JPS6265526A - Transmission and reception equipment for two-wire line conference speech - Google Patents

Abstract

PURPOSE:To prevent the deterioration in S/N of a reception signal by providing a gain variable means switching the gain with a control signal representing either during transmission or reception while suppressing the gain change within a predetermined allowable range. CONSTITUTION:A control circuit 15 compares a transmission level with a reception level of a voice circuit 2 and when the former is higher, it is regarded to be during transmission, and when the latter is higher, it is regarded to be during reception, generates a signal representing either during transmission or reception and gives it to variable circuit 10-14 as a control signal thereby switching the gain of the circuits 10-14. The variable circuit 12 prevents the deterioration in the S/N in the reception signal during reception. The other circuits keep the gain of an echo path connected with an echo canceller 19 to a constant value either during transmission or reception and bring the width of each gain in the transmission and reception path switched during transmission and reception into a predetermined range.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a conference call transmitting/receiving device for a two-wire line.

[Conventional technology]

Conventionally, a device described in Japanese Patent Application No. 156,488/1988 has been proposed as a two-wire line conference call transmitter/receiver for carrying out calls between meeting rooms via a two-wire line with large transmission loss. ing. With this device, in order to improve the deterioration of the signal-to-sound ratio when receiving a received signal whose level has decreased slightly due to transmission loss in the two-wire line, an audio switch is placed immediately before the hybrid circuit connected to the line. The circuit is connected so that the applied input level of an analog-to-digital converter connected to the receiving path is varied in accordance with a relative level comparison value between the receiving path and the transmitting path.

[Problem that the invention seeks to solve]

However, in the conventional device described above, the gain of the transmitting path and the receiving path changes with the switching operation of the audio switch circuit. There is a problem with it sliding around.

It is an object of the present invention to solve the above-mentioned problems and prevent the deterioration of the signal-to-noise ratio of a received signal during reception while suppressing the gain change of the transmitting path and the receiving path within a predetermined tolerance range. An object of the present invention is to provide a conversation transmitting/receiving device for a wired line.

[Means for solving problems]

The device of the present invention is provided between a hybrid circuit connected to a two-wire line, a transmission path that guides a transmission signal emitted from a microphone to the hybrid circuit, and a reception path that guides a reception signal received by the hybrid circuit to a speaker. and an analog-to-digital converter connected to the receive path between the hybrid circuit and the echo canceller. In the wire-type communication communication transmitting and receiving device, the levels of the transmitting signal at a predetermined location on the transmitting path and the receiving signal at a predetermined location on the receiving path after cancellation of the echo signal are compared and the level is determined during transmitting. and a control means for generating a control signal indicating whether a call is being received, and a front lr! between the hybrid circuit and the analog-to-digital converter. one gain variable means connected to the receiving path and switching the gain in response to the control signal; and one gain variable means connected to at least one of the transmitting path and the receiving path after the analog-to-digital conversion and controlling the control signal sb. and at least one gain variable means for switching the gain in response to.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. A transmitter/receiver circuit 1 includes a transmission path that guides a transmission signal sent from a microphone 3 via an audio circuit 2 to a hybrid circuit 20, and a two-wire transmission path. and a reception path that guides a reception signal given from the line W of the formula via the hybrid circuit 2o to the audio circuit 2.

The audio circuit 2 performs amplification and analog-to-digital conversion of the transmitting signal generated by the microphone 3, digital-to-analog conversion and amplification of the received signal led from the transmitting/receiving circuit 1, and also performs the amplification and analog-to-digital conversion of the transmitting signal generated by the microphone 3. The echo signal generated by the audio feedback K from the microphone 3 to the microphone 3 is erased. A digital transmission signal line sent by the audio circuit 2, a variable circuit 10, a digital-to-analog converter (D/A) 16, and a transmission path that leads the variable circuit 11 to the hybrid 20, and a control circuit 1. Sent to 15th. The transmit signal passing through the transmit path is converted into an analog signal at the D/person 16. The analog transmitter signal is sent to the line W via the hybrid circuit 20. On the other hand, the analog reception signal received from the line W passes through the hybrid circuit 20 and then passes through the variable circuit 12.
, analog-digital converter (A/D) 17, variable circuit 13, echo canceller? (EC) 19, variable circuit 14
, and amplifier 18 to the receiving path leading to the audio circuit 2. The signal sent out by the receiving path is sent to the system beaker 4 through the audio circuit 2 for audio reproduction, and is also sent to the control circuit 15. In addition to the receiving signal, the receiving path includes
As shown by the broken line arrow B, an echo signal generated by the transmission signal loop in the hybrid circuit 20 is sent.

EC19 is provided to eliminate this echo signal. The signal passing through the receiving path is converted into a digital signal by the A/D 17.

The control circuit 15 compares the transmission level and the reception level of the audio circuit 2, and if the former is higher, it considers that the call is in progress, and if the latter is higher, it is assumed that the call is in progress, A signal indicating whether a call is being sent or received is generated and sent to the variable circuits 10 to 14 as a control signal. Each of the variable circuits 10 to 14 switches the gain depending on whether a control signal given from the control circuit 15 indicates that a call is being sent or a call is being received. Of the variable circuits 10 to 14, the variable circuit 12 is provided to prevent deterioration of the signal-to-noise ratio of the reception signal during reception, and the others are used to adjust the gain of the echo path connected to the EC 19 during transmission and reception. Both of them are kept at a constant value, and the gain of each of the transmitting and receiving paths is set so that the switching range between transmitting and receiving is within a predetermined range.

