JPS63299527A - 2-wire/4-wire converting circuit for telephone system - Google Patents

Abstract

PURPOSE:To satisfactorily delete the transmitting speech signal superposed on the receiving speech signal by adding an impedance element equivalent to the input/output of a telephone circuit to a signal system circuit to which the transmitting speech signal is sent and connecting the system path of the receiving speed signal to said impedance element via a resonance circuit having a prescribed resonance frequency. CONSTITUTION:The transmitting speech signals superposed on the receiving speech signals have different levels and phases by the input/output impedances of telephone circuit L1 and L2. The level and the phase of an inverted transmitting speech signal which offsets the transmitting speech signals are coincident with those of the transmitting speech signal by an impedance element Z equivalent to the input/output impedance of the telephone circuit. Thus the transmitting speed signal components are substantially offset to the superposed signals. Under such conditions, however, the transmitting speech signal component remains by a frequency. For this particular frequency, the connection is secured by a resonance circuit RC between the system bus of an inverted signal and that of a received signal. As a result, the levels and phases are coincident with each other between the transmitting speech signal and the inverted signal and both signals are offset completely to each other. Thus the transmitting speech signal superposed on the receiving speech signal is satisfactorily deleted.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention is directed to a transmission signal (
The present invention relates to a 2-wire to 4-wire conversion circuit for a telephone device that eliminates sidetones.

[Conventional technology]

As is well known, current telephone devices use two-wire to four-wire conversion circuits to achieve so-called simultaneous two-way communication, in which calls are sent and received at the same time, using two transmission lines.

A resistive bridge type circuit was used as this 2-wire to 4-wire conversion circuit. A balancing network method and a booster method in which a receiving circuit and a transmitting circuit are connected via a hybrid transformer are known.

Of these, the balancing network method tends to lose its balanced state due to impedance fluctuations, and the transmitting sound tends to go around the receiving circuit, making it difficult to obtain good call performance. there were.

On the other hand, in the hybrid method, a signal with one phase inverted is added to the transmitting signal from the transmitting circuit that is currently being routed to the receiving circuit to cancel it out, thereby suppressing the sidetone output from the receiver. Suggestions have been made to try to prevent this.

For example, a transmitting signal output from a telephone receiver is inputted to an inverting input terminal of a differential amplifier interposed between the lines, a receiving system circuit, and the telephone receiver.

The output from the receiving system circuit, that is, the superimposed signal of the receiving signal from the line and the transmitting signal that has passed around to the receiving system circuit is input to the non-inverting input terminal of the differential amplifier, and the signal is transmitted from among this superimposed signal. One idea is to cancel and remove the speech signal component and send only the received signal to the handset, which can provide a relatively stable side sound protection effect.

(Problem to be solved by the invention) However, even if the above-mentioned hybrid type 2-wire to 4-wire conversion circuit is not a balancing network system, it is still difficult to connect the lines depending on the length and shortness of the line, selection of special numbers, etc. The side sound protection effect differs depending on the input/output impedance of the terminal and the frequency of the transmitting signal, and high-quality calls may not be obtained.

In other words, the level and phase of the transmitting signal that goes around the receiving circuit changes depending on its frequency and the difference in the input and output impedance of the lines, but on the other hand, the transmitting signal is input to the inverting input terminal of the differential amplifier. Since the transmitting signal always has a constant level and phase regardless of the above fluctuation factors, a mismatch in phase and level will occur between the two signals. For this reason, there was a problem in that the differential amplifier could not sufficiently cancel out the two signals, and a good side sound prevention effect could not be obtained.

This system No. 11 was developed by focusing on the above-mentioned problem, and can sufficiently remove the transmitting signal that goes around to the receiving system circuit and is superimposed on the receiving sound signal, and achieves a good side sound prevention effect. The present invention aims to provide a 2-wire to 4-wire conversion circuit for a telephone device that can be obtained.

[Means for solving problems]

The present invention provides a 2-wire to 4-wire conversion circuit for a telephone device that adds a transmitting signal whose phase is inverted to the superimposed signal in order to cancel the transmitting sound signal superimposed on the received signal.
An impedance element equivalent to the input/output impedance of a telephone line is provided in a signal system circuit to which the transmitting signal whose phase is inverted is sent, and a signal system circuit for this inverted signal and a signal system path for the receiving signal are set in a predetermined manner. They are connected via a resonant circuit having a resonant frequency of .

(Function) In the present invention, the level and phase of the sending signal superimposed on the receiving signal differs depending on the input/output impedance of the telephone line, and the counter-transferring signal that should cancel out the sending signal is also superimposed on the telephone line. Since the level and phase of the impedance element equivalent to the input/output impedance can be matched with the transmitting signal, most of the transmitting signal components are canceled out from the superimposed signal. However, depending on the frequency, there is still a possibility that transmit signal components may remain depending on the frequency. The levels and phases of the signals (the transmitting signal and the inverted signal) are matched, and both signals are completely canceled out.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

Here, a case will be shown in which the 2-wire to 4-wire conversion circuit of this embodiment is applied to a so-called hands-free phone having a sound amplification function.

In the figure, HTl is a first hybrid transformer that connects the telephone lines Ll and L2 with the receiving circuit α and the transmitting circuit β, and A1 is the telephone line Ll.

This receiver amplifier amplifies the receiver signal sent out via L2 and the first hybrid transformer HTI, and its output is input to the non-inverting input terminal of a differential amplifier A3 serving as an adding means. Further, the signal output from the differential amplifier A3 is output to the speaker SP via the amplifier A4.

