JP2774663B2 - Key telephone equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a key telephone device capable of making a conference call.

(Prior Art) The operation of a conventional key telephone apparatus when a conference call between two stations and one extension terminal is being conducted will be described with reference to FIG.

An audio signal input from the external terminal 10 to the main unit 10 through one of the office lines enters the time switch 2 through the codec 3 and is first sent to the bidirectional amplifying unit 25 and amplified there. Is returned to the conference call circuit 5. The conference call circuit 5 splits the input signal into two hands and sends it to the time switch 2. One of the split audio signals is transmitted to the other office line through the codec 4 and received by the external terminal 11, and the other audio signal is output. The signal is sent to the extension terminal 9 through the codec 8.

An audio signal input from the external terminal 11 through the other station line enters the time switch 2 through the codec 4 and
From here, it is first sent to the conference call circuit 5, divided into two hands, and sent to the time switch 2. One audio signal that has entered the time switch 2 is sent to the bidirectional amplifier unit 25 where it is amplified and returned to the time switch 2, where it is sent out through the codec 3 to one of the local lines and sent to the external terminal 10. The received voice signal is sent to the codec 8 and received by the extension terminal 9.

In this conference call, the two-way amplification unit 25 functions as a voice switch for preventing howling in the main device 1. That is, as shown in FIG. 5, the bidirectional amplifier 25 includes codecs 30 and 31, variable gain amplifiers 32 and 33, and a comparator 34, and converts the one-way input signal 26 to the amplifier 32.
And the input signal 29 in the other direction is amplified by the amplifier 33, and the level of the input signal 26 in one direction is compared with the level of the output signal 27 after amplification in the other direction. Are controlled so that a large gain is given to the low side and a small gain is given to the low side.

(Problems to be Solved by the Invention) In this conventional conference call, the external terminal 10 and the main unit 1
When the distance between the external terminal 11 and the main unit 1 is short and the line loss is small, the communication level with the external terminal 10 is amplified to an appropriate value by the bidirectional amplifier unit 25. Therefore, a conference call can be performed with a good voice level.

However, conversely, when the distance to the external terminal 10 is short and the distance to the external terminal 11 is long, the call signal with the external terminal 11 is not amplified because it does not pass through the bidirectional amplifier unit 25. As a result, an unbalanced state occurs in which the communication level with the external terminal 10 is high and the communication level with the external terminal 11 is low.

Accordingly, it is an object of the present invention to enable a conference call to be performed at a balanced call level even if the line loss of a plurality of office lines for performing a conference call is unbalanced.

[Configuration of the invention]

(Means for Solving the Problems) The present invention detects an input audio signal level from each office line performing a conference call in a key telephone apparatus capable of performing a conference call between a plurality of office lines and at least one extension terminal. Voice level detecting means, variable gain bi-directional amplifying means provided for each local line performing a conference call, and amplifying an input voice signal from each local line and an output voice signal to each local line; voice level detecting means And a gain control means for controlling the gain of each bidirectional amplifying means so as to correct the imbalance of the communication level caused by the line loss of each office line based on the detection result.

(Operation) In the key telephone apparatus of the present invention, during a conference call, the input audio signal level from each office line is detected, and a bidirectional amplification operation is performed on the input audio signal from each office line and the output audio signal to each office line. Is performed. At this time, based on the detection result of the input audio level from each office line, the communication level imbalance caused by the line loss of each office line should be corrected.
The gain of the bidirectional amplification operation for each station line is controlled.

(Example) Hereinafter, an example will be described.

FIG. 1 shows the configuration of an embodiment of the key telephone apparatus according to the present invention, and the same elements as those in FIG. 4 are denoted by the same reference numerals.

In the figure, a main device 100 includes a time switch 2 for performing digital exchange, codecs 3 and 4 for performing A / D / D / A conversion of audio signals between the office lines 10 and 11 and the time switch 2, and an extension terminal 9. A codec 8 for performing A / D / D / A conversion of an audio signal between the time switches 2 and a conference call circuit 5 for performing audio signal processing for a conference call are provided in the same manner as the main device 1 in FIG. Further, the main device 100 includes two bidirectional amplification units 6, 7, audio level detection circuits 20, 21 for detecting input audio signal levels from the office lines 10, 11, and audio level detection circuits 6, 7, respectively. Bidirectional amplification unit according to detection signal
A gain control unit 22 for controlling the gains 6 and 7 is provided.

The operation of the button telephone device when a conference call is established between the two office lines and one extension terminal is as follows.

An audio signal from one of the office lines 10 enters the time switch 2 through the codec 3 and is sent to one of the two-way amplifying units 6 where it is amplified. Is entered. The audio signal is split into two hands in the conference call circuit 5 and sent to the time switch 2. One of the split audio signals is sent to the other bidirectional amplifier unit 7 where it is amplified, and then the time switch is turned on again. 2 and transmitted to the other station line 11 via the codec 4. The other audio signal is sent from the time switch 2 to the extension terminal 9 via the codec 8.

Similarly, the voice signal from the other station line 11 enters the time switch 2 through the codec 4 and is sent to the two-way amplifier unit 7 from there, and is amplified again. Input to the circuit 5. This audio signal is also split into two hands by the conference call circuit 5 and sent to the time switch 2, and one of the split audio signals passes through the bidirectional amplifier unit 6, the time switch 2 and the codec 3 in that order to the office line 10. The other audio signal is sent from the time switch 2 to the extension terminal 9 via the codec 8.