That is, first, assuming that the gain of the variable circuit 12 during transmission is 0 decibels (dB), the input full-scale voltage of the A/D 17 will be higher than the level at which the echo signal of the transmission signal reaches the A/D 17. It is difficult to set it up. On the other hand, the reception signal that arrives at the variable circuit 12 while receiving a call is at a much lower level than the input full-scale voltage of the A/D 17, so if it is sent directly to the A/D 17 and converted into a digital signal, it will be converted into a signal pair (quantized). The noise ratio deteriorates considerably. In order to prevent this signal-to-noise ratio deterioration, the gain of the variable circuit 12 during reception is adjusted to
It is set sufficiently large so that the level arriving at D17 does not exceed the input full-scale voltage. In this way, each gain of variable circuits 11 and 13 is adjusted during transmitting and listening so that the sum of the gains of variable circuits 11 to 13 remains constant even if the gain of variable circuit 12 is switched between transmitting and receiving. Select.

Further, each gain of the variable circuit 10 and the variable circuit 14 during transmitting and receiving is selected so that the switching range of each gain of the transmitting path and receiving path during transmitting and receiving is a predetermined value. It is.

Therefore, in this embodiment, the gain changes of the transmitting path and the receiving path are suppressed within a predetermined allowable range, and the signal-to-noise ratio deterioration of the received signal during reception is suppressed without causing large fluctuations in the playback volume as in the conventional case. can be prevented.

Figure 2 +1) and (b) show the variable circuit 10 in this embodiment.
FIG. 14 is a block diagram illustrating an example of the configuration of components 1 to 14; Same figure +a
), the input signal is guided to one switching terminal of the switch 8W, and is also guided to the other switching terminal through the amplifier 21. 'Switch S world daughter, control circuit 15
The connection is switched in response to a control signal sent from the device, and OdB is maintained during a call.

Also, while receiving a call, the gain is switched to positive. The variable circuit in the figure (bl) is an attenuator 22 in place of the amplifier 21 in the figure (a).
is connected, and the gain switches to OdB while transmitting and to negative gain while receiving.

FIG. 3 is a block diagram showing another example of the configuration of the transmitting/receiving circuit 1. As shown in FIG. Variable circuit 10 or 1 in the embodiment shown in FIG.
4 is not necessarily all necessary, except for the variable circuit 12 which is necessary to prevent signal-to-noise ratio deterioration during reception, and how to set each gain of the transmission path and reception path during transmission and reception. In some cases, it may be possible to partially remove it. FIG. 3 shows an example of this, and is a configuration example in which the gains of the transmitting path and the receiving path are maintained at constant values even when switching between transmitting and receiving is performed. In this case, variable circuits 10, 11 and 14 in FIG. 1 can be removed, the circuit in FIG. 2(a) is used for variable circuit 12, and the circuit in FIG. 2(b) is used for variable circuit 13. may be used so that the sum of the gains of the variable circuits 12 and 13 becomes O dB both during transmitting and during receiving.

〔Effect of the invention〕

As explained above, the present invention provides a two-wire line conference call capable of preventing deterioration of the signal-to-noise ratio of the received signal during reception while suppressing the gain change of the transmission path and the reception path within a predetermined allowable range. This has the effect of realizing a transmitting/receiving device.

[Brief explanation of drawings]

FIG. 1, FIGS. 2(a) and (b), and FIG. 3 are block diagrams each showing an embodiment of the present invention. 1...Transmission/reception circuit, 2...Audio circuit,
3...Microphone, 4...Speaker, 10-14...Variable circuit, 15...
Control circuit, 16... group, digital-to-analog converter (
D/A), 17... group analog-digital converter (
A/D), 18, 21...Amplifier, 19...
...Echo canceller (EC), 20. Old... Hybrid circuit, 22... Attenuator, SW...
・Switch O

Claims (1)

[Claims] A hybrid circuit connected to a two-wire line, a transmission path that guides a transmission signal emitted from a microphone to the hybrid circuit, and a reception path that guides a reception signal received by the hybrid circuit to a speaker. A two-wire line conference call having a transmitting and receiving circuit including an echo canceller for canceling echo signals generated in a hybrid circuit and an analog-to-digital converter connected to the receive path between the hybrid circuit and the echo canceller. In the transmitting/receiving device, the levels of the transmitting signal at a predetermined location on the transmitting path and the receiving signal at a predetermined location on the receiving path after cancellation of the echo signal are compared to determine whether the transmitter is transmitting or receiving a call. control means for generating a control signal indicative of the control signal; one gain variable means connected to the receiving path between the hybrid circuit and the analog-to-digital converter for switching the gain in response to the control signal; and at least one gain variable means connected to at least one of the transmitting path and the receiving path after the analog-to-digital conversion and switching the gain in response to the control signal. Conference call transmitting/receiving device for telephone lines.