JPH0334710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a voice switch circuit of a loudspeaker telephone device that enables high-quality telephone calls even under noisy conditions.

[Technical background of the invention]

Conventionally, as this type of circuit, there is a circuit as shown in FIG. 1, for example. This circuit is for microphone 1
A first transmission loss circuit 4 and a first reception loss circuit 5 are inserted in the transmission path from the line 2 to the speaker 3, and the reception path from the line 2 to the speaker 3, respectively. Then, the transmitting signal level on the input side of the transmitting speech loss circuit 4 and the receiving signal level on the output side of the receiving speech loss circuit 5 are respectively introduced into the audio switch control circuit 6 and compared, and the above-mentioned transmitting signal level is The loss amounts of the loss circuit 4 and the receiving loss circuit 5 are increased and decreased reciprocally. Further, a second speech loss circuit 7 is inserted between the microphone 1 and the first speech loss circuit 4 in the speech transmission path. Then, the noise detection circuit 8 receives the transmission signal output from the microphone 1.
The noise signal level is detected here, and the loss amount of the second transmission loss circuit 7 is adjusted in accordance with this noise signal level. In addition, in the figure, 9 and 10 are respective amplifiers for transmitting and receiving calls, and 11
indicate a hybrid circuit, respectively.

With this configuration, the level of the transmitting signal input to the audio switch control circuit 6 is lower than the level of the receiving signal when no transmission is being performed, so that the loss of the first transmitting loss circuit 4 is reduced. The amount of loss becomes large, and conversely, the loss amount of the reception loss circuit 5 becomes small, so that the circuit is in the reception state. On the other hand, if a voice of a predetermined level or higher is input from the microphone 1 in this state, the audio switch control circuit 6
The transmitting signal input level of the first
The amount of loss in the transmitting loss circuit 4 is small, and the loss amount in the receiving loss circuit 5 is small.
The amount of loss becomes large, and the circuit enters a transmitting state.

By the way, when used in a noisy place, the voice switch control circuit 6 is activated by this noise signal level and the circuit tries to shift to the transmitting state, but the noise level is not detected by the noise detection circuit 8. Since this is detected and the loss amount of the second transmission loss circuit 7 is adjusted in the direction of increasing, transition to the transmission state due to noise is prevented. Therefore, good call operation can be ensured even under noisy conditions.

[Problems with background technology]

However, in such a conventional circuit, when there is noise, the amount of loss in the second transmission loss circuit 7 increases, so when audio is input in this state, the audio signal level also decreases to the above-mentioned level. The loss is reduced by the attenuation effect of the transmission loss circuit 7 of No. 2. This makes it difficult for the audio switch control circuit 6 to detect the audio signal, and as a result, it becomes difficult for the circuit to shift to the transmitting state, making it more likely that words will be cut off.

Therefore, conventionally, the rate of increase in the amount of loss in the second transmission loss circuit 7 is reduced, thereby preventing problems such as audio interruptions. However, in this case, since the transmitting signal level generally increases, it becomes difficult for the audio switch control circuit 6 to detect the receiving signal level, resulting in a problem that it becomes difficult to perform a receiving interrupt.

[Purpose of the invention]

The present invention provides an audio switch circuit for a public address telephone device that is capable of smoothly and reliably transitioning to a receiving state without degrading call interrupt performance even under noisy conditions, thereby improving call quality. The purpose is to provide.

[Summary of the invention]

In order to achieve the above object, the present invention includes a hybrid circuit that sends and receives a transmitting signal and a receiving signal to a line system, and an output of a transmitting amplifier that amplifies the transmitting signal from a microphone. A receiving loss circuit interposed between a receiving path leading to the hybrid circuit and a receiving path leading a receiving signal derived from the hybrid circuit to a receiving amplifier, and an amount of loss in this receiving loss circuit. and a transmitting loss circuit whose loss amount is controlled reciprocally and which is connected in the transmitting path, the output of the transmitting amplifier which is the input side of the transmitting loss circuit and the receiving loss circuit. The amount of loss in the transmission loss circuit and the amount of loss in the reception loss circuit are reciprocally increased or decreased in response to the relative level difference of the reception signal from the transmission side, and the signal on the output side of the transmission amplifier is detected. By doing so, the reciprocal control of the amount of loss by the audio switch control circuit for the transmitting loss circuit and the receiving loss circuit is corrected in accordance with the noise.

