JPS61214850A - Anti-sidetone circuit for telephone set - Google Patents

Abstract

PURPOSE:To keep always a good sidetone state by providing a side tone component detecting circuit of a pilot signal and comparing the detection output of this circuit with a preliminarily set reference value to select and connect automatically a balance circuit of good sidetone state. CONSTITUTION:One balance circuit 8 is selected in an anti-sidetone circuit 9 from several prepared balance circuits of a balance circuit group 10 by a selecting circuit 11. Selection of the circuit 11 is controlled by a computer CPU 12. The pilot signal is detected from the sidetone signal outputted from the circuit 9 by a pilot component detecting circuit 13 consisting of a BPF and is taken into the CPU 12 through an A/D converter 14. The CPU 12 compares this signal level S1 with a preliminarily set level L; and if the level S1 is equal to or lower than the level L, the good sidetone state is discriminated, and switching of the balance circuit by the circuit 11 is not performed. If the level S1 is higher than the level L, the bad sidetone state is discriminated to switch the balance circuit.

Description

[Detailed Description of the Invention] B) Industrial Application Field The present invention connects a base unit connected to a telephone line and a handset having a handset by wireless communication, The present invention relates to a cordless telephone that makes a call to a destination telephone, and provides a control circuit for reducing the volume that is returned to the handset as sidetone when transmitting a call.

(b) Conventional technology.

Conventionally, in this cordless telephone, as shown in FIG. ) and a portable handset, i.e., handset (3), and the desired call destination is connected to the telephone line by the transmitter (4) and handset (5) of the handset (3). By carrying the handset (3) with you, you can make cordless calls from any desired location.

Now, generally speaking, like a telephone, there are four parts: a transmitting system and a receiving system.
When a line system and a two-line system subscriber line of a telephone line are coupled, there is a phenomenon (this phenomenon is called sidetone) in which the transmitted signal is reflected at the coupling point and returns to the receiver (5) of the speaker. If this side volume (7) is too high, it will interfere with telephone calls, so in order to reduce the side volume, a transformer and balance circuit as shown in Figure 6'17II2 (
A side sound prevention circuit (9) composed of 8) is used as a coupling stage.

In order to reduce the side volume in this side sound prevention circuit, it is required that the balance circuit (8) in Figure 1 has impedance matching with the telephone line (2) (subscriber line and its terminal load). (The state of matching is called sidetone balance.)

However, the impedance of a telephone line is 0, but it also varies depending on the wire diameter and distance of the subscriber's line, for example.

It is difficult to achieve sidetone balance for all line conditions.1 Usually, a balanced circuit is designed to achieve sidetone balance for specific line conditions (1), for example, wire diameter 0.5 tone, line summary 3- A method of setting impedance is used. Therefore, in the above method, the side sound characteristics may deteriorate considerably depending on the line conditions, and a side sound prevention circuit that exhibits good side sound characteristics regardless of the line conditions is desired.

Now, as mentioned above, sidetone balance can be achieved by impedance matching between the telephone line (2) and the balance circuit (8), so as a countermeasure for sidetone, several types of balance circuits are provided, depending on each line condition. One possible method is to select all suitable ones. In this case, if the main body and handset are combined, such as a general standard telephone, the main body is equipped with a balance circuit changeover switch, which can be easily switched during a call to select the optimum state. On the other hand, a feature of cordless phones is that they can be used to make calls using the handset at a location far from the base unit (the side sound protection circuit is built into the base unit), and therefore the switch described above can be easily changed. do not have.

(c) Problems to be Solved by the Invention In view of the above points, the present invention provides a method of controlling a cordless telephone so that it always has a good sidetone state under various line conditions.

轡Means for Solving the Problems The sidetone countermeasure of the present invention uses several types of balanced circuits (8) as described above.
) is the same as the conventional one, but the basic feature is to automatically search for a more suitable balanced circuit.

This point will be explained below.

In cordless telephones, in order to open and close the connection to the telephone line (an operation equivalent to a 7-touch switch on a regular telephone), the handset side (3) superimposes a pilot signal on the back door signal and sends it for control. method is used. While the main unit is receiving this pilot signal, the relay αgJiO
N control to activate the connection to the telephone line (ENABLE).
), and if the pilot signal is not received, the connection is set to DISABLE. In order to reduce the deterioration in sound quality caused by the pilot signal that is superimposed on the audio signal and transmitted, the audio frequency (500A to 3.5KH) is generally
A signal having a higher frequency (1, for example, about 5 KHz) than the pilot signal is used as a pilot signal. The sidetone component of this pilot signal is at a constant level during a call. The present invention focuses on this point and attempts to improve sidetone characteristics by detecting the level at which this pilot signal returns as sidetone and searching for a state in which this level becomes low.

(E) Function In the present invention, the balance circuits provided in advance are automatically switched one after another, the pilot signal frequency component in the sidetone signal is detected each time, and the frequency component of the pilot signal in the sidetone signal is automatically switched until this level becomes equal to or less than a preset value. The balance circuit is switched to search for conditions with good sidetone conditions.

With this operation, it is possible to automatically control to always maintain a good sidetone condition even under any telephone line line conditions.

(f) Example Next, the sidetone characteristics will be explained with reference to FIG.

In FIG. 3, (a) shows the characteristics when the sidetone is balanced, and (to) shows the characteristics when the sidetone is poor.

