JP3065613U - Full-duplex audio communication circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable circuit which requires only one transducer and has no electric feedback in a full-duplex audio communication circuit using a transducer such as an earphone having a microphone function. SOLUTION: An impedance circuit for matching the amplitude and phase at each input terminal of a differential amplifier circuit is provided so that a received signal is not electrically fed back to a transmission side.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a full-duplex audio communication circuit used in a handset unit of a communication device, a wireless transceiver, a mobile phone, and the like. Particularly, 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 a single transducer without using a transmitter and a receiver separately.

[0002]

[Prior art]

 Full-duplex communication has advantages over half-duplex communication because both parties can make and receive calls simultaneously.

However, full-duplex communication is a closed loop circuit for transmitting and receiving at the same time. The total loop gain must be less than 1 so that there is no feedback there. This type of device usually had separate speakers and microphones.

[0004] US Pat. No. 4,002,860 provides a method for solving the audio feedback problem. The communication device described in the patent uses a speaker and a transducer for canceling audio feedback. 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 will be described as a portable telephone main body, and the transducers 101 and 102 will be described as earphones having a microphone function.

[0006] This 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 an operational amplifier circuit 103, amplified, and then transmitted to the operational amplifier circuits 104 and 105, respectively. input. These amplified outputs enter the differential amplifier circuit of the operational amplifier circuit 106.

Since the input signal of the operational amplifier circuit 106 has the same amplitude and phase, its output signal is canceled, and at the same time, the received signal becomes an acoustic output from each of 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, as for the voice to be transmitted, the transducers 101 and 102 detect vibrations in the respective ears (air vibrations of the inner ear) and convert them into audio signals. These audio signals are input to operational amplifier circuits 104 and 105, respectively, and amplified. Here, since the polarities of the transducers 101 and 102 are set in advance to 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, by using the transducers 101 and 102, the cancellation amount of the electric signal feedback is reduced to −40 db or less by the cancellation circuit in which the component of the reception signal R in the transmission signal S is canceled. did.

[0011]

[Problems to be solved by the invention]

 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 two required were very cumbersome.

A second drawback is that the cancellation circuit of FIG. 6 requires that each circuit constant of the cancellation circuit be set accurately in order to reduce the amount of electrical signal feedback cancellation to -40 db or less. is there. 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 the constant, even if it 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.

The present invention has been made in view of the above points, and has as its object the purpose of using only one earphone having the function of a transducer, ie, a microphone, and to provide a complete canceling circuit that operates stably. It is to provide a dual audio communication circuit.

[0016]

[Means for Solving the Problems]

 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. A transducer (Transducer) which is a magnetic earphone, a dynamic earphone, or a crystal earphone having a microphone function for converting a signal into an acoustic output, a differential amplifier circuit for outputting a transmission signal to a transmission amplifier circuit, and reception from a reception amplifier circuit. A branch circuit for branching a signal and connecting to a first input terminal and a second input terminal of the differential amplifier circuit, respectively, wherein the first output circuit of the branch circuit comprises a resistor circuit and is grounded via a resistor; At the same time, when the second output circuit is connected to the first input terminal and the second output circuit is formed of a resistor circuit and is grounded via the transducer, Both are connected to the second input terminal via a resistor, and the resistance circuit makes the signal from the receiving amplifier circuit have the same amplitude at the first input terminal and the second input terminal of the differential amplifier circuit. I do.

A full-duplex audio communication circuit used in a handset of a communication device, the magnetic circuit having a microphone function of converting a sound input into an electric transmission signal and simultaneously converting an electric reception signal into a sound output. A transducer that is an earphone, a dynamic earphone, or a crystal earphone, a differential amplifier that outputs a transmission signal to a transmission amplifier, a reception signal that is branched from the reception amplifier, and a first input terminal of the differential amplifier. And a branch circuit for connecting to the second input terminal. The first output circuit of the branch circuit is formed of an impedance circuit, is grounded via a resistor, and is connected to the first input terminal. The output circuit comprises a resistor circuit, which is grounded via the transducer, and connected to the second input terminal via a resistor. And, said impedance circuit and the first input terminal and the respective amplitudes same at the second input terminal of the signal from the receiving amplifier circuit by the resistor circuits the differential amplifier circuit, characterized in that the phase-phase.

