JP5294918B2 - 2-wire 4-wire conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an electronic circuit has been sophisticated in order to prevent leakage from an output of a radio set to an input of the radio set via a two-wire/four-wire conversion circuit, but it is impossible to prevent the leakage from the output of the radio set to the input of the radio set because its sophistication is insufficient, and malfunction such as oscillation or the like occurs inside the radio set. <P>SOLUTION: A hybrid coupling circuit configured with resistance is used for a two-wire/four-wire conversion circuit and an attenuation between a telephone line and the radio set by this coupling circuit is set to a half or more of an amount which leaks from the output of the radio set to the input of the radio set by this coupling circuit, thereby improving the malfunction such as oscillation or the like in the radio set due to the leakage from the output of the radio set to the input of the radio set. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a 2-wire 4-wire conversion circuit having an input / output terminal (2-wire) for performing bidirectional communication, an output terminal for transmitting a signal, and an input terminal (4-wire) for receiving a signal.

When connecting a radio to a telephone line, the telephone line is configured to be connected to the outside with two lines because it performs two-way communication. Is configured to be connected to the outside with a total of four lines of two lines. Therefore, in order to perform bidirectional communication in this case, it is necessary to provide a 2-wire 4-wire conversion circuit.

FIG. 5 shows a conventional two-wire / four-wire conversion when a radio is connected to a telephone line. As shown in FIG. 5, 2-wire 4-wire conversion was performed using the hybrid transformer T31.

The operating principle of this hybrid transformer T31 is shown in FIG. As shown in FIG. 6, the signal input to port 1 has a characteristic that it is branched to port 2 and port 4 and output, but not output to port 3. The signal input to port 2 has a characteristic that it is branched and output to port 1 and port 3 but not to port 4. Therefore, if port 1 is a 4-wire input terminal 69, port 2 is a 2-wire input / output terminal 61, port 3 is a 4-wire output terminal 68, and port 4 is terminated with the same impedance as the line impedance of port 1 and port 2, the following is performed. To work.

(1) The signal at the 4-wire input terminal 69 is input to the port 1 and appears at the ports 2 and 4, but the signal at the port 4 is erased by the matching circuit 66. Since no signal appears at the port 3, the signal is output only to the 2-wire input / output terminal 61 of the port 2.
(2) The signal at the 2-wire input / output terminal 61 is input to the port 2 and appears at the port 1 and the port 3. Since it is connected to the output side, this signal cannot pass through A31 and stops here. No signal appears at port 4 and appears only at the 4-wire output terminal 68 of port 3.

The two-wire / four-wire conversion is realized by the operations (1) and (2). In principle, the matching circuit 66 of the port 4 can be realized by a resistor having the same value as the line impedance. However, since the telephone line actually has a frequency characteristic, it cannot be perfectly matched only by the resistor. Capacitors are combined to widen the frequency band to match the entire telephone signal.

Further, since the characteristic impedance of the port 3 is halved relative to other ports, a matching transformer (not shown) having an impedance characteristic of 1: 2 may be provided in the port 3 for impedance matching.

In this circuit, one hybrid transformer 65 is indispensable, and a matching transformer (not shown) is required if necessary. However, the hybrid transformer 65 and the matching transformer (not shown) are structurally wide, deep, and high. A certain size is required in each of the three directions, and the circuit cannot be reduced in size. In addition, since the characteristic impedance of the transformer has a large error, the matching circuit 66 cannot completely match and the signal may leak to other ports. In addition, there is a drawback that the material cost and production cost are high and the cost is not reduced.

For this reason, recently, a conversion circuit has been configured by a combination of an amplifying element such as an operational amplifier and a passive element such as a resistor or a capacitor without using the hybrid transformer 65. A block diagram of an example of this conversion circuit is shown in FIG. 1, and its detailed diagram is shown in FIG. In FIG. 1, a coupling circuit (hybrid transformerless) 13 is provided between the radio output 18 and the telephone line input / output 11 so that the radio output 18 is sent to the telephone line input / output 11 side and from the telephone line input / output 11 side. Is received at the radio input 20.

