JPH0218617Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a telephone communication device, which realizes a more natural telephone conversation by switching to the receiving state when the caller stops transmitting, even when the receiving signal is small. The purpose is to

Conventional telephone equipment uses a variable loss circuit that can adjust the amplification level for the transmitting system and the receiving system, and compares the transmitting level and the receiving level. A control circuit controls the amplification degree of the variable loss circuit according to the output compared with the value obtained by applying a receive signal to the control circuit via the variable loss circuit when transmitting or receiving a call. This communication device is equipped with a switching means that selects whether to apply the signal directly without passing it through the loss circuit, and it is variable whether the input of the receiving system that is applied to the AC compression circuit is obtained directly from the hybrid transformer depending on when transmitting or receiving a call. At the same time, the receiving system signal obtained from this selection is compared with the transmitting system signal to control the amount of loss in the variable loss circuit provided in the transmitting system and the receiving system. ing.

However, in this case, if there is noise on the transmitting side and the received signal is small, the received signal from the hybrid transformer in the transmitting state will be greatly influenced by the sidetone of the transmitted signal, and the received signal will be buried in the sidetone. There are disadvantages in call quality, such as not being able to make a call without switching to receiving, or the beginning of a conversation often being cut off.

The present invention eliminates these drawbacks. An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a block diagram of a hands-free communication device which is an embodiment of the present invention, and FIG. 2 is a timing chart of the outputs of each part of the device.
In the figure, 1 is a microphone, 2 is a speaker, 3, 4, 5, 6
is an amplifier, 7 and 8 are variable loss circuits, 9 is a hybrid transformer, 10 is a transmitting signal input circuit, 11 is a receiving signal input circuit, 12 is a differential amplifier, 13, 1
4 is a comparator that compares the output of the differential amplifier 12 with the set values S ₁ and S ₂ respectively; 15 is a variable loss circuit 7;
Flip-flops 16 and 17 are switches that are turned on and off in accordance with the output of flip-flop 15. 18 is switch 181, 182
19 is a time limit circuit, 2
0 is a DC bias circuit consisting of a resistor and a bias power source.

Next, its operation will be explained.

Here, when the receive priority switch 18 is switched as shown in FIG. 1, the direct current bias circuit 20 is connected to the receive input circuit 11 by the switch 182 during transmitting, so there is no output from the amplifier 6. Since a constant bias D is applied to the receiving input circuit 11, the output of the transmitting input circuit 10 is R _T and the receiving input circuit 11 is
If the output of is R _R and the set value S ₂ is -T, then
When the transmitted voice becomes low and R _T /R _R <-T, that is, R _T /D <-T, the output of the comparator 13 becomes "H" and the state is switched to the receiving state. At this time,
The switch 181 causes the timer circuit 19 to switch to the comparator 14.
and the flip-flop 15, and the timer circuit 19 sends out a transmission switching signal and sets the timer.
Only T _D will be forcibly retained.

Figure 2 A is the output of comparator 14, and B is the output of comparator 1.
3, C shows the input to the set terminal S of the flip-flop 15 when the receive priority switch 18 is in the opposite state to that in FIG. 1, and D shows the output from the same output terminal Q. The same house is Switch 18
is in the state shown in FIG. 1, and shows the input to the set terminal S of the flip-flop when the time limit circuit 19 is inserted, and the same shows the output from the output terminal Q. time
T _D is the operation delay time, and T _D1 is the transmission holding time.

Furthermore, by providing the timer circuit 19 in this manner, the switching from transmitting to receiving can be delayed by a certain period of time T _D , thereby preventing unpleasant end-of-word interruptions during a telephone call.

As is clear from the above explanation, the present invention applies the received signal directly to the input side of the control circuit during the transmitting state without going through the variable loss circuit, and also applies a predetermined bias at this time. However, when in a receiving state, the receiving signal is applied to the input side of the control circuit via the variable loss circuit, and the predetermined bias is not applied.
Therefore, in the transmitting state, if a receiving signal is input even if it is small, the bias can easily switch to the receiving state, and in the receiving state, even if the transmitting signal is relatively small, it is easy to switch to the transmitting state. It has the advantage that it can be interrupted.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a hands-free communication device according to an embodiment of the present invention, and FIG. 2 is a timing chart of the same. 1...Microphone, 2...Speaker, 3, 4, 5,
6...Amplifier, 15...Flip-flop, 1
6, 17... switch, 18... call priority switch, 19... time limit circuit, 20... direct current bias circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) Comparing the transmitting level and the receiving level with variable loss circuits that can adjust the amplification degree provided in the transmitting system and the receiving system, respectively, and further comparing the comparative output and the transmitting level. a control circuit that controls the amplification degree of the variable loss circuit according to the output compared with a predetermined value when receiving a call and a predetermined value when receiving a call; switching means for applying a reception signal to the control circuit via the variable loss circuit when receiving a call;
A telephone communication device comprising: a DC bias circuit that applies a constant bias to the reception signal input side of the control circuit during transmission, and switches to the reception state when the transmission signal disappears even if the reception signal is small. (2) The communication device according to claim 1 of the utility model registration claim, wherein the direct current bias circuit can be added freely by a receive priority switch.