SU1617659A1 - Device for interfacing four-wire and two-wire telephone lines - Google Patents

Abstract

The invention relates to interface devices for four-wire and two-wire communication lines in telephony. The goal is to increase the attenuation of the echo signal with an increased duration of the impulse transient response of the echo path. The four-wire signal in the second low-pass filter 7 and the second high-pass filter 3 is divided by frequency. Its low-frequency components are used to compensate for the echo signals in the echo canceller 10 and, simultaneously with the high-frequency components, are processed in the control unit 12, which controls the passage of the high-frequency components of the device inputs through the differential system 1. f-ly, 2 ill.

Description

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The invention relates to radio engineering and communication and can be used in telephony with high requirements for echo attenuation.

The aim of the invention is to increase the echo attenuation with an increased duration of the impulse transient response.

FIG. Figure 1 shows the electrical circuit diagram of the interface device of a four-wire telephone line with a two-wire; in fig. 2 is a structural electrical circuit of the control unit.

The device contains a differential system 1, the first and second filters 2 and 3 high frequencies, the first and second keys 4 and 5, the first and second filters 6 and 7 low frequencies, the first and second adders 8 and 9, the echo canceller 10, the threshold unit 11, and a control unit 12.

The control unit 12 includes (Fig. 2) two circuits, each of which contains a detector 13, a threshold unit 14, a delay unit 15, a single-oscillator 16, an OR 17 element, an inverter 18 and an And 19 element, a trigger 20 and an additional detector 21 and threshold block 22.

A four-wire telephone line with a two-wire interface works as follows.

In the initial state, in the absence of speech signals, the first key 4 is open, and the second key 5 is closed by the signal of the block 12.

When the subscriber of the four-wire line is talking, a speech signal arrives at the input of the device, which is separated in the second filters 7 and 3, respectively, into the lower and upper frequency bands, which then add up in the second adder 9 and flow through the two-wire line input and output . In this case, the upper frequency band of the original signal passes through the second key 5, which in this mode is in the closed state. At the same time, the lower frequency band of the original signal from the output of the second filter 7 is fed to the second input of the echo canceller 10. The original signal received in the two-wire line It undergoes reflections at the point where the specified line connects to the differential system 1, at various line irregularities, at the point where it is connected to the subscriber unit, and also if the subscriber of this line has a speaker connection in the acoustic path of the specified system.

The reflected source signal in the form of a signal is passed from the input-output to the output of the differential system 1 and further to the inputs of the first filters 2 and 6, in which it is divided

respectively on the upper and lower frequency bands.

Due to the fact that the first key 4 is in the open state, the propagation circuit of the upper echo band 5 is broken.

The lower frequency band of the echo signal is fed to the first input of the echo canceller 10, where it is compensated, which consists in subtracting from it a copy synthesized in the echo canceller 10. To perform this operation, in the echo canceller, the input signals are sampled at a frequency that 15 to be greater than or equal to twice the upper frequency of the lower frequency band of the original signal.

According to the samples obtained at sampling, these 20 values of the coefficients of the impulse response of the lower frequency band of the echo path are calculated, separated from each other by the sampling period adopted in the echo canceller 10.

25 In the echo canceller 10, the echo signal is almost fully compensated, while in the case of the appearance of small residual echo values at its output, the latter are cut off in threshold block 11, which has a large attenuation for small signal levels. Thus, at the output of the device, the echo signal is practically absent. In the event of a subscriber reuse, the four-wire line by the subscriber of the two-wire water speech signal of the latter passes through the input-output and output of the differential system 1, is divided in the first filters 2 and 6, respectively, into the upper and lower frequency bands, the latter passes through 0 the echo canceller 10, the threshold block 11 and the first adder 8 to the input of the device and further to the subscriber of the four-wire line. In addition, the two-wire line subscriber signal comes from the output of the threshold unit 5 11 to the second input of block 12, however, while the four-wire line subscriber speaks, the signal from the output of the second key 5 goes to the first input of block 12, the output signals of the latter, as well as the rsepBoro state and 0 of the second keys 4 and 5 remain unchanged. If the subscriber of the four-wire line stops talking, the signal at the output of the second key 5 and at the first input of block 12 disappears, while its 5 states of the first and second outputs change to opposite, which causes the first key 4 to close and the second key 5 to open. In this case, the upper frequency band of the speech signal of the subscriber's two-wire channel 1, passed through the first key 4, is folded in the first adder 8 with the lower frequency strip of the specified signal and from the device output goes to the subscriber of the four-wire line.

