JP3314372B2 - Full-duplex audio communication circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full-duplex audio communication circuit used for a handset unit of a communication device, a radio transceiver, a portable telephone, and the like. In particular, the present invention relates to a full-duplex communication circuit using only one transducer having a function of converting sound into an electric transmission signal and simultaneously converting an electric reception signal into sound. More specifically, the present invention relates to a full-duplex communication circuit using one transducer without using a transmitter and a receiver separately.

[0002]

2. Description of the Related Art Full-duplex communication has advantages over half-duplex communication because both parties can simultaneously make and receive calls.

However, full-duplex communication is a closed loop circuit for transmitting and receiving simultaneously. The total loop gain must be less than 1 so that there is no feedback there. Such devices usually had separate speakers and microphones.

[0004] US Patent No. 4,002,860 provides a method for solving the audio feedback problem.
The communication device described in the patent is a transducer that serves as a speaker and a microphone for canceling audio feedback.
(Transducer) is used. However, the circuit design described in the patent failed to effectively cancel the electrical feedback.

In order to further improve the electric signal feedback, a full-duplex audio communication circuit 100 of a communication device 200 using the transducers 101 and 102 has been proposed as shown in FIG. Here,
The communication device main body 200 is a portable telephone main body, and
The transducers 101 and 102 will be described as earphones having a microphone function.

The principle is described below. First, a carrier signal from an antenna or the like is demodulated into an audio signal by a receiving unit of the communication device main body 200, and the received signal R is input to the operational amplifier circuit 103, amplified, and then input to the operational amplifier circuits 104 and 105, respectively. . These amplified outputs enter the differential amplifier circuit of the operational amplifier circuit 106.

The input signal of the operational amplifier circuit 106 has an amplitude
Since the phase is the same, the output signal is canceled, and at the same time, the received signal becomes an acoustic output from the transducers 101 and 102, and the sound enters each ear.

That is, this circuit is a cancel circuit for canceling a received signal so as not to enter a transmission signal component.

On the other hand, the sound to be transmitted is obtained by converting the vibration in each ear (air vibration of the inner ear) into the transducer 10.
1, 102 detects and converts it into an audio signal. These audio signals are respectively supplied to an operational amplifier circuit 10
4, 105 and amplified. Here, since the polarities of the transducers 101 and 102 are previously set to the opposite polarities, the operational amplifier circuit 106 becomes the sum of those audio signals. The audio signal of this sum enters the transmission section of the communication apparatus main body 200 as a transmission output S, where it is FM-modulated and becomes a carrier signal, which is radiated from the antenna.

As described above, the transducer 10
By using 1,102, in the transmission signal S,
By the cancellation circuit in which the component of the reception signal R is canceled,
The cancellation amount of the electric signal feedback was set to −40 db or less.

[0011]

However, the method for improving the electrical feedback as shown in FIG. 6 has the following problems .

The first disadvantage is that two earphones as transducers are required. That is, the transducer must be placed in both ears.
The need for two was very cumbersome.

A second disadvantage is that the cancellation circuit of FIG. 6 reduces the amount of cancellation of the electric signal feedback by -4.
In order to reduce the value to 0 db or less, it is necessary to accurately set each circuit constant of the cancel circuit. In particular, it is difficult to keep the characteristics of both earphones exactly the same, and if each circuit constant has a shift or movement of a constant that is a little smaller than the set value, the disadvantage is that the amount of cancellation rapidly decreases. is there.

Therefore, it is not a stable cancellation circuit for actual use.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned point, and an object thereof is to provide only one earphone having a function of a transducer, that is, a microphone, and to provide a cancel circuit which operates stably. It is to provide a heavy audio communication circuit.

