JP3251177B2 - Echo reduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo reduction circuit suitable for use in a portable telephone having a hands-free communication function.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram showing a configuration of a portable telephone having a hands-free call function. In this figure, reference numerals 1 and 2 denote a transmitter (microphone) and a receiver (speaker) of the telephone body, respectively, and reference numerals 3 and 4 denote a transmitter (microphone) and a receiver (speaker) for hands-free communication. Reference numeral 5 denotes a hands-free communication circuit for preventing echo and howling caused by the sound output of the receiver 4 wrapping around the transmitter 3, and includes a comparator 6, a transmission attenuator 7, and a reception attenuator 8. The comparator 6 controls the transmission attenuator 7 and the reception attenuator 8 in a complementary manner in accordance with the transmission voice level and the reception voice level to keep a constant loop loss at all times.

In other words, the comparator 6 compares the transmission voice level with the reception voice level, and when the transmission voice level is higher than the reception voice level, increases the attenuation of the transmission attenuator 7 and reduces the attenuation of the reception attenuator 8. On the other hand, when the transmission voice level is lower than the reception voice level, control is performed so that the attenuation of the transmission attenuator 7 is reduced and the attenuation of the reception attenuator 8 is increased. Reference numerals 9 and 10 denote switches for switching the handsets 1 and 2 of the telephone set to the handsets 3 and 4 for hands-free calls in response to a switch signal output from the hands-free call switch detection circuit 11.

[0004] Reference numeral 12 denotes a transmitter which modulates transmission voice data obtained by sampling transmission voice input through the changeover switch 9 at a predetermined frequency, and then transmits and modulates the data. Reference numeral 13 denotes a duplexer, which wirelessly transmits the transmission output of the transmitter 12 from the antenna 15 and supplies a reception signal received via the antenna 15 to the receiver 14. The receiver 14 outputs the detected and demodulated received voice to the receiver 2 or the receiver 4 via the switch 10.

[0005]

When a hands-free call is made with the above-mentioned conventional portable telephone, the change-over switches 9 and 10 are respectively set to the telephones in accordance with the switching signal output from the hands-free call switch detection circuit 11. The handsets 1 and 2 on the main unit are replaced with handsets 3 and 4 for hands-free communication.
Switch to the side. When the hands-free call is selected in this way, the hands-free call circuit 5 prevents echoes and howling caused by the sound output of the receiver 4 wrapping around the transmitter 3. In use, the hands-free communication circuit 5 does not function, and the voice output of the receiver 2 goes around the transmitter 1 to generate an echo.

By the way, in a portable telephone, since the volume of the receiver is increased in consideration of use in a noisy environment, the volume easily reaches the transmitter 3. In recent years, digital type mobile phones have become widespread. However, since a mobile phone of this type has an audio delay, even a relatively small echo can be easily heard. As a method of actively canceling the echo, DS installed in the telephone
A method of echo cancellation by P is also conceivable.

However, in Japan, it is necessary to support the full rate and the half rate, and at the half rate, it is necessary to use the processing speed of the DSP to its limit. It is necessary to provide an IC and cancel the echo, resulting in a problem that the cost is increased.

The present invention has been made in view of such circumstances, and has as its object to provide an echo reduction circuit that can cancel echo with a simple configuration without increasing the cost.

[0009]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a signal CO for controlling a transmission attenuation and a reception attenuation in a complementary manner by comparing a transmission level with a reception level.
Comparison means for generating MP; transmission attenuation means interposed in the transmission line for generating transmission attenuation according to the signal COMP; and reception attenuation according to the signal COMP interposed in the reception line. When using a receiver attenuation unit that generates an amount and a handset for hands-free communication, the loop loss between the transmission attenuation unit and the reception attenuation unit is increased, and a handset on the main unit side is used. Comprises echo reduction means for reducing the echo by reducing the loop loss between the transmission attenuation means and the reception attenuation means, wherein the echo reduction means performs a hands-free call, in the case where the main body side call is performed, the signal COM that leads to the transmission attenuation means and said receiver attenuation means from said comparison means
Reduce the range of voltage level change in each of the P paths
A change in the voltage level of the signal COMP is switched by switching whether or not an amplifier is interposed , thereby changing the transmission attenuation generated by the transmission attenuation means and the reception attenuation generated by the reception attenuation means. Thus, the loop loss is variably controlled.

[0010]

[0011]

[0012]

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An echo reduction circuit according to the present invention
The present invention can be applied to a digital mobile phone having a hands-free function. Hereinafter, a mobile phone according to an embodiment of the present invention will be described as an example with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a portable telephone according to an embodiment of the present invention. Elements common to those of the conventional example shown in FIG. Shall be. The embodiment shown in FIG. 1 is different from the conventional example shown in FIG. 8 in that a transmission attenuator 21 and a comparator 2
2 and an echo attenuator 23 provided at the subsequent stage of the changeover switches 9 and 10.

