obvious that the operation of the digital volume 3 does not participate in the level fluctuation of the transmission signal input from the option terminal Sin to the echo canceller 4.

Therefore, if the double talk detecting circuit 41 of the echo canceller 4 detects a double talk state and the digital volume 3 is operated to lower its volume, the option terminal Sin The input level of the transmission signal from is maintained at the same level as before. In this case, the double-talk detection circuit 41 is still in the state of detecting the double-talk state, and the adaptive filter (ADF) 47 is maintained in the state in which the adaptive operation is stopped. This allows
According to the present invention, even if the volume operation is performed in the double talk state, the transmission signal is not erased unnecessarily due to the fluctuation of the double talk detection level, and the stable call state can be maintained.

As disclosed in the present invention, in order to match the signal level between the circuits sandwiching the echo canceller 4, the digital volume 3 is provided on the transmission output side of the double talk detection circuit 41 in the transmission path. According to the configuration, it is possible to keep the input level of the codec or the like constant for each frame, particularly in a wireless telephone device that digitizes and transmits a voice signal.

[0031]

As described above, according to the present invention, since the digital volume is arranged on the transmission output side of the double talk detection circuit of the echo canceller in the transmission path, the double talk in which the reception signal and the transmission signal occur at the same time. In this state, even if the volume is operated, it is possible to detect the double talk accurately while suppressing the fluctuation of the double talk detection level. As a result, the adaptive operation in the adaptive filter is surely stopped and the double talk state is maintained. It has the great advantage of being able to maintain a natural call in.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a main part of a wireless telephone device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a detailed configuration of the adaptive filter shown in FIG.

FIG. 3 is a waveform diagram for explaining a double talk detection operation in the present invention.

FIG. 4 is a block diagram showing a circuit configuration of a main part of a conventional wireless telephone device.

[Explanation of symbols]

 1 CH-CODEC 2 SP-CODEC 3 Digital Volume 4 Echo Canceller 5 PCM-CODEC 6 Digital / Analog (D / A) Converter 7 Receiver Amplifier 8 Speaker 9 Analog / Digital (A / D) Converter 10 Analog Volume 11 Transmission Speech amplifier 12 Microphone 41 Double talk detection circuit 42,46 Absolute value detection circuit 43,45 Differentiation circuit 44 Comparator 47 Adaptive filter (ADF) 48 Subtractor

Claims (1)

[Claims] 1. A pseudo echo signal estimated from a received signal level is subtracted from a transmitted signal, an adaptive operation for canceling an echo signal is performed so that a residual signal thereof is zero, and a transmitted signal and a received signal are present at the same time. The echo signal canceling means for stopping the adaptive operation when the double talk detecting means detects that it is in the double talk state, and is provided on the transmission output side of the double talk detecting means interposed in the transmission path. And a digital volume adjusting means for matching the signal level between the circuit parts sandwiching the echo signal erasing means.