At this time, the following measures are taken in order to prevent the leakage signal X input from the radio output 18 as the radio input 20 via the coupling circuit (hybrid transformerless) 13.
(1) When output as the radio output 18 by the coupling circuit (hybrid transformerless) 13, the phase of the output is inverted by the phase inversion circuit 14. (2) Before the radio output 18 is input to the coupling circuit (hybrid transformerless) 13, a part of the signal is taken out, and the strength (amplitude) of the taken out signal is adjusted by the gain adjustment circuit 15, and the coupling circuit (Hybrid transformerless) Same strength (amplitude) as the crosstalk signal X from 13.

An adder circuit 16 is provided between the phase inversion circuit 14 and the radio input 20, and the adder circuit 16 adds the leakage signal X and the signal from the gain adjustment circuit 15. The two signals cancel each other because they have the same amplitude and are out of phase with each other, and as a result, are not input to the radio input 20. In this way, leakage from the radio output 18 to the radio input 20 via the coupling circuit (hybrid transformerless) 13 is prevented.

Tokusho-3067319

In the above-mentioned system currently in use, it is not possible to completely eliminate the leakage signal caused by the mismatch caused by the difference between the input / output impedance of the wireless device and the line impedance of the relay device or telephone line connected to the wireless device. Since it will be input to the radio, measures are required.

In recent wireless devices, signals (analog signals) input / output to / from the outside are digitally converted inside the wireless device, but in order to perform stable conversion processing, the level of the input signal subjected to analog / digital conversion processing Needs to be smaller than the level of the output signal subjected to the digital / analog conversion processing. If the level of the output signal is greater than the input signal, a countermeasure is necessary because the signal may oscillate within the radio.

In the 2-wire 4-wire conversion circuit for connecting a 2-wire telephone line and a 4-wire radio (two wires for the output of the radio and two wires for the input of the radio), the 2-wire 4-wire The conversion circuit has a hybrid resistance coupling circuit composed of resistors, and the amount of attenuation in the hybrid resistance coupling circuit between the two-wire telephone line and the four-wire radio is a hybrid resistance between the radio output and the radio input. Set it to more than half the amount of leakage in the coupling circuit.

A phase inverting circuit for inverting the phase of the leakage signal from the hybrid resistance coupling circuit; a gain adjusting circuit for adjusting the gain of the radio output signal; and an output signal from the phase inverting circuit and the gain adjusting circuit. The gain adjustment circuit can adjust so that the output signal from the addition circuit is minimized, and the radio output is prevented from leaking to the radio input.

By the above means, it is possible to suppress the leakage signal by reducing the leakage signal generated in the conventional coupling circuit (hybrid transformerless) 2-wire 4-wire conversion circuit. The radio input level can be made smaller than the radio output level, and signal processing within the radio can be performed stably.

Block diagram of a conventional coupling circuit (hybrid transformerless) 2-wire 4-wire conversion circuit Block diagram of 2-wire 4-wire conversion circuit of coupling circuit (hybrid resistor) of the present invention 2-wire 4-wire conversion circuit diagram of conventional coupling circuit (without hybrid transformer) 2-wire 4-wire conversion circuit diagram of coupling circuit (hybrid resistor) of the present invention 2-wire 4-wire conversion circuit diagram using hybrid transformer Operation principle of hybrid transformer

FIG. 2 is a block diagram of a two-wire four-wire conversion circuit using the coupling circuit (hybrid resistor) 25 of the present invention. As shown in FIG. 2, a coupling circuit (hybrid resistor) 25 composed of a resistor is used on the line of the radio output 18.

Here, the level of the radio output 18 is A, and the level of the radio input 20 is B. Let X be the level of the leakage signal X to the radio input 20, and Y be the level of the signal that is attenuated when the signal passes through the coupling circuit (hybrid resistor) 25 of the present invention.