When a subscriber of a four-wire line resumes a conversation, the lower frequency band of his speech signal passes through the second filter 7, the second input and output of the second adder 9, as well as the input and input-output of the differential system 1 to the two-wire line and further to the subscriber. The signal from the output of the second filter 7 also goes to the third input of block 12. However, while at its second input there is a signal coming from the output of the threshold block 1 T, the output signals of block 12, as well as the state of the first and second keys 4 and 5 remain unchanged. When a subscriber terminates a two-wire call, the signal at the output of the threshold unit 11 disappears, and after a certain delay time equal to several hundred milliseconds it changes to opposite sides of the signals at the first and second outputs of the block 12 and, the state of the first and second keys 4 and 5 so that the first of them is open and the second is closed. The signal paths in this case correspond to those described above. The delay in block 12 prevents false switching of keys 4 and 5 during pauses in the conversation of a two-wire subscriber, when the signal at the output of the threshold unit 11 is absent, and at the output of the second filter 7 still continues, for example, due to acoustic 3 reverberation at the subscriber four-wire line.

Block 12 works as follows. In the initial state, trigger 20 is in one of two possible states — 4 scientific research institutes. For example, one in which the signal 1 is present at the first output, and the signal at the second output - O. This state corresponds to the closure of the first switch 4 and the opening of the second switch 5 of the device.

In the case of a four-wire subscriber, a speech signal is sent to the third input of block 12, which after detection in an additional detector 21 is fed to the input of an additional 50 threshold block 22. When the threshold signal of the specified block is exceeded, the signal G appears -the first input element And 19 of the second circuit. If at that time the subscriber of the two-wire line is talking, the speech signal of the latter is fed to the second input of the block 12, detected in the detector 13 of the second circuit, is compared with the threshold value in the threshold block 14

 5 10 5 0

of this circuit and in case of its excess in the form of 1, it enters the input of block 1B and the inverse input of the one-shot 11 of the same circuit the inverter 18 is O and the output of the element AND 19 of the second circuit is O. The state of the trigger 20 in this case does not change.

When a subscriber terminates a two-wire call, the signal at the second input of block 12 disappears, which leads to the appearance of O at the output of the threshold block 14 of the second circuit, and this causes the one-vibrator 16 to trigger in it. At the output of which T appears for a while the time interval defined by the delay of block 15 at the first input of the element OR 17 of the second circuit appears O, but the output state of this element does not change until the end of the supply of G from the output of the one-shot 16. At the end of the output pulse of the one-shot 16 n the second input of the element OR 17 appears O, the output of the specified element also appears O, the output of the inverter 18 - G, which leads to the appearance of 1 at the output of the element And 19 of the second circuit and to the switching of the trigger 20, the first output of which is O, and the second is 1.

The delay in switching the trigger 20 to the pulse time of the one-shot 16 serves to prevent false switching of said trigger during short-term signal drops at the second input of block 12, for example, during the intervals between words.

Switching the trigger 20 causes the first switch 4 to open and the second switch 5 to close. As a result, it appears at the first input of block 12, which causes the appearance of 1 at the output of the element OR 17 of the first circuit. In this case, the operation of the first circuit is completely identical with the operation of the second circuit.

Claims (2)

Claims 1. A four-wire telephone line interface with a two-wire differential system and a series-connected echo canceller and a threshold unit characterized in that. that, in order to increase the echo attenuation with an increased duration of the impulse transient response of the echo path. enter The first high-pass filter, the first key and the first adder, the second high-pass filter, the second key and the second adder are connected in series, and the first and second filters are low; frequency and control unit, the first and second outputs of which are connected to the control inputs of the first and second keys, respectively, the output of the differential system is connected to the combined inputs of the first high-pass filter and the first low-pass filter, the output of which is connected to the first input of the echo canceller, the second input of which is combined with the third input of the control unit and the second input of the second adder and connected to the output of the second low-pass filter, the input of which is combined with the input of the second high-pass filter, the output of the second key a first input connected to the control unit, the second input of which is combined with a second input of the first adder and the output connected to a threshold unit, a second adder connected to exit difsistemy entry. 2. The device according to claim 1, wherein the control unit contains two circuits, each of which contains a detector connected in series, a threshold unit, a delay unit, an OR element, an inverter and an AND element, as well as a one-shot, connected between the output of the threshold unit and the second input of the OR element, and the output of the OR element of the second circuit is connected to the second input of the AND element of the first circuit, the output of which is connected to the first the trigger setup input, to the second setup input of which the output of the element AND of the second circuit is connected, to the second input of which additional detector connected in series is connected and a threshold unit, the inputs of the detectors of the first and second circuits and the input of the additional detector are respectively the first, second and third inputs of the control unit, the first and second outputs of which are the direct and inverse outputs of the trigger. Srig.