JPH0260269A - Hand-free calling circuit - Google Patents

Abstract

PURPOSE:To prevent an ambient noise from being interrupted thoroughly, and to realize smooth calling at the time of a turn from a talking state to a receiving state by changing a variable insertion loss and an ambient noise signal level complementarily. CONSTITUTION:In the case of turning from the talking state to a non-calling state, and in the case of turning from the non-calling state to the receiving state, a comparison control circuit 62 changes control signals C to F. Thus, the attenuation quantity of an electronic volume 20a is changed from the minimum (0db) to the maximum (-20dB), and the attenuation quantities of the electronic volumes 30a and 42a are changed from the maximum (-20dB) to the minimum (0dB), and an analog switch 43a is turned from OFF to ON. The change to the time of the attenuation quantity of the electronic volume 42a is made same as the electronic volume 30a of a receiving channel, and its attenuation is made smaller gradually when the attenuation of the signal level of transmission channel is made larger gradually on the decision of the receiving state or the non-calling state.

Description

[Detailed Description of the Invention] (Required II) To enable a smooth call without giving the other party the feeling that the line is disconnected, regarding a hands-free call circuit used in car phones, etc. In addition, the purpose is to enable two-way communication in a double talk state, and in a hands-free communication circuit that has variable insertion loss in each of the sending and receiving paths, it has a predetermined characteristic based on the signal from the microphone. ambient noise generation means for generating an ambient noise signal; addition means for adding the ambient noise signal generated by the ambient noise generation means and the output of the variable insertion loss on the sending path side; and signal levels for the sending path and the receiving path. According to this, an ambient noise generating means and a IIIwJ means for adjusting the variable insertion loss provided in the transmitting path and the receiving path are provided.

[Industrial application field]

TECHNICAL FIELD The present invention relates to a hands-free communication circuit used in automobile telephones and the like.

Hands-free communication circuits are used in so-called public address telephones. This public address telephone is a telephone that uses a microphone and a speaker instead of a handset. The hands-free call circuit has a microphone amplifier, a speaker amplifier, a howling prevention function, a voice switch function, etc.

[Conventional technology]

FIG. 10 shows a block diagram of a conventionally used hands-free communication circuit. The hands-free communication circuit shown in the figure compares the levels of sending and receiving audio signals detected by audio detection circuits 2 and 4, which are composed of AC-DC conversion circuits, etc., in a comparison/control circuit 5, and compares the levels with a variable insertion loss 1. and control the transmission loss of 3. In this case, a large insertion loss is given to the communication path where the signal level is low to prevent howling, echoes, etc. In addition, in the figure, 6 is a microphone, 7 is a speaker, 8 is a wireless transmission/reception circuit, 9 is a microphone amplifier, and 1
0 is a speaker amplifier.

[Problem to be solved by the invention]

However, the above-mentioned conventional hands-free communication circuit has the following problems.

During reception in a normal single talk state, as described above, the insertion loss of the variable insertion loss 1 provided on the microphone 1 side is set to a large value to block ambient noise entering from the microphone. For this reason, there is a problem in that the person on the other end of the line feels as if the line has been disconnected, which hinders smooth communication.

In particular, in hands-free communication using automatic 111 talk, ambient noise such as driving noise is large, so the above problem becomes serious.

Furthermore, since an insertion loss of 1 or 3 is applied to one communication path, there is also the problem that communication in a double talk state is hindered.

Therefore, the present invention solves the above-mentioned problems, enables smooth communication without giving the other party the feeling that the line has been disconnected, and enables two-way communication in a double talk state. The purpose is to

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the present invention.

The ambient noise generating means 40 generates an ambient noise signal having predetermined characteristics based on the signal from the microphone.

The adding means 50 adds the ambient noise signal generated by the surrounding i name generating means 40 and the output of the variable insertion loss 20 on the channel side.

The control means 60 controls the ambient noise generation means 40 and the variable insertion loss 20.30 provided in the sending and receiving paths according to the signal levels of the sending and receiving paths.