The level A of the radio output 18 in the conventional circuit of FIG. 1 passes through the coupling circuit (hybrid transformerless) 13 and is input to the telephone line input / output 11. Is treated as being not so small that the input level of the telephone line input / output 11 is A. In the telephone line input / output 11, the output level of the telephone line input / output 11 is A because the levels of the input signal and the output signal are assumed to be equal. This is input to the aforementioned coupling circuit (hybrid transformerless) 13 and output to the line of the radio input 20. The signal level at that time is A + X because the leakage signal X from the coupling circuit (hybrid transformerless) 13 is added. Therefore, the level of the radio input 20 is B = A + X.

In the conventional method shown in FIG. 1, since the leak signal X exists, X> 0 and B> A, and if this signal is input to the radio input 20, there is a possibility of oscillation.

On the other hand, in the present invention shown in FIG. 2, the signal level A of the line of the radio output 18 is composed of a resistance hybrid circuit when passing through the coupling circuit (hybrid resistance) 25, so there is signal attenuation by this amount. .

Therefore, the input level of the telephone line input / output 11 is A-Y. As described above, since the input signal level and the output signal level are equal in the telephone line input / output 11, the output level of the telephone line input / output 11 is A−Y, and is input again to the coupling circuit (hybrid resistor) 25 and the radio input 20. Output to the line.

The signal level at that time is obtained by adding the leakage signal X in the coupling circuit (hybrid resistor) 25 to the attenuation in the coupling circuit (hybrid resistor) 25, and (A−Y) + (− Y) + (X) = A + (X -2Y). Here, since X> 0 and Y> 0, if the attenuation amount of the coupling circuit (hybrid resistor) 25 of the present invention is appropriately set, that is, X-2Y <0 is satisfied, B <A, and the wireless device The output signal level becomes smaller than the input signal level, and stable digital / analog conversion processing can be performed.

That is, it is sufficient to satisfy Y> X / 2, and the attenuation setting amount in the coupling circuit (hybrid resistor) 25 may be set to half or more of the leakage amount X in the coupling circuit (hybrid resistor) 25.

Incidentally, the values of the resistors R54, R55, R56, and R57 in the coupling circuit (hybrid resistor) 25 can be determined as follows.
It is assumed that the leakage signal X to the radio input 20 is −4 dB (≈0.63), and the input / output impedance Z of the coupling circuit (hybrid resistor) 25 is 600Ω. Since satisfying Y> X / 2 is a condition for establishing the coupling circuit (hybrid resistor) 25 in the present invention, the resistance value may satisfy Y> 0.63 / 2 = 0.315.

Here, if the square root of the power ratio between the input signal and the output signal of the coupling circuit (hybrid resistor) 25 is K, K is the same as Y. When the values of the resistors R54 and R55 in the coupling circuit (hybrid resistor) 25 are C and the values of R56 and R57 are D, C = Z × | K ² −1 | / 4K = 600 × | 0.315 ² − 1 | / (4 × 0.315) ≈429Ω.
D = Z × | (k + 1) / (k−1) | = 600 × | (0.315 + 1) / (0.315-1) |
≈1152Ω.

Therefore, if the values of R54 and R55 are 429Ω or more and the values of R56 and R57 are 1152Ω or less, the conditions for establishing the coupler in the present invention can be satisfied. In this way, the values of the resistors R54, R55, R56, and R57 in the coupler can be obtained.

FIG. 4 shows a detailed embodiment of the 2-wire 4-wire conversion circuit when the coupling circuit (hybrid resistor) 25 according to the present invention is used. In FIG. 4, the coupling circuit (hybrid resistor) 25 is composed of resistors R54 to R57. A41 is an amplifying circuit which, when connected to the radio output 18, provides a buffer function to prevent the 2-wire 4-wire conversion circuit of the present invention from being affected, and amplifies the radio output 18 Yes.

