JP3064555U - Full-duplex audio communication circuit - Google Patents

Abstract

(57) Abstract: In a full-duplex audio communication circuit using a transducer such as an earphone having a microphone function, high-performance full-duplex audio communication that eliminates electrical feedback and may use only one transducer. Provide a circuit. A high-speed changeover switch is provided on an audio reception line and a transmission line, and transmission / reception signals are simultaneously sampled and transmitted / received in a time-division manner.

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. In particular, the present invention relates to a full-duplex communication circuit using a transducer having a function of converting sound into an electric transmission signal and simultaneously converting an electric reception signal into sound.

[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 transducer that serves as both a speaker and a microphone 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, the transducers 101 and 102 detect the sound to be transmitted by the transducers 101 and 102 and convert them into audio signals. These audio signals are input to operational amplifier circuits 104 and 105 and amplified. Here, the polarities of the transducers 101 and 102 are set in advance to the opposite polarities, so that 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 device main body 200 as a transmission output S, where it is FM-modulated and becomes a carrier signal and is radiated from the antenna.

As described above, by using the transducers 101 and 102, the cancellation and amount of the electric signal feedback can be 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. And

[0011]

[Problems to be solved by the invention]

 However, the method for improving the electrical feedback as shown in FIG. 4 has the following problems.

First, the first drawback is that the circuit constants of the cancel circuit shown in FIG. 4 must be accurately set in order to reduce the amount of electric signal feedback cancel to −40 db or less. . If each circuit constant has a shift or movement of the constant, even if it is slightly smaller than the set value, there is a disadvantage that the cancellation amount is sharply reduced.

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

A second drawback is that two earphones as transducers are required. That is, the transducer must be placed in both ears.

The present invention has been made in view of the above points, and aims at (1) a cancel circuit that performs a stable operation, and (2) an earphone having a function of a transducer or a microphone. An object of the present invention is to provide a full-duplex audio communication circuit that requires only one unit.

[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 for converting a signal into an acoustic output; a first analog switch circuit provided on a transmission signal line connected to the transducer; and a second analog switch circuit provided on a reception signal line connected to the transducer. An analog switch circuit; a first pulse generation circuit for turning on / off the first analog switch circuit at a cycle corresponding to a repetition frequency equal to or higher than an audible frequency and a duty cycle of 50% or less; The second analog switch circuit is OFF when the first pulse is ON, and the duty cycle is OFF when the first pulse is OFF. A second pulse generating circuit having the same cycle as the cycle that is turned on at 50% or less, wherein the audio transmission and reception signals are sampled in a time division manner by the first and second pulses, respectively, and high-speed switching is performed. And can be transmitted and received.

Further, a first audio amplifier circuit to which a transmission signal is input from the transducer via the first analog switch circuit, and an amplification of the first audio amplifier circuit by an ON signal of the second pulse A fourth analog switch circuit for reducing the frequency, a sample and hold circuit provided between the first audio amplifier circuit and a second audio amplifier circuit for inputting and amplifying the transmission signal output thereof, And a third analog switch circuit that causes the sample-and-hold circuit to hold the immediately preceding transmission signal in response to the pulse OFF signal.

Further, the communication device is a portable telephone.

Further, the transducer is a magnetic earphone, a crystal earphone, or a dynamic earphone having a microphone function.

Further, the first and second analog switch circuits are constituted by MOS type FETs or MOS type ICs.

The first pulse generation circuit and the second pulse generation circuit each include a shift register including a plurality of D-type flip-flop circuits, a clock pulse generation circuit for driving the shift register, and a V1 pulse extracted from the rest register. It is characterized by comprising an output circuit and a V2 pulse output circuit.

[0022]

[Embodiment of the invention]

 One embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of a full-duplex audio communication circuit 1 according to the present invention. First, the flow of the reception signal R and the transmission signal S in the full-duplex audio communication circuit 1 of FIG. 1 will be described.

The received signal R, which is an audio signal demodulated by the receiving unit of the communication device main body 200, passes through a smoothing circuit 23 for attenuating high frequency components and the like, and is input to an operational amplifier circuit 23. The output is input to the transducer 10 via the second analog switch circuit 12, converted into sound and output.

Here, the second analog switch circuit 12 is turned ON / OFF by the second pulse V ₂ generated from the second pulse generation circuit 16. At the same time, the fourth analog Gusuitchi circuit 14 also ON · OFF by the second pulse _{V 2.}

On the other hand, the audio input is converted into an audio signal by the transducer 10 and is input to the operational amplifier circuit 18 (first audio amplification circuit) via the first analog switch circuit 11. The output of the operational amplifier circuit 18 is input to the operational amplifier circuit 19 (second audio amplifier circuit) via the sample and hold circuit 24. The output of the operational amplifier circuit 19 passes through a smoothing circuit 22 that attenuates high-frequency components and the like, and is sent as a transmission signal S, which is an audio signal, to a transmission unit of the communication device main body 200.

Here, the first analog switch circuit 11 is turned ON / OFF by the first pulse V ₁ generated from the first pulse generation circuit 15. To ON · OFF by the third analog switch circuit 13 first pulse _{V 1} at the same time.