The echo reduction circuit 20 is characterized in that attenuation characteristics are different between the case where the handsets 1 and 2 on the main body side are used and the case where handsets 3 and 4 for hands-free communication are used. That is, as shown in FIG. 2, the transmission attenuator 21 has an attenuation characteristic corresponding to the hands-free communication.
a, a main-unit transmission attenuator 21b having an attenuation characteristic corresponding to the main-unit-side transmitter 1, and a selection switch 21 for selecting one of these attenuators 21a, 21b
c, 21d.

The selection switches 21c and 21d are switched in response to a switching signal SEL output from the above-described hands-free call switching detection circuit 11. When the transmitter 1 on the main unit side is selected, the main unit call is switched. The transmission attenuator 21b is selected, and when the transmitter 3 for hands-free communication is selected, the transmission attenuator 21a for hands-free communication is selected.

Note that even in the receiving attenuator 23,
Although not shown, similarly to the transmission attenuator 21, a hands-free attenuator for hands-free communication having an attenuation characteristic corresponding to a hands-free communication (not shown, 23a is used for distinction from the attenuator 21a on the transmission side). Reference numeral) designates a main-unit-use receiving attenuator 23b having an attenuation characteristic corresponding to the main-unit-side receiver 2 (not shown, but 23b for distinction from the transmitting-side attenuator 21b).
And the attenuators 23a and 23b
(Not shown, but denoted by reference numerals 23c and 23d to distinguish them from the transmission-side selection switches 21c and 21d).

The transmission attenuator 21 and the reception attenuator 23 have the attenuation characteristics shown in FIG.
That is, the hands-free talk attenuator 21a on the talk attenuator 21 side has the attenuation characteristic ATT (1), and the main body talk attenuator 21b has the attenuation characteristic AT (1).
T (2). On the other hand, the transmitting attenuator 23a for hands-free communication on the receiving attenuator 23 side has an attenuation characteristic AT.
T (3), and the main-unit-use transmission attenuator 23b has the attenuation characteristic ATT (4).

In these attenuators 21a, 21b and 23a, 23b, the attenuation is controlled in a complementary manner in accordance with the output COMP of the comparator 22, which compares the transmitted voice level with the received voice level, and the loop loss is kept constant. ing. In the hands-free call, since the echo amount is large, a hands-free call transmission attenuator 21a having the attenuation characteristic ATT (1) and a hands-free call reception attenuator 23a having the attenuation characteristic ATT (3) are selected. Cancels echo with large loop loss.

On the other hand, in the main-unit call, the amount of echo from the receiver 2 to the transmitter 1 is small because the amount of acoustic coupling from the receiver 2 to the transmitter 1 is small. For this reason, the main unit transmission attenuator 21b having the attenuation characteristic ATT (2) and the main unit reception attenuator 23b having the attenuation characteristic ATT (4) are selected to cancel the echo.

By the way, the hands-free call switch detection circuit 11 for switching between the main-unit call and the hands-free call generates the switch signal SEL as follows. For example, FIG.
Is a hook detection mode. When the portable device main body 28 is stored in the in-vehicle adapter 29, the switch SW is closed to detect a hands-free call, and when the portable device main body 28 is not stored, the switch SW is opened and the main body call is performed. To detect. Also,
FIG. 5 shows a mode of switching to a hands-free call in response to an operation of the numeric keypad 30 on the portable device body. In this case, when a predetermined key is operated, the CPU 31 turns on the drive transistor 32, generates a switching signal SEL, and switches to a hands-free call.

As described above, in this embodiment, when the hands-free call switching detection circuit 11 switches to the hands-free call, the hands-free call transmission attenuator 21a having the attenuation characteristic ATT (1) and the attenuation characteristic ATT (3). The hands-free call attenuator 23a having the characteristic (1) is selected, thereby canceling the echo by increasing the loop loss. The telephone transmission attenuator 21b and the main telephone reception attenuator 23b having the attenuation characteristic ATT (4) are selected, thereby reducing the loop loss and eliminating the echo. Therefore, the echo is reduced with a simple configuration without increasing the cost. It is possible to cancel.

Next, a modified example of the present invention will be described with reference to FIGS. In the above-described embodiment, the transmission attenuator 21 is divided into a hands-free transmission attenuator 21a having an attenuation characteristic ATT (1) and a main body transmission attenuator 21b having an attenuation characteristic ATT (2), and the reception attenuator 23 is provided. ATT (3), hands-free call receiving attenuator 23a and attenuation characteristic ATT
(4) The system is configured so that it is divided into the main-unit call receiving attenuator 23b and is switched and selected according to the switching signal SEL, thereby giving a loop loss corresponding to each of the main-unit call and the hands-free call to cancel echo. However, in the modified example, a pair of transmitting and receiving attenuators 40 and 5 are used.
The attenuation amount of 0 is controlled in correspondence with the main unit call and the hands-free call. Hereinafter, this will be described.