The output amplified by the amplifier circuit A41 is input to the input terminal 25D of the coupling circuit (hybrid resistor) 25 through the resistor R42 after rotating the signal phase by 180 degrees in the inverting amplifier circuit configured by A42. And that which is directly input to the input terminal 25C of the coupling circuit (hybrid resistor) 25 via the resistor R41.

The radio output 18 input to the hybrid resistance coupling circuit 25 is attenuated by the attenuation determined by the values of the four resistors constituting the coupling circuit (hybrid resistance) 25 and output to the telephone line input / output 11. On the other hand, the output from the telephone line input / output 11 travels in the opposite direction to the above signal and is input to the 25A terminal and 25B terminal of the coupling circuit (hybrid resistor) 25. Since the coupling circuit (hybrid resistor) 25 has reversible characteristics, the coupling circuit (hybrid resistor) 25 is attenuated by the above-described attenuation amount and is output from the 25C terminal and the 25D terminal of the coupling circuit (hybrid resistor) 25 to the resistors R41 and R42. Since it is an amplifier, it is not input to the radio output 18 but proceeds only to the amplifier of A43.

A43 is a differential amplifying circuit. In addition to the two input signals of A43 (this signal is a signal going from the telephone line input / output 11 to the radio input 20 and a signal going from the radio output 18 to the telephone line input / output 11) A part of the signal is branched on the left side of R41 and R42), and the amplitude is equal and the phase is opposite. Therefore, the signal is amplified twice by the differential amplifier circuit A43 and output.

This is amplified by the inverting amplifier circuit configured by A44 and becomes the radio input 20. However, when a part of the output of the inverting amplifier circuit configured by A41 is added to the input signal of the inverting amplifier circuit A44, If the output signal of the differential amplifier circuit is opposite in phase with the amplitude and the amplitude is the same, the output signal of the radio unit mixed at the input of the differential amplifier circuit of A43 can be canceled. In order to adjust the amplitude, an attenuator composed of R43 is provided.

In this specification, it has been described that digital signal processing is performed for a recent wireless device, but a conventional wireless device that directly handles an analog signal can be applied in exactly the same manner. In the description, the wireless device is described as one, but the transmitter and the receiver can be provided separately, and can be applied in the same manner.

11 Telephone line I / O 12 2-line 13 Coupling circuit (without hybrid transformer)
14 phase inversion circuit 15 gain adjustment circuit 16 addition circuit 18 radio output 19 4-wire 20 radio input 25 coupling circuit (hybrid resistance)
61 2-wire input terminal 65 Hybrid transformer 66 Matching circuit 68 4-wire output terminal 69 4-wire input terminals 25A, 25B, 25C, 25D Terminal of coupling circuit (hybrid resistor)
A31, A32 Amplifier circuit A41 Amplifier circuit A42, A44 Inverting amplifier circuit A43 Differential amplifier circuit
R31, R41, R42 Resistor R43 Resistor R54, R55, R56, R57 Resistor T31 Hybrid Transformer Combining a Coupled Circuit (Hybrid Resistor)

Claims (2)

In the 2-wire 4-wire conversion circuit for connecting a 2-wire telephone line and a 4-wire radio (two wires for the output of the radio and two wires for the input of the radio), the 2-wire 4-wire The conversion circuit has a hybrid resistance coupling circuit composed of resistors, and the amount of attenuation in the hybrid resistance coupling circuit between the two-wire telephone line and the four-wire radio is a hybrid resistance between the radio output and the radio input. A two-wire four-wire conversion circuit characterized in that it is set to more than half of the leakage amount in the coupling circuit. 2. The two-wire four-wire converter circuit according to claim 1, further comprising: a phase inverting circuit for inverting the phase of a leakage signal from the hybrid resistance coupling circuit; and a gain adjusting circuit for adjusting a gain of the radio output signal. An adder circuit for adding the output signal from the inverting circuit and the output signal from the gain adjustment circuit; the gain adjustment circuit can be adjusted so that the output signal from the adder circuit is minimized; A 2-wire 4-wire conversion circuit characterized by preventing leakage to the input.