Further, the impedance circuit according to claim 2 is characterized by comprising a series circuit of a resistor and a capacitor.

A full-duplex audio communication circuit for use in a handset of a communication device, comprising: a transducer for converting an acoustic input into an electric transmission signal and simultaneously 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 a resistor circuit and is grounded via an impedance circuit, and is connected to the first input terminal. The second output circuit is formed of a resistor circuit and is grounded via the transducer. Connected to the second input terminal via a resistor, and a signal from a reception amplifier circuit is connected to the first input terminal of the differential amplifier circuit by the impedance circuit. Respectively, characterized that you amplitudes same, the phase-phase in a force terminal and the second input terminal.

Further, the impedance circuit according to claim 4 comprises a series circuit of a resistor and a capacitor when the transducer is a crystal earphone, and a series of a resistor and a coil when the transducer is a magnetic earphone or a dynamic earphone. It is characterized by comprising a circuit.

A full-duplex audio communication circuit, wherein the communication device according to claim 1, 2, 3, 4, or 5 is a portable telephone.

[0022]

[Embodiment of the invention]

 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 in the first embodiment, both are resistance circuits. Reference numeral 10 denotes a transducer, an earphone having a microphone function, 9 denotes a differential amplifier circuit, 9a denotes a first input terminal, and 9b denotes a second input terminal. Here, the first output circuit 11a is connected to a first input terminal 9a, and the second output circuit 11b is connected to an earphone 10 having the configuration of the microphone, and a second input circuit is connected via a resistor. It is also connected to terminal 9b. 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 section of the communication device main body 200, is output from its output terminal 200b, passes through a filter circuit for attenuating high frequency components and the like, is amplified by operational amplifier amplifier circuits 5, 6, and is branched. Input to the circuit 11. Here, the received signal R is input to the earphone 10 having a microphone function via the second output circuit 11b, and the 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 9 a and the second input terminal 9 b is output to the output terminal of the differential amplifier circuit 9, but the amplitude of the input of the received signals is the same. If the resistance values of the first output circuit and the second output circuit are determined as follows, the received signal R becomes 0 at the output terminal of the differential amplification circuit 9. Thus, there is little electrical feedback.

On the other hand, the sound is detected by the earphone 10 having a microphone function by 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 9 b of the differential amplifier circuit 9. , And becomes the transmission output S.

Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment shown in FIG. 2 is obtained by further improving the electric feedback of the first embodiment shown in FIG.

As can be understood 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 such an inductance component is present, the second input terminal 9 b of the differential amplifier circuit 9 is formed by the inductance component of the transducer 10 which is in parallel with the second output circuit 11 b or 12 b of the branch circuit 11. Of the received signal R at the first input terminal 9a 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, 12a denotes an impedance circuit as a first output circuit, and 12b denotes a resistance circuit as a second output circuit.

The impedance circuit 12a is a circuit for adjusting the phase shift of the received signal due to the inductance component. Because the phase of the received signal at the second input terminal 9b of the differential amplifier circuit 9 is advanced from the phase of the received signal at the first input terminal 9a due to the inductance component of the transducer 10, the phase of the received signal at the first input terminal 9a is reduced accordingly. What is necessary is just to make it the impedance circuit 12a which advances. FIG. 3B 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, even if the inductance component cannot be ignored in the transducer 10 by the impedance circuit 12a of the second embodiment, this effect is canceled and the reception signal R on the output side of the differential amplifier circuit 9 is completely set to zero. Therefore, electrical feedback can be stably suppressed.