Further, M is a microphone that inputs the transmitted voice, E is a received voice removing circuit that removes the voice-receiving signal that has entered the microphone M from the speaker SP, and outputs only the voice signal that is transmitted from the speaker, A5 is a receiving amplifier that amplifies the transmitting sound signal output from the receiving sound removing circuit E, and its output is output to two driver amplifiers DI and D2.

RDI and RD2 are output impedance matching resistors for increasing the output impedance of both driver amplifiers DI and D2 to telephone lines Ll and L2 to appropriate values. The transmit signal is input to the amplifier A2, and the transmit signal sent via the resistor RD2 is input to the amplifier AI. Also,
The output terminal of the amplifier A2 is connected to the inverting input terminal of the differential amplifier A3, and the amplifier A2, the differential amplifier A3, and the amplifier AI constitute an instrumentation amplifier. Z is the telephone line Ll, L
24. ) An impedance element having an impedance equivalent to the impedance of the actual telephone line Ll, L2.
It has inductance, capacitance, and resistance approximated by . HT2 is a second hybrid transformer that couples this impedance element 2 and the transmission system circuit β, and has the same configuration as the first hybrid transformer HTI. RC is a series resonant circuit consisting of a coil, a capacitor C, and a resistor R, and is connected to the amplifier AI.

Connected to the input terminal of A2.

The primary effect will be explained based on the above configuration.

The reception signal sent via the telephone lines Ll and L2 is sent to the amplifier A1 via the first hybrid transformer HTI.
is input. At this time, if the caller is inputting the transmitting sound from the microphone M, this transmitting signal passes through the cancellation circuit E, is amplified by the receiving amplifier A5, and is then amplified by the driver amplifier D2 and the first hybrid transformer HTI. The signal is output to the telephone lines LL and L2 via the driver amplifier DI and the amplifier A2, and is input to the inverting input terminal of the differential amplifier A4 via the driver amplifier DI and amplifier A2. Also, driver amplifier D
A portion of the transmitting signal sent out from A2 is superimposed on the received signal and input to the amplifier AI, where it is amplified and then input to the non-inverting input terminal r of the differential amplifier A3. and,
The differential amplifier A3 calculates the difference between the IIf signal of the receive signal and the transmit signal input to the non-inverting input terminal and the transmit signal input to the 1-inverting input terminal (1), in other words, the phase of the superimposed signal. Outputs the sum with the inverted transmission signal.

Here, when comparing the sending signal component St included in the superimposed signal with the sending signal S2 input to the inverting input terminal, the signal S1 is affected by the characteristic impedance of the telephone lines Ll and L2, and its signal level is However, the signal S2 is also attenuated in the same way as the signal Sl due to the influence of the impedance element Z equivalent to the telephone lines Ll and L2 in the signal path, and both signals S
t.

S2 is at the same level. Therefore, in differential amplifier A3,
! The signal component Sl included in the rfffl signal S2 is canceled by the signal S2, and as a result, only the received signal is output to the subsequent amplifier A4.

However, the frequencies of the transmission signals Sl and S2 are 30011z~8.
00! If it is within the range of Iz, 1 yen upper number Sl.

Since a phase difference inevitably occurs in S2, even if the signals Sl and S2 are input to the differential amplifier A3 in this state, a sufficient canceling effect cannot be obtained.

Therefore, in this embodiment, the resonant frequency of the resonant circuit RC is set to a value between 30 Q It z and 80011 z, and the selectivity is adjusted to significantly affect the receiving sound quality! To the extent that F does not occur: Both sending signals S1. It is now possible to approximate the phase and signal level of S2. As a result, the transmitting signal S1 that goes around to the receiving system circuit α is transmitted at a signal frequency]0
Although it is possible to almost completely eliminate the signal from 011z to 40011z, some residual canceled signal may still be included in the received signal.

For this reason, in this embodiment, impedance matching resistors RDI and RD2 are provided at the output terminals of the transmitting driver amplifiers DI and D2 to reduce the residual rate of the canceling remaining signal with respect to the receiving signal, thereby increasing the efficiency of receiving the receiving signal. It's supposed to increase.

That is, by providing the resistors RDI and RD2, the output impedance of the transmitting driver amplifiers DI and D2 increases, and the attenuation rate of the input receiving signal decreases. As a result, the amplification factors of the amplifiers AI and A2 can be set lower by the reduction in the attenuation factor, and as a result, only the level of the transmitting signal output from the amplifier AI is reduced, making it possible to obtain better speech performance. . In addition, in the above explanation, the case where this invention is applied to a hands-on phone is shown, but this IJ1 can also be applied to other telephone types, and is not particularly limited to the above embodiment. .

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to sufficiently remove the transmitting signal that goes around the receiving circuit and is superimposed on the received signal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. Ll, L2...Telephone line

Claims (1)

[Claims] The transmitting signal outputted from the transmitting voice input means is outputted to the telephone line, and the phase of the transmitting signal is inverted, and the inverted signal is superimposed on the received signal by the adding means to form the inputted transmitting signal. In addition, the 2-wire to 4-wire conversion circuit of the telephone device is configured to output the incoming voice sound to the receiving sound output means, and an impedance element equivalent to the input/output impedance of the telephone line is provided in the signal path through which the inverted signal is sent. A 2-wire to 4-wire conversion circuit for a telephone device, characterized in that the signal path of the inverted signal and the signal path of the received call signal are connected via a resonant circuit having a predetermined resonant wave number.