[0016]

In order to solve the above-mentioned problems, a full-duplex audio communication circuit according to the present invention is a full-duplex audio communication circuit used for a handset of a communication device, wherein an audio input is electrically connected. A transducer (Trans
ducer), a differential amplifier circuit for outputting a transmission signal to a transmission amplifier circuit, and a reception signal from the reception amplifier circuit for branching and connecting to a first input terminal and a second input terminal of the differential amplifier circuit, respectively. A first output circuit of the branch circuit is connected to the first input terminal while a first output circuit of the branch circuit is connected to the first input terminal, and the transducer is formed of a resistance circuit. And a resistor connected to the second input terminal via a resistor, whereby the signal from the receiving amplifier circuit has the same amplitude at the first input terminal and the second input terminal of the differential amplifier circuit by the resistor circuit. It is characterized by the following.

A full-duplex audio communication circuit for use in a handset of a communication device, comprising: a transducer for converting an audio input signal into an electric transmission signal while converting an electric reception signal into an audio output signal; A differential amplifier circuit for outputting to the transmission amplifier circuit, and a branch circuit for branching a reception signal from the reception amplifier circuit and connecting to a first input terminal and a second input terminal of the differential amplifier circuit, respectively. The first output circuit of the branch circuit is formed of an impedance circuit and is grounded via a resistor, is connected to the first input terminal, and the second output circuit is formed of a resistance circuit and is grounded via the transducer. Connected to the second input terminal via a resistor, and a signal from the receiving amplifier circuit is supplied to the first input terminal of the differential amplifier circuit by the impedance circuit and the resistor circuit. As each amplitude same at the second input terminal, characterized in that the phase-phase.

Further, the impedance circuit according to the present invention is characterized by comprising a series circuit of a resistor and a capacitor.

Further, the communication device according to claim 1, 2, or 3 is a portable telephone.

Further, the transducer according to the first, second, third or fourth aspect is a magnetic earphone, a dynamic earphone or a crystal earphone having a microphone function.

A full-duplex audio communication circuit for use in a handset of a communication device, comprising: a transducer for converting a sound input into an electric transmission signal and, at the same time, converting an electric reception signal into a sound output; A differential amplifier circuit for outputting to the transmission amplifier circuit, and a branch circuit for branching a reception signal from the reception amplifier circuit and connecting to a first input terminal and a second input terminal of the differential amplifier circuit, respectively. The first output circuit of the branch circuit is formed of a resistor circuit and grounded via an impedance circuit, and is connected to the first input terminal, and the second output circuit is formed of a resistor circuit and grounded via the transducer. Connected to the second input terminal via a resistor, and a signal from the receiving amplifier circuit is connected to the first input terminal of the differential amplifier circuit by the impedance circuit. Each amplitude same at the second input terminal, characterized in that the phase-phase.

Further, the impedance circuit according to claim 6 comprises a series circuit of a resistor and a capacitor when the transducer is a crystal earphone, and comprises a series circuit of a resistor and a coil when the transducer is a magnetic earphone or a dynamic earphone. It is characterized by becoming.

A full-duplex audio communication circuit, wherein the communication device according to claim 6 or 7 is a portable telephone.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. In the full-duplex audio communication circuit 1 of FIG. 1, 200 is a communication device main body, 200a is an input terminal of an audio transmission signal S of the other party, and 200b is an output terminal of an audio reception signal R from the other party. Reference numerals 2 and 3 denote operational amplifier circuits for amplifying the received signal R, 11 denotes a branch circuit, 11a denotes a first output circuit, 11b denotes a second output circuit, and both are resistance circuits in the first embodiment. 10 is a transducer, an earphone having a microphone function, 9 is a differential amplifier circuit, 9a is a first input terminal, 9
b is a second input terminal. Here, the first output circuit 1
Reference numeral 1a is connected to a first input terminal 9a, and the second output circuit 11b is connected to an earphone 10 having the function of the microphone, and is also connected to a second input terminal 9b via a resistor. Reference numeral 7 denotes an operational amplifier for amplifying the output of the differential amplifier circuit 9, and reference numeral 8 denotes a stabilized DC current circuit.