First, the transmission attenuator 40 comprises components 40a to 40c. 40a is an amplifier for converting the voltage level V ₁ ~V ₃ output COMP of the comparator 6 to V ₁ ~V ₃ '. A switch 40b selects the output of the amplifier 40a or the input of the amplifier 40a in accordance with the switching signal SEL. That is, the input of the amplifier 40a is selected during a hands-free call, and the output of the amplifier 40a is selected during a main body-side call.

A reference numeral 40c designates an output COMP of the comparator 6 inputted through the switch 40b.
This is a transmission attenuator having an attenuation characteristic ATT (1) that changes as shown in FIG. That is, when the hands-free call, the attenuation amount changes according to the voltage level V ₁ ~V ₃ output COMP of the comparator 6. On the other hand, during a telephone conversation on the main unit side, the amount of attenuation changes in accordance with the voltage levels V _{1 to} V ₃ ′ converted by the amplifier 40a.

The receiving attenuator 50 includes a component 50
a to 50d. 50a is the output C of the comparator 6.
The voltage level V ₁ ~V ₃ of OMP is an amplifier for converting the V ₁ ~V ₃ '. 50b is a bias power supply for shifting the output level of the amplifier 50a. Reference numeral 50c denotes a switch for selecting the bias power supply 50b side during the main unit-side call and selecting the input of the amplifier 50a during the hands-free call.

Reference numeral 50d denotes an input through the switch 50c.
7 according to the output COMP of the comparator 6
It has the attenuation characteristic ATT (3) that changes as shown in (b).
One receiving attenuator. That is, hands-free communication
At the time of talking, the voltage level of the output COMP of the comparator 6 is
Le V₁~ V_ThreeThe amount of attenuation changes according to. On the other hand,
When talking, the range is converted by the amplifier 40a.
And bias-shifted voltage level V ₁’-V_Three
The amount of attenuation changes according to.

According to the modification of the above-described configuration, in the hands-free communication, the attenuation of both the transmission / reception attenuators 40 and 50 changes according to the voltage levels V _{1 to} V ₃ , so that the loop loss is increased and the echo is reduced. to erase. On the other hand, in the case of the main unit side call, the attenuation of the output COMP of the comparator 6 in the transmission attenuator 40 changes within the range of voltages V _{1 to} V ₃ ′, and the output C of the comparator 6 in the reception attenuator 50.
Since the amount of attenuation changes in the range of the OMP voltage V ₁ ′ to V ₃ ,
The echo is canceled by reducing the loop loss. As described above, in the modified example, the echo in the case of the main-unit-side call and the hands-free call can be canceled only by the pair of transmitting / receiving attenuators 40 and 50, so that the configuration is further simplified and the product price is reduced. It is possible to contribute.

[0029]

According to the present invention, the change in the voltage level in the path from the signal COMP to the transmitting side and the receiving side attenuator is achieved.
By switching the variation range of the voltage level of the signal COMP the amplifier for the reduction range as small switches whether to or not to intervention, when using handset for handsfree call, and the transmission attenuation means When the loop loss with the reception attenuation means is increased, and the handset on the main body side is used, the echo can be reduced by reducing the loop loss between the transmission attenuation means and the reception attenuation means, Echo cancellation can be performed with a simple configuration.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a configuration of a transmission attenuator 21.

3 is a diagram illustrating attenuation characteristics of a transmission attenuator 21 and a reception attenuator 23. FIG.

FIG. 4 is a diagram for explaining one mode of hands-free call switching detection.

FIG. 5 is a diagram for explaining one mode of hands-free call switching detection.

FIG. 6 is a block diagram showing a configuration of a modification.

FIG. 7 is a diagram for explaining an operation of a modified example.

FIG. 8 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

1, handset-side handset 3,4 Hands-free phone handset 9,10 selector switch 11 hands-free phone call switching detection circuit 21 speech attenuator (ATT) (speech attenuating means, first echo reduction means) 22 comparator (Comparing Means) 23 Receive Attenuator (ATT) (Receiver Attenuating Means, Second Echo Reduction Means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04M 1/60 H04B 3/20

Claims (1)

(57) [Claims] 1. A signal CO that compares a transmission level and a reception level to control transmission attenuation and reception attenuation in a complementary manner.
Comparison means for generating MP; transmission attenuation means interposed in a transmission line for generating transmission attenuation according to the signal COMP; reception attenuation in accordance with the signal COMP interposed in a reception line When using a receiver attenuating means for generating an amount and a handset for hands-free communication, the loop loss between the transmission attenuating means and the receiver attenuating means is increased, and a handset on the main body side is used. Comprises echo reduction means for reducing the echo by reducing the loop loss between the transmission attenuation means and the reception attenuation means, wherein the echo reduction means performs a hands-free call; When the main unit side call is made,
The variation range of the voltage level to each of the signal <br/> No. COMP path leading to the transmitter attenuating means and said receiver attenuation means
The switching range of the voltage level of the signal COMP is switched by switching whether or not to use an amplifier to be reduced.
Switch the circumference, echo reduction circuit, characterized by variably controlling the loop loss transmission loss and the receiver attenuating means alters the reception attenuation amount generated to the transmission attenuation means is generated.