Here, the frequency band of the pilot signal (5KHz in the figure)
Focusing on the level of , it can be seen that it is possible to judge whether the sidetone condition is good or bad based on the magnitude of this level. As mentioned above, the sidetone component of this pilot signal is at a constant level during a call. The present invention focuses on this point and attempts to improve sidetone characteristics by detecting the level at which this pilot signal returns as sidetone and searching for a state in which this level becomes low.

next'! FIG. llI4 shows an embodiment of the present invention. The balance circuit (8) in the side sound protection circuit (9) is selected from the balance circuit group (1 (I) by the selection circuit συ. The selection control by this selection circuit σD is performed by the microcomputer 0PU (121 This is done by the side sound protection circuit (9
) From the output sidetone signal, a pilot signal frequency component signal (P in Figure 3) is detected by a pilot signal component detection circuit [3, such as a bandpass filter].
The detected signal is converted to A by A/D conversion circuit a4.
/ After D conversion, it is loaded into the microcomputer (17J).

The basic operation of this circuit will be explained below. first.

Assume that the balance circuit (Hl) (a-, , ) is selected as the initial value. At this time, the pilot signal component in the sidetone signal in this balance circuit is taken into the microcomputer α2. This signal level (this is set as 81) is compared with a preset level (this is set as L), and if 81≦, it is determined that the sidetone condition is good, and the 1 selection circuit (1)) is used to balance the signal level. Set to state 1) of Hl without switching the circuit (i.e., maintain state)
. If it is 5z)L, it is determined that the sidetone condition is poor and the balance circuit is switched. In the balanced circuit (8-2) after switching (this is referred to as Hl), detect the sidetone level (pilot frequency band) 82 in the same way as above, compare it with t-L, and find that 82≦L・According to the result of 82>L, the balance circuit is maintained or switched. By repeating this operation, a balanced circuit state, f, in which the sidetone state generally becomes good (sidetone level≦reference value L).

You can issue a heading and keep it in this state.

However, with the equipped balancing circuit group (1G), there may be cases where the sidetone level is not as good as the reference value. Examples of countermeasures in this case are shown below. We will explain how to set the balanced circuit to minimize the sound level.To set this state, proceed as follows.First, in the balanced circuit (Hl) state, set 8°1 as described above. The position information corresponding to Hl and the level value information of 81 are stored in lRAMσ9.Next, in the case of 81>L, the balance circuit is switched to H2, so in the state of Hl at this time, Sidetone level value 52
Compare the size with t-L. Also, compare the value of Sl stored in RAM (15) with 82 (1781≧82, then update the position information stored in RAM to Hl (H1 → H2) 6 (II) 81 < 8
If it is 2, the position information stored in the RAM is set to it (in this case, the information corresponding to Hl remains stored).

Next, when 82) is L, the balance circuit (8) switches to H5, and at this time as well, the operation of comparing the magnitude and storing in the RAM is repeated.

If you perform the above operations.

(a) If there is a balanced circuit (8) in which the sidetone level is below the reference value, that balanced circuit state is maintained.

(b) If a balanced circuit with which the sidetone level is below the reference value cannot be found, then in the state of the balanced circuit that was last selected, the position information of the balanced circuit with the minimum sidetone level is stored in RAMα9. ing.

Therefore, the balanced circuit state is switched to correspond to the information stored in this RAM. As a result, a group of balanced circuits (
The best sidetone condition in 1) can be maintained. Note that αe is a transformer, and αη and η are boats.

By carrying out the above operation, it is possible to automatically select the optimum balanced circuit t for any line condition. Note that the operation of searching for the optimal balanced circuit is performed over a telephone line (
You can go only to the start point connected to 2), or
Further, the operation may be repeated at regular intervals.

(G) Effects of the Invention As described above, according to the present invention, it is possible to automatically set the best antiperspirant level at all times, so it is possible to prevent the adverse effect of antiperspirant on phone calls, and to enjoy comfortable phone calls. The present invention is very effective in practice.

[Brief explanation of drawings]

′! Figure J1 is a block diagram of a cordless telephone, Figure 2 is a circuit diagram showing its side sound prevention circuit, Figure 3 is an example of frequency characteristics of side sound, and Figure 4 is an embodiment of the side sound prevention circuit of the present invention. FIG. 2 is a block circuit diagram. (1)...Base unit of cordless telephone, (2)...Telephone line. (3)... Handset of cordless telephone, (9)... Side sound protection circuit, (8)... Balance circuit in side sound protection circuit, (1
[...balanced circuit group, ari...0PU (microcomputer), a3...detection circuit, α9...RAM,
(G)... Sidetone component of the pilot signal.

Claims (2)

[Claims] (1) Has a base unit and transmitter/receiver connected to a telephone line,
In a cordless telephone equipped with a handset that performs wireless communication with the base unit and makes a call to a called party via the telephone line, (a) a transmit signal from the handset of the handset is transmitted; (b) a side sound prevention circuit comprising a plurality of balanced circuits that can be selectively connected in order to reduce side sounds returning to the handset of the handset; and (b) a transmission signal for opening/closing connection from the handset side to a telephone line. (c) Compare the detection output of the detection circuit with a preset reference value, and if the detection output is less than the reference value; A side sound prevention circuit for a telephone, characterized in that a control circuit for controlling selection so as to maintain the selected balanced circuit is provided on the base unit side, and a balanced circuit with a good side tone condition is automatically selected and connected. . (2) The control circuit compares the detection output of the detection circuit with a reference value. If the detected output exceeds the reference value, switch to another balanced circuit, compare the sidetone component detected outputs between the balanced circuits, and perform switching control so that the balanced circuit with the minimum detected output is selected and connected. A side sound protection circuit for a telephone according to claim 1.