The operation of the full-duplex audio communication circuit 1 is as follows. The received signal R, which is an audio signal demodulated by the receiving unit of the communication device main body 200, is output from its output terminal 20.
0b, passes through a filter circuit for attenuating high frequency components and the like, and is amplified by operational amplifier amplifier circuits 5 and 6,
Input to the branch circuit 11. Here, the received signal R is input to the earphone 10 having a microphone function via the second output circuit 11b, and a sound is output. At the same time, the signal is input to the second input terminal 9b of the differential amplifier circuit 9 via the resistor via the second output circuit 11b. On the other hand, the reception signal R of the first output circuit 11 a of the branch circuit 11 is input to the first input terminal 9 a of the differential amplifier circuit 9.

The difference between the received signals of the first input terminal 9a and the second input terminal 9b is output from the output terminal of the differential amplifier circuit 9, and the amplitude of the input of the received signals is made equal. If the resistance values of the first output circuit and the second output circuit are determined as described above, the reception signal R becomes 0 at the output terminal of the differential amplifier circuit 9. Thus, there is little electrical feedback.

On the other hand, the sound is detected by the earphone 10 having a microphone function due to the air vibration in the inner ear and becomes an electric audio signal, that is, a transmission signal S, which is input to the second input terminal 9b of the differential amplifier circuit 9, It is amplified and becomes the transmission output S.

Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment of FIG. 2 is a further improvement of the first embodiment of FIG.

As can be seen from the equivalent circuit of the transducer 10 as shown in FIG. This is an impedance including an inductance component of the coil L.

For example, in the case of an earphone having a certain microphone function, r = 95Ω and L = 80 mH.

When there is such an inductance component, the received signal at the second input terminal 9b of the differential amplifier circuit 9 is generated by the inductance component of the transducer 10 which is in parallel with the second output circuit 11b or 12b of the branch circuit 11. The phase of R leads the received signal R at the first input terminal 9a. Therefore, even if only the amplitude component of the received signal R is the same as in the first embodiment of FIG. 1, the output of the differential amplifier circuit 9 is not zero due to the phase difference of the received signal.
This causes electrical feedback.

FIG. 2 of the second embodiment of the present invention can cope with a case where the inductance component of the transducer 10 cannot be ignored.

Here, the reference numerals in FIG. 2 will be described. The same reference numerals as those in FIG. 1 have the same functions, and the description will be omitted.
In FIG. 2, reference numeral 12 denotes a branch circuit of the second embodiment,
2a is an impedance circuit as its first output circuit, 1
2b is a resistor circuit as the second output circuit.

The impedance circuit 12a is a circuit for adjusting the phase shift of the received signal due to the inductance component. Since the received signal at the second input terminal 9b of the differential amplifier circuit 9 has a phase advanced from the received signal at the first input terminal 9a due to the inductance component of the transducer 10,
The impedance circuit 12a may advance the phase of the received signal at the first input terminal 9a by that amount. FIG. 3 (b)
Shows an example of the circuit. This is a series circuit of a resistor R and a capacitor C. With such a series circuit, the amplitude and phase of the received signal at the first input terminal 9a and the amplitude of the received signal at the second input terminal 9b of the differential amplifier circuit 9 can be made the same. Therefore, by the impedance circuit 12a of the second embodiment,
Even when the inductance component of the transducer 10 cannot be ignored, this effect can be canceled and the received signal R on the output side of the differential amplifier circuit 9 can be completely set to 0, so that the electrical feedback can be suppressed stably. be able to.