[Effect]

1131111 The means 60 increases the attenuation amount of the variable insertion loss 20 on the sending path side and reduces the variable insertion loss 3 on the receiving path side when it is determined that the receiving state is based on the signal levels of the sending path and the receiving path.
0 and the ambient noise signal generated by the ambient noise generating means 40. in this case,
Since there is no longer any voice from the speaker, the output of the adding means 50 becomes an ambient noise signal of increasing signal level. In this way, the control means 60 changes the variable insertion loss 20 and the ambient noise signal level in a complementary manner, so that when changing from the transmitting state to the receiving state, smooth communication can be achieved without completely blocking out the ambient noise. becomes possible. Further, since the attenuation of the variable insertion loss 20 does not increase rapidly but increases over time, it is possible to perform two-way communication in a double talk state.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention. In the figure, the ambient noise generating means 40 of FIG.
Wave device 41. Variable loss circuit 42 and 0N10FF circuit 43
It is equipped with: The low frequency wave generator 41 inputs the signal from the micro. Preferably, as shown in FIG. 3, a micro is used that has a characteristic that the high frequency level increases by, for example, +6 dB/octave. This improves clarity. The low-frequency P wave device 41 passes only the low-frequency signal component of the signal from the micro (attenuates the high-frequency signal component), and has frequency characteristics opposite to those of the micro, as shown in FIG. 4, for example. use something As a result, the output of the low-pass p-wave converter 41 becomes approximately flat as shown in FIG. This output signal is used as an ambient noise component and is applied to the variable loss circuit 42. Variable loss circuit 42
The attenuation amount of the variable loss is set so that the attenuation amount of the ambient noise component is changed complementary to the change in the attenuation amount of the variable insertion loss 20. This control is performed by the comparison/control circuit 62 of the control means 60. The 0N10FF circuit 43 is used when transmitting a call.
The output of the variable loss circuit 42 is blocked, and the output is allowed to pass at other times (when there is no call, reception, or double talk).

The control means 60 includes volume detection circuits 61 and 63 . It also has a comparison/control circuit 62. Volume detection circuits 61 and 63 detect the signal levels of the sending path and receiving path, respectively. The comparison/control circuit 62, depending on the detected signal level,
Variable insertion loss 20 and 30. Variable loss circuit 42. Also, the 0N10FF circuit 43 is controlled as described later.

FIG. 6 shows a more specific version of the block configuration shown in FIG. For example, the low-frequency P wave generator 41 shown in FIG. 2 has a cutoff frequency fc = 300Hz and a gain G = -6.
Order low pass filter (LPF>).

It is 41a. The variable loss circuit 42 is an electronic volume 42
Consists of a. Similarly, the variable insertion losses 20 and 30 are also composed of electronic volumes 20a and 30a. 0N1
The 0FF circuit 43 is composed of an analog switch 43a. The addition means 50 is composed of an addition amplifier 50a.

Next, the operation of this embodiment will be explained with reference to the operation timing chart of FIG.

First, in the transmitting state, the output A of the volume detection circuit 61 is at a high level (FIG. 7(a)), and the output B of the volume detection circuit 63 is at a low level (FIG. 7(b)).

The comparison/control circuit 62 detects this and adds the summing amplifier 50a.
, the Ti child volume 20a, the electronic volume 42a, and the electronic volume 30a in FIGS. 7(c) to 7(f), respectively.
) outputs control signals C, D, E and F shown in FIG. As a result, the amount of attenuation of the electronic volume 20a is minimum (O output),
The attenuation amount of electronic volumes 30a and 42a is maximum (-20
dB), the analog switch 43a is turned OFF.

In this state, the audio signal from the micro is transmitted to the microphone amplifier 9.
° The signal passes through the electronic volume 20a and the analog switch 43a as is, and is transmitted via the wireless transmitting/receiving circuit 8.

Next, the operations when changing from the transmitting state to the no-calling state and when changing from the no-calling state to the receiving state will be explained. In these states, as shown in FIG. 7, only the levels of the outputs A and B of the voice detection circuits 61 and 63 are different, and the control signals C to F output by the comparison/control circuit 62 are the same. In these states, the comparison/control circuit 6
2 changes the control signal C-F as shown in FIGS. 7(C) to (f). As a result, the attenuation amount of the electronic volume 20a changes from the minimum (OdB) to the maximum (-20 dB), and the attenuation amount of the electronic volumes 30a and 428 changes to the maximum (-20 dB).
0cf5) to the minimum (Od3), and the analog switch 438 changes from OFF to ON. In this state, the signal from the micro goes through the microphone amplifier 9, the first-order low-pass filter 41a, the '1 child volume 42a, and the analog switch 43a, and is applied to the summing amplifier 50a. As described above, the output of the first-order low-pass filter 41a has a substantially flat frequency characteristic as shown in FIG. 5, and this is used as an ambient noise component. In addition, the change in the amount of attenuation with respect to time of the electronic volume 42a is made the same as that of the electronic volume 30a on the receiving path side, and when the attenuation of the signal level of the transmission path is increased when it is determined that the receiving state or the non-talking state is reached, the attenuation amount is Make it smaller.