The audio signal from the extension terminal 9 is input to the conference call circuit 5 through the codec 9 and the time switch 2, where it is split into two hands, and one of the audio signals is divided into the time switch 2, the two-way amplification unit 6, the time The signal is sent to the office line 10 via the switch 2 and the codec 3 in order, and the other audio signal is sent to the time switch 2, the bidirectional amplifier unit 7,
Station line via time switch 2 and codec 4 in order
Sent to 11.

The audio signal levels from the office lines 10 and 11 are
Each is detected by 21, and each detection signal is input to the gain control unit 22. The gain control unit 22 outputs gain control signals 23 and 24 for setting the communication levels of the office lines 10 and 11 to appropriate values to the bidirectional amplification units 6 and 7 based on the detection signals. Each of the bidirectional amplification units 6 and 7 has a portion that constitutes a voice switch for preventing howling, and a portion that adjusts the loop gain in accordance with the gain control signal from the gain control unit 22. The latter part operates according to the gain control signal to lower the gain if the input signal level from the office line is excessive, and to increase the gain if the input signal level from the office line is too low. Adjust to.

FIG. 2 shows a specific configuration of the level detection circuits 20, 21 and the gain control unit 22, and FIG. 3 shows a specific configuration of the bidirectional amplification unit 6 (or 7), respectively.

As shown in FIG. 2, the level detection circuits 20 and 21 include serial / parallel conversion circuits 37 and 38 for receiving serial PCM audio data input to the time switch 2 and converting the data into parallel data. Conversion circuits 37, 38
Code conversion circuit that converts PCM audio data output from a PC into a digital code with the number of bits suitable for gain control
It has 39,40. In addition, the gain control unit 22 has a gain stored in advance, the gain data representing various gain values.
ROMs 41 and 42 are provided. The gain ROMs 41 and 42 store the digital codes (detection signals) output from the level detection circuits 20 and 21.
Is received as an address, and specific gain data corresponding to the address is read out. The gain data read from these gain ROMs 41 and 42 are converted into analog signals by D / A converters 43 and 44, and are applied as gain control signals 23 and 24 to the corresponding bidirectional amplifier units 6 and 7, respectively.

Referring to FIG. 3, bidirectional amplification unit 6 (bidirectional amplification unit 7 also has the same configuration) includes codecs 30 and 31, variable gain amplifiers 32 and 33 having a constant variable gain, and variable gain amplifiers. A comparator 34 for controlling 32, 33,
Variable gain amplifiers 35 and 36 whose gains are controlled by the gain control signal 23. Variable gain amplifier 32,
33 and the comparator 34 constitute a voice switch, and control the gains of the amplifiers 32 and 33 reciprocally according to the magnitude relationship between the input audio level of the amplifier 32 and the output audio level of the amplifier 33, thereby reducing the loop gain to less than 1. To prevent howling. The variable gain amplifiers 35 and 36 adjust the loop gain in accordance with the gain control signal 23, thereby compensating for the line loss and securing an appropriate communication level.

As described above, the conference call between the two office lines and the extension terminal has been described as an example, but the present invention is not limited to this. Thus, the present invention can be applied to a case where the number of local lines or extensions is large.

〔The invention's effect〕

As described above, according to the present invention, a bidirectional amplifier for amplifying an input / output audio signal is provided for each station line during a conference call, and the gain of each amplifier is adjusted to the input audio level from each station line. Since the control is performed according to the situation, even if the line loss of each office line is unbalanced, it can be compensated and a balanced conference call can be realized.

Further, since the respective gains of the first and second amplifying units are reciprocally controlled, an optimum gain amount can be set within a range where the loop gain does not exceed a predetermined amount.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a state of a key telephone device according to an embodiment of the present invention during a conference call, and FIG. 2 is a circuit configuration of an audio level detection circuit and a gain control unit in the embodiment of FIG. FIG. 3 is a block diagram showing a circuit configuration of a bidirectional amplification unit in the embodiment of FIG. 1, and FIG. 4 is a block diagram showing a state of a conventional key telephone device during a conference call. FIG. 5 is a block diagram showing a circuit configuration of a bidirectional amplifying unit in the conventional device shown in FIG. 2 ... Time switch, 3,4,8 ... Codec, 5 ...
Conference call circuit, 6,7 ... bidirectional amplification unit, 9 ... extension terminal, 10,11 ... office line, 20, 21 ... audio level detection circuit, 22 ... gain control unit, 35, 36 ... Variable gain amplifier.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04Q 3/58 101 H04M 3/56 A H04Q 3/42 104

Claims (1)

(57) [Claims] 1. A key telephone apparatus capable of making a conference call between a plurality of office lines and at least one extension terminal, an audio level detecting means for detecting an input audio signal level from each office line for making a conference call, and a conference call. Variable gain bi-directional amplifier having a first amplifier for amplifying an input audio signal from each local line and a second amplifying unit for amplifying an output audio signal to each local line provided for each local line Means, for each of the bidirectional amplifying means, based on a detection result of the audio level detecting means, so that a loop gain in the apparatus does not exceed a predetermined amount. A key telephone device comprising: gain control means for reciprocally controlling a gain.