Next, the operation of the full-duplex audio communication circuit 1 of FIG. 1 will be described.

The first and second pulse generation circuits 15 and 16 output first and second pulses V ₁ and V ₂ , respectively, and their pulse cycle is 10 μs (repetition frequency 100 KHz). The duty cycle of each pulse is 50% or less, and the ON / OFF phases of the pulses are opposite phases as shown in FIG.

Therefore, when the first and third analog switch circuits 11 and 13 are ON, the second and fourth analog switch circuits 12 and 14 are OFF, and when the former is OFF, the latter is OFF. Becomes ON.

As described above, the pulse generation circuits 15 and 16 and the analog switch circuits 11 to 14 operate, so that the reception signal R from the reception section of the communication device main body 200 is amplified by the operational amplifier circuit 17 and then the audio signal R is amplified. Is sampled by the second analog switch circuit 12 every 10 μs with a _second pulse V ₂ having a pulse width of 1 μs or less during the ON period. The sampled audio signal is converted into sound by the transducer 10, and the sound is output. At this time, since the sampling frequency is 100 KHz, it cannot be heard because it is sufficiently higher than the audible frequency of the ear.

Here, during the period of the first pulse V ₁ OFF and the second pulse V ₂ ON, the fourth analog switch circuit 14 is turned ON, the resistance R of the operational amplifier circuit 18 is reduced, and the amplification is suppressed. At the same time, the third analog switch circuit 13 is turned off, the signal is held in the capacitor C, and the sample-and-hold circuit 24 is formed as shown in the figure. Make sure that the previous signal is being input.

On the other hand, the sound is converted into an audio signal by the transducer 10 by detecting the vibration at the ear as a sound input, and the transmission signal is converted into a first pulse having a pulse width of 1 μs or less during the ON period by the first analog switch circuit 11. It is sampled to 10μs each in V _1. The sampled audio signal is input to the operational amplifier circuit 18.

Here, during the period of the first pulse V ₁ ON and the second pulse V ₂ OFF, the fourth analog switch circuit 14 is turned off and the third analog switch circuit 13 is turned on. At 18, the audio signal is amplified, input to the next operational amplifier circuit 19, and amplified. The output is attenuated by a smoothing circuit 22 at a sampling frequency of 100 KHz, and is sent as an audio transmission signal S to a transmission section of the communication apparatus main body 200.

As is apparent from the above operation, an operation period in which the received signal R from the communication device main body 200 is converted by the transducer 10 to be an audio output, and an audio input is converted by the transducer 10 to be transmitted signal The operation period sent to the communication device main body 200 as S is completely different.

In other words, the first pulse V ₁ and the second pulse V ₂ alternately switch at a period corresponding to a frequency sufficiently higher than the audio frequency, so that reception and transmission are performed in a time-division manner and in separate periods. There is no electrical feedback.

Next, FIGS. 2 and 3 show detailed circuit diagrams of one embodiment of the full-duplex audio communication circuit 2 of the present invention. Here, FIG. 3 is a divided pulse generator circuit 50 when generating the first pulse V ₁ and the second pulse V ₂ of the full-duplex audio communication circuit 2 of FIG.

Hereinafter, the operation of the full-duplex audio communication circuit 2 will be described with reference to FIGS.

First, the operation of the time-division pulse generating circuit 50 shown in FIG. 3 will be described.

Reference numeral 52 denotes a shift register composed of ten D-type flip-flops (delayed flip flops).

The shift register 52 operates with the clock pulse Cp of the clock pulse generation circuit 51. The clock pulse Cp has a frequency of 1 MHz and a period of 1 μs in this example.

Reference numeral 53 denotes a circuit for outputting the first pulse V _1, and reference numeral 54 denotes a circuit for outputting the second pulse V ₂ . The state is shown in FIGS. 3 (a), 3 (b) and 3 (c). (A) is a clock pulse Cp, (b) is a first pulse V ₁ , and (c) is a second pulse V ₂ . In the period of the pulse V ₁ and pulse V ₂ and each 10 [mu] s pulse width 1 [mu] s, their output phase is reversed phase, whereby it is possible to perform time-divided received signal operation and transmit signal operation. In the example shown in FIG. 3, the duty cycle of the pulses V ₁ and V ₂ is 10%.

Returning to FIG. 2, the operation of the full-duplex audio communication circuit when the time-division pulse generation circuit 50 outputs the first and second pulses V ₁ and V ₂ will be described.

The reception signal R of the communication output from the communication device or the receiving unit of the mobile phone main body 200 passes through a switch circuit surrounded by a broken line as shown in FIG. I do. Wherein the switch circuit is a circuit for transmitting a received signal R to the operational amplifier circuit 17 only when the second pulse V ₂ is applied to output from the divided pulse generator circuit 50 when, necessarily switch circuits requiring Absent. Its output is ON · OFF the MOS-type FET12 in the second pulse _{V 2} to be output from the divided pulse generator circuit 50 when. When the MOS FET 12 is ON, the earphone 10 having the function of a microphone is driven to output sound.