FIG. 8 is a diagram showing how the amount of attenuation changes over time. The solid lines in the figure relate to the electronic volume 20a, and the broken lines relate to the electronic volumes 308 and 42a. In the receiving state or in the non-calling state, there is no voice from the caller, so that the signal passing through the first-order low-pass filter 41a is mostly composed of ambient noise components. Add this to 50 amplifiers
At step a, it is added to the transmitted voice signal output from the electronic volume 20a. The amount of attenuation of the electronic volume 20a and the amount of attenuation of the electronic volume 42a change complementary to each other as shown in FIG. The transition between ambient noise and ambient noise is smooth.

Next, during double talk, the outputs A and B of the voice detection circuits 61 and 63 are as shown in FIGS. 7(a) and (b).
Both are of a high level. Even in this state, the comparison/control circuit 62 outputs the same control signals C to F as in the above-mentioned no-call state and call-receiving state. Therefore, the signal from the micro is outputted from the first-order low-pass filter 41a through the electronic volume 42a, the analog switch 438, and the summing amplifier 50a in the same manner as described above. Therefore, two-way communication becomes possible to some extent (although the quality of the communication deteriorates).

Here, the insertion loss in the transmission path is the electronic volume 20
a, the first-order low-pass filter 41a, and the electronic volume 42
It is the sum of the attenuation amount of a. In a complete listening state, the amount of attenuation of the electronic volume 42a is minimum, and the amount of attenuation of the electronic volume 20a is maximum. In this state, there is an insertion loss corresponding to the amount of attenuation of the first-order low-pass filter 41a, so a howling margin can be secured accordingly. In particular, since low-frequency noise is low in a car phone, the margin shown in the figure is useful. This is shown in the shaded area in FIG. Since such a howling margin can be ensured, reception can be performed without blocking ambient noise even in a receiving single talk state. If a similar circuit is provided on the receiver side, the same effect can be obtained even in the transmitting single talk state.

One embodiment of the present invention has been described above. In the above example,
Although the low-pass filter 41 is configured with a first-order low-pass filter 41a, a second-order or higher-order low-pass filter can be used. FIG. 9 is a frequency characteristic diagram of a second-order low-pass filter. The shaded area in FIG. 9 is the howling margin. Furthermore, an equalizer with arbitrary frequency characteristics may be used. In this case as well, a howling margin can be provided depending on the characteristics.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to have a smooth conversation without giving the other party the feeling that the line has been disconnected, and also to realize two-way conversation in a double talk state. can get.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the principle of the present invention, Figure 2 is a block diagram of an embodiment of the present invention, Figure 3 is a frequency characteristic diagram of the microphone used in this embodiment, and Figure 4 is a diagram of the frequency characteristics of the microphone used in this embodiment. Figure 5 is a frequency characteristic diagram from the microphone input to the low-pass filter in this embodiment; Figure 6 is a specific configuration diagram of this embodiment; The figure is an operation timing diagram of this embodiment, FIG. 8 is a diagram showing changes in attenuation amount with respect to time, and FIG. 9 is a frequency characteristic diagram of a second-order low-pass filter that can be used in this embodiment.
and FIG. 10 are block diagrams of a conventional hands-free communication circuit. In the figure, 20 is a variable insertion loss, 30 is a variable insertion loss, 40 is an ambient noise generation means, 41 is a low TaP wave generator, 42 is a variable loss circuit, 43 is a 0N10FF circuit, 50 is an addition means, 60 is a control means, 61 is a volume detection circuit, 62 is a comparison/control circuit, and 63 is a volume detection circuit.

Claims (1)

[Claims] Variable insertion loss (20, 30
), the hands-free communication circuit includes: an ambient noise generating means (40) that generates an ambient noise signal having predetermined characteristics based on a signal from a microphone; and an ambient noise signal generated by the ambient noise generating means (40). an addition means (50) for adding the output of the variable insertion loss (20) on the sending path side; A hands-free communication circuit, comprising: control means (60) for controlling variable insertion loss (20, 30) provided in the hands-free communication circuit.