[Embodiments of the invention]

FIG. 2 shows the configuration of an audio switch circuit according to an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals and will be explained.

A second reception loss circuit 20 is provided between the first reception loss circuit 5 and the amplifier 10 in the reception path. This circuit 20 is operated by a control signal from the noise detection circuit 8, and operates to reduce the amount of loss as the noise detection level increases.
The loss amount of the second reception loss circuit 20 and the loss amount of the first reception loss circuit 5 are set such that the sum thereof is equal to the loss amount of the reception loss circuit 5 of FIG. 1 in the absence of noise. It is stipulated in

Further, the voice switch control circuit 6 is introduced with a transmitting signal on the input side of the second transmitting loss circuit 7 of the transmitting path. The audio switch control circuit 6 is
The level of this transmitting signal and the second receiving loss circuit 20
The loss amount of the first transmission and reception loss circuits 4 and 5 is reciprocally increased or decreased according to the comparison result.

Because of this configuration, first of all, when there is almost no noise and the speaker is not transmitting, the loss in the first transmitting loss circuit 4 is large, and the loss in the first receiving loss circuit 5 is large. The amount is small and the circuit is now in a listening state. When the transmitted voice is input in this state, the high level transmitted voice signal before being attenuated by the second voice loss circuit 7 is input to the audio switch control circuit 6. Therefore, the level of this transmitting audio signal becomes higher than the receiving signal level, and as a result, the loss amounts of the first transmitting loss circuit 4 and the first receiving loss circuit 5 become small and large, respectively, which causes the circuit is in the transmitting state.

Now, when used in a place where the noise level is higher than a predetermined level, the voice switch control circuit 6 is operated by this noise, and the losses in the first transmitting and receiving loss circuits 4 and 5 are reduced to small and large, respectively. As a result, the circuit shifts to the transmitting state. However, the noise is detected by the noise detection circuit 8, and this circuit 8 adjusts the amount of loss in the second transmission loss circuit 7 so that the noise signal is detected by the noise detection circuit 8. 7 and is not sent to line 2. Further, when the noise is detected by the noise detection circuit 8 as described above, the second
The loss amount of the receiving loss circuit 20 is adjusted in the direction of decreasing. Therefore, when a reception signal arrives from the line 2 in this state, the loss that this reception signal receives in the first and second reception loss circuits 5 and 20 is small, so that the reception signal input to the audio switch control circuit 6 is The level becomes large to some extent, and as a result, the audio switch control circuit 6 makes the loss amounts of the first transmission and reception loss circuits 4 and 5 large and small, respectively. The circuit is therefore in a listening state.
In other words, even under noisy conditions, the call interruption is reliably performed.

In this way, with the voice switch circuit of this embodiment, the second reception loss circuit 20 is provided in the reception path to reduce the amount of loss in this circuit when noise occurs, so even when used in noisy conditions, However, it is possible to easily accept a reception interrupt, and as a result, it is possible to eliminate the problem of inability to hear the beginning of a word in the reception voice. Furthermore, since the transmitted voice is detected by extracting the signal from the input side of the second transmitting loss circuit 7 and guiding it to the voice switch control circuit 6, the noise level is reduced. Even if the loss amount of the second transmission loss circuit 7 is set to be large in order to reduce the loss, the transmission voice can be detected completely regardless of this loss amount.
Therefore, the problem of interruptions occurring at the end of the transmitted voice is resolved, and clear conversations can be made. Furthermore, the audio switch control circuit 6
As described above, the extraction of the transmitting signal level input to the transmitting signal is performed on the input side of the second transmitting loss circuit 7, so the loss amount of the second transmitting loss circuit 7 is set to be sufficiently large. This makes it possible to reliably prevent a problem such as a transmitting signal going around to a receiving channel via the hybrid circuit 11 and causing the audio switch control circuit 6 to malfunction due to the signal level, that is, blocking.