On the other hand, the voice of the call is converted into an electric audio signal by detecting the vibration transmitted from the ear with the earphone 10 having a microphone function. This output MOS type FET11 is, when the input to the first pulse _{V 1} operational amplifier circuit 18 in the period in which the ON by the output from the divided pulse generator circuit 50. The MOS FET 14 is an ON / OFF switch for setting the ON state while the received signal R is being output as sound and for suppressing the amplification of the operational amplifier circuit 18 as described above. During the period when the output signal R is being output as a sound, the sample and hold circuit 24 for holding the previous signal is formed as described above while the output signal is in the OFF state. Therefore, the adverse effect of the sampling of the transmission signal S is reduced.

The output of the operational amplifier circuit 18 enters the operational amplifier circuit 19, passes through the operational amplifier circuit 20 for smoothing the audio transmission output sampled at 100 KHz, and the transmission signal S is transmitted to the transmission section of the portable telephone main body 200. Sent to

Note that the operational amplifier circuit 21 is a bias circuit for the operational amplifier circuit power supply.

As described above, the period during which the received signal R from the telephone is amplified to listen to the sound with the earphone 10 having the microphone function, and the sound received by the earphone 10 having the microphone function is amplified to transmit the signal. There is no electrical feedback because the time is completely different from the time when S is sent to the telephone body. The sampling frequency at that time is also 100 KHz (period 10 μs), which is sufficiently higher than the audible frequency, and this sampling frequency can sufficiently cope with the audio signal so as not to adversely affect it.

[0048]

[Effect of the invention]

 The full-duplex audio communication circuit of the present invention has the following effects. (1) The audio transmission and reception are performed in completely different periods by the first and second pulses for time division, and the switching, that is, the sampling frequency is sufficiently higher than the audible frequency. The effect is that full-duplex audio communication can be performed without the need. (2) Conventionally, two earphones, that is, transducers, were required and were troublesome to the ears. However, the present invention requires only one transducer, and has the effect of reducing troublesomeness to the ears.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a full-duplex audio communication circuit of the present invention.

FIG. 2 is a circuit diagram of an embodiment of the full-duplex audio communication circuit of the present invention.

FIG. 3 is a circuit diagram of an embodiment of a time-division pulse generating circuit of the full-duplex audio communication circuit of the present invention.

FIG. 4 is a diagram showing a conventional full-duplex audio communication circuit.

[Explanation of symbols]

Cp clock pulse R reception signal S transmission signal V ₁ first pulse V ₂ second pulse 1, full-duplex audio communication circuit of the present invention 10 earphone having transducer and microphone functions 11 first analog switch circuit, MOS type FET 12 Second analog switch circuit, MOS type FET 13 Third analog switch circuit, MOS type FET 14 Fourth analog switch circuit, MOS type FET 15 First pulse generation circuit 16 Second pulse generation circuit 17, 20, 21 Operational amplifier circuit 18 First audio amplifier circuit, operational amplifier circuit 19 Second audio amplifier circuit, operational amplifier circuit 22, 23 Smoothing circuit 24 Sample hold circuit 50 Time division pulse generation circuit 51 Clock pulse generation circuit 52 Shift register 53 V ₁ pulse output Road 54 V ₂ pulse output circuit 200 main communication unit, a portable telephone body

Claims (3)

[Utility model registration 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 first analog switch circuit provided on a transmission signal line connected to the transducer, a second analog switch circuit provided on a reception signal line connected to the transducer, and the first analog switch The circuit has a cycle equivalent to a repetition frequency equal to or higher than the audio frequency, and a duty cycle of 5
A first pulse generation circuit that turns on and off at 0% or less; and a second analog switch circuit, which is off when the first pulse is on, and duty when the first pulse is off. A second pulse generation circuit having the same cycle as the cycle that is turned ON at a cycle of 50% or less, a first audio amplifier circuit to which a transmission signal is input from the transducer via the first analog switch circuit; A fourth analog switch circuit for reducing the amplification of the first audio amplifier circuit by an ON signal of a second pulse; a second audio circuit for inputting and amplifying the first audio amplifier circuit and its transmission signal output A sample-and-hold circuit provided between the amplifier and the amplifier, and the sample-and-hold circuit converts the immediately preceding transmission signal by an OFF signal of the first pulse. And a third analog switch circuit for storing the audio transmission and reception signals, wherein the audio transmission and reception signals are sampled in a time-division manner by the first and second pulses, respectively, so that transmission and reception can be performed by high-speed switching. Audio communication circuit. 2. The full-duplex audio according to claim 1, wherein the communication device is a portable telephone, and the transducer is a magnetic earphone, a crystal earphone, or a dynamic earphone having a microphone function. Communication circuit. 3. The first and second analog switch circuits are composed of a MOS FET or a MOS IC. The first pulse generation circuit and the second pulse generation circuit are a plurality of D-type flip-flops. a shift register composed of a flop circuit, according to claim 1 or 2, a clock pulse generating circuit for driving it, characterized in that it consists of a V ₁ pulse output circuit and the V ₂ pulse output circuit for taking out from the rest register
A full-duplex audio communication circuit as described.