A function for canceling the influence of the inductance component.
Will be described in more detail. Now, in FIGS. 2 and 3,
Voltage at output point of operational amplifier 6 (branch point of branch circuit 12)
To e_R, The second output circuit (resistance circuit) 12b and the transformer
The voltage at the connection point of the_M, The first output circuit (in
The voltage at the connection point between the impedance circuit 12a and the resistor R9 is
e_AAnd The resistance of the second output circuit 12b is R0.
The resistor R0 is connected to the input of the differential amplifier circuit 9 via the resistor R1.
Assume that it is connected to terminal 9b. However, R1 >> R0 and
I do. Here, angular frequency ω = 2πf (f: frequency) and
Then, if j = √ (−1), e _MAnd e_RIs the voltage ratio K1
It becomes like the following formula. K1 = (e_M/ E_R) = (R + jωL) / {(r + R0) + jωL} (1) Here, when ω is large, K1 → 1. ω is small
In this case, K1 = r / (r + R0), and a value close to 0 is obtained.
Become. That is, e_MIs, as can be seen from equation (1),
It is almost proportional to the wave number ω. On the other hand, e_AIs e_MAmplitude and phase
Do not match, the output of the differential amplifier circuit 9 is e_RMinute
Is not output, so e_AMust also be proportional to ω
I have to. Therefore, the impedance circuit 12a
A capacitance C must be connected in series. Sand
Chi, e_RAnd e_RIs expressed by the following equation. K2 = (e_A/ E_R) = R9 / {(R9 + R) + (1 / jωC)} (2) Here, if ω is large, K2 = R9 / (R9 + R).
If R9 >> R, K2 → 1. When ω is small, K
2 → 0. Therefore, both are proportional to the angular frequency ω
Therefore, if a constant is selected, the frequency
Both input terminals 9a and 9b of the amplifier 9 have an angular frequency ω
The same amplitude. Therefore, e_RHa
Canceled. FIG. 4 shows a full-duplex audio according to another embodiment.
1 shows a communication circuit 3. Full-duplex audio of the embodiment of FIG.
A resistor r 'and a coil L' instead of R9 in the radio communication circuit 2
Provide impedance circuit 13 consisting of
Trying to do it. Now, R1 >> R0, R0 = R
Then, if L ′ = L and r ′ = r, then (r + jω
L) / {(r + R0) + jωL} (r ′ + jωL ′)
/ {(R ′ + R) + jωL ′}, and e_M≒ e_ATona
And is canceled with the same phase and the same amplitude.
The output is e_RThe ingredients are gone. FIG. 5 shows still another implementation.
1 shows an example full-duplex audio communication circuit 4; This example shows a tiger
The transducer 20 is a crystal earphone (piezo
Hong). Capacitive as also shown in FIG.
It is a circuit which becomes. Where C_MAnd r_MSeries circuit
This is an equivalent circuit of a Lister earphone. Cancel this
To do this, as shown in FIG.
C '_MAnd r ' _MIs required. In the case of FIG.
Similarly, assuming that R1 >> R0 and R0 = R, C ′_M=
C_M, R '_M= R, then e_M≒ e_ANext
The phase is canceled at the same phase and the same amplitude.
E for power_RThe ingredients are gone.

[0036]

The full-duplex audio communication circuit of the present invention has the following effects. (1) Conventionally, two transducers such as earphones having the function of a microphone were required, which was troublesome for the ear. However, the present invention requires only one transducer, and the effect that the trouble for the ear is greatly reduced compared to the conventional art. There is. (2) Even when the inductance component or the capacitance component of an earphone or the like having a microphone function cannot be neglected, this effect is canceled and the effect of performing stable full-duplex audio communication without completely electrical feedback is obtained. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of a full-duplex audio communication circuit according to the present invention.

FIG. 2 is a block diagram of a second embodiment of a full-duplex audio communication circuit according to the present invention.

3A is an equivalent circuit diagram of an earphone having a microphone function, and FIG. 3B is a circuit diagram of one embodiment of an impedance circuit.

FIG. 4 is a block diagram of a third embodiment of the full-duplex audio communication circuit of the present invention.

FIG. 5 is a block diagram of a fourth embodiment of a full-duplex audio communication circuit according to the present invention.

FIG. 6 is a block diagram of a conventional full-duplex audio communication circuit.