The effect of canceling the effect of the inductance component will be described in more detail. 2 and 3, the voltage at the output point of the operational amplifier 6 (the branch point of the branch circuit 12) is represented by e._RAnd the voltage at the connection point between the second output circuit (resistor circuit) 12b and the transducer 10 is denoted by e._MAnd the voltage at the connection point between the first output circuit (impedance circuit) 12a and the resistor R9 is denoted by e._AAnd Further, it is assumed that the resistance of the second output circuit 12b is R0, and the resistance R0 is connected to the input terminal 9b of the differential amplifier circuit 9 via the resistance R1. However, it is assumed that R1 >> R0. Here, if angular frequency ω = 2πf (f: frequency) and j = √ (−1), e _M And e_RIs given by the following equation. K1 = (e_M/ E_R) = (R + jωL) / {(r + R0) + jωL} (1) Here, when ω is large, K1 → 1. When ω is small, K1 = r / (r + R0), which is a value close to 0. That is, e_MIs almost proportional to the angular frequency ω as can be understood from the equation (1). On the other hand, e_AIs e_MIf the amplitude and the phase do not match, the output of the differential amplifier 9_RSince no minutes are output, e_AMust also be proportional to ω. Therefore, the capacitance C must be connected in series to the impedance circuit 12a. That is, 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), and if R9 >> R, K2 → 1. When ω is small, K2 → 0. Therefore, since both are proportional to the angular frequency ω, if a constant is selected, the same amplitude should be applied to both input terminals 9a and 9b of the differential amplifier 9 with respect to the angular frequency ω with the same frequency characteristics. Can be. Therefore, e_RIs canceled. FIG. 4 shows a full-duplex audio communication circuit 3 of another embodiment. In this embodiment, an impedance circuit 13 including a resistor r 'and a coil L' is provided in place of R9 of the full-duplex audio communication circuit 2 of the embodiment shown in FIG. Now, if R1 >> R0, R0 = R, and L '= L, r' = r, then (r + jωL) / {(r + R0) + jωL} (r '+ jωL') / ｛(r '+ R) + JωL ′｝, and e_M≒ e_AAnd the signal is canceled with the same phase and the same amplitude._RThe ingredients are gone. FIG. 5 shows a full-duplex audio communication circuit 4 of still another embodiment. In this example, the transducer 20 is a crystal earphone (piezo earphone). As shown in FIG. 5, the circuit becomes capacitive. Where C_MAnd r_MIs an equivalent circuit of a crystal earphone. To cancel this, as shown in FIG._MAnd r ' _M Is required. As in the case of FIG. 4, assuming that R1 >> R0 and R0 = R, C '_M= C_M, R '_M = R, then e_M≒ e_AAnd almost the same phase and the same amplitude are cancelled._RThe ingredients are gone.

[0034]

[Effect of the invention]

 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 trouble for the ear is greatly reduced. effective. (2) Even if the inductance or capacitance component of an earphone or the like that has the function of a microphone cannot be ignored, this effect is negated and full-duplex audio communication that operates stably without complete electrical feedback can be performed. There is.

[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 the 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 according to the present invention;

FIG. 5 is a block diagram of a fourth embodiment of the 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 Transducer, earphone having microphone function 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 the other party 200b output terminal for audio reception signal from the other party

Claims (6)

[Utility model registration claims] 1. A full-duplex audio communication circuit for use in a handset of a communication device, the microphone having a microphone function of converting an audio input into an electric transmission signal and simultaneously converting an electric reception signal into an audio output. A transducer that is an earphone, a dynamic earphone, or a crystal earphone, a differential amplifier that outputs a transmission signal to a transmission amplifier, and a reception signal that is branched from a reception amplifier. A branch circuit for connecting to an input terminal and a second input terminal, wherein the 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 of a communication device, the magnetic circuit having a microphone function of converting a sound input into an electric transmission signal and simultaneously converting an electric reception signal into a sound output. A transducer that is an earphone, a dynamic earphone, or a crystal earphone, a differential amplifier circuit that outputs a transmission signal to a transmission amplifier circuit, a receiving signal from the reception amplifier circuit, and a first input terminal of the differential amplifier circuit. A branch circuit for connecting to a second input terminal, wherein a first output circuit of the branch circuit is formed of an impedance circuit, is grounded via a resistor, is connected to the first input terminal, and has a second output circuit. The circuit comprises a resistor circuit, which is grounded via the transducer, connected to the second input terminal via a resistor, Impedance circuit and respective amplitudes same in the signal from the receiving amplifier circuit by the resistor circuits first input terminal and the second input terminal of said differential amplifier circuit, full-duplex audio communication circuit, characterized in that the phase-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. A full-duplex audio communication circuit for use in a handset section 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 a resistor circuit and is grounded via an impedance circuit, and is connected to the first input terminal. The second output circuit is formed of a resistor 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 connected to the first input terminal of the differential amplifier circuit by the impedance circuit. A full-duplex audio communication circuit wherein the second input terminals have the same amplitude and the same phase. 5. 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 4. 6. The full-duplex audio communication circuit according to claim 1, wherein said communication device is a portable telephone.