Note that the present invention is not limited to the above embodiment. For example, as shown in FIG. 3, each transmission loss circuit 4, 7 and each reception loss circuit 5, 20 used in FIG.
2, and the outputs of the noise detection circuit 8 and the audio switch control 6 are connected to the loss circuits 31 and 31, respectively.
The amount of loss may be controlled by supplying it to 32. In this way, it is sufficient to provide one loss circuit on the transmitting side and one on the receiving side, thereby simplifying the circuit configuration.

〔Effect of the invention〕

As described in detail above, the present invention includes a hybrid circuit that sends and receives transmitting signals and receiving signals to and from the line system, and a transmitting amplifier that amplifies the transmitting signal from the microphone. A transmission path leading to the circuit, a reception path leading the reception signal derived from the hybrid circuit to the reception amplifier, a reception loss circuit interposed in the reception path, and a loss amount of the reception loss circuit that is contradictory to the amount of loss of the reception loss circuit. a transmitting loss circuit whose loss amount is controlled and which is interposed and connected in the transmitting path, and from the output of the transmitting amplifier which is the input side of the transmitting loss circuit and the receiving loss circuit side. The amount of loss in the transmission loss circuit and the amount of loss in the reception loss circuit are reciprocally increased or decreased in response to the relative level difference of the reception signal of the receiver, and the signal on the output side of the front transmission amplifier is detected. Accordingly, the reciprocal control of the amount of loss for the transmitting loss circuit and the receiving loss circuit is corrected in accordance with the noise by the audio switch control circuit.

Therefore, according to the present invention, it is possible to reliably interrupt a call even in a noisy environment, and to smoothly and reliably transition from the receive state to the send state, thereby improving communication quality. It is possible to provide an improved audio switch circuit for a public address telephone device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional audio switch circuit, FIG. 2 is a block diagram of an audio switch circuit in an embodiment of the present invention, and FIG. 3 is a block diagram of an audio switch circuit in another embodiment of the invention. FIG. 1...Microphone, 2...Line, 3...Speaker, 4...First transmission loss circuit (TVL1), 5
...First receiving loss circuit (RVL1), 6...Audio switch control circuit, 7...Second transmitting loss circuit (TVL2), 8...Noise detection circuit, 9, 10...Amplifier, 11... ...Hybrid circuit, 20...Second
receiving loss circuit (RVL2), 31, 32... loss circuit.

Claims (1)

[Scope of Claims] 1. A hybrid circuit that sends and receives transmitting and receiving signals to and from the line system, and an output of a transmitting amplifier that amplifies the transmitting signal from the microphone to the hybrid circuit. a receiving path for directing the receiving signal derived from the hybrid circuit to the receiving amplifier; a receiving loss circuit interposed in the receiving path; A transmitting loss circuit whose transmission amount is controlled and which is connected interveningly in the transmitting path, and an output end side of the transmitting amplifier which is the input side of this transmitting loss circuit are connected to one input terminal and the other input terminal. A reception signal from the reception loss circuit side is input, and the amount of loss in the transmission loss circuit and the loss in the reception loss circuit are calculated in response to the relative level difference between the one input terminal side and the other input terminal side. an audio switch control circuit that reciprocally increases or decreases the transmission loss circuit and the reception loss circuit by detecting a signal on the output side of the transmission amplifier; A voice switch circuit for a public address telephone device, comprising a noise detection circuit for correcting the control of the amount of loss according to noise.