[Explanation of symbols]

R audio reception signal S audio transmission signal 1,2,3,4 full-duplex audio communication circuit 5,6,7 operational amplifier amplifier circuit 8 DC stabilization circuit 9 differential amplifier circuit 9a first input terminal 9b second input terminal 10 , 20 Earphones having transducer and microphone functions 11, 12 Branch circuit 11a First output circuit, resistor circuit 12a First output circuit, impedance circuit 11b, 12b Second output circuit, resistor circuit 13 Impedance circuit (series of resistor and coil Circuit), (series circuit of resistance and capacitance) 200 main body of communication device, main body of portable telephone 200a input terminal for audio transmission signal to other party 200b output terminal for audio reception signal from other party

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2000-138745 (JP, A) JP-A-62-213353 (JP, A) JP-A-50-131705 (JP, A) JP-A-56-93464 (JP, A) Special Table 61-501362 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 3/32 H03F 3/62 H04M 1/58-1/62 H04M 1 / 00-1/23 H04M 1/74-1/78 H04R 3/02

Claims (8)

(57) [Claims] 1. A full-duplex audio communication circuit for use in a handset of a communication device, comprising: a transducer that converts a sound input into an electric transmission signal and simultaneously converts an electric reception signal into a sound output.
r), a differential amplifier circuit for outputting a transmission signal to a transmission amplifier circuit, and a receiving signal from the reception amplifier circuit for branching and connecting to a first input terminal and a second input terminal of the differential amplifier circuit, respectively. A first output circuit of the branch circuit is formed of a resistor circuit, is grounded via a resistor, and is connected to the first input terminal;
The second output circuit is composed of a resistance circuit, is grounded via the transducer, is connected to the second input terminal via a resistor, and the resistor circuit allows a signal from a reception amplification circuit to be connected to the second input terminal of the differential amplification circuit. A full-duplex audio communication circuit wherein the amplitudes of the first input terminal and the second input terminal are the same. 2. A full-duplex audio communication circuit for use in a handset unit of a communication device, comprising: a transducer for converting an acoustic input into an electric transmission signal and, at the same time, converting an electric reception signal into an acoustic output; A differential amplifier circuit for outputting to the transmission amplifier circuit, and a branch circuit for branching a reception signal from the reception amplifier circuit and connecting to a first input terminal and a second input terminal of the differential amplifier circuit, respectively. The first output circuit of the branch circuit is formed of an impedance circuit and is grounded via a resistor, is connected to the first input terminal, and the second output circuit is formed of a resistance circuit and is grounded via the transducer. Connected to the second input terminal via a resistor, and the signal from the receiving amplifier circuit is connected to the first input terminal of the differential amplifier circuit by the impedance circuit and the resistor circuit. A full-duplex audio communication circuit wherein the second input terminals have the same amplitude and the same phase. 3. The full-duplex audio communication circuit according to claim 2, wherein said impedance circuit comprises a series circuit of a resistor and a capacitor. 4. The full-duplex audio communication circuit according to claim 1, wherein said communication device is a portable telephone. 5. The full-duplex audio communication circuit according to claim 1, wherein the transducer is a magnetic earphone, a dynamic earphone, or a crystal earphone having a microphone function. 6. A full-duplex audio communication circuit for use in a handset section of a communication device, comprising: a transducer for converting an audio input into an electrical transmission signal, and simultaneously converting an electrical reception signal into an audio output; A differential amplifier circuit for outputting to the transmission amplifier circuit, and a branch circuit for branching a reception signal from the reception amplifier circuit and connecting to a first input terminal and a second input terminal of the differential amplifier circuit, respectively. A first output circuit of the branch circuit is formed of a resistor circuit, is grounded via an impedance circuit, is connected to the first input terminal, and a second output circuit thereof is formed of a resistor circuit,
Grounded via the transducer and connected to the second input terminal via a resistor, the impedance circuit allows a signal from a receiving amplifier circuit to be coupled to the first and second input terminals of the differential amplifier circuit. A full-duplex audio communication circuit, wherein the amplitude and the phase are the same. 7. The impedance circuit comprises a series circuit of a resistor and a capacitor when the transducer is a crystal earphone, and comprises a series circuit of a resistor and a coil when the transducer is a magnetic or dynamic earphone. The full-duplex audio communication circuit according to claim 6. 8. The full-duplex audio communication circuit according to claim 6, wherein the communication device is a portable telephone.