JPH0548987B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a transmitting switching circuit used in telephones, etc., and particularly relates to a DTMF (DualTone Modulated
This relates to switching between a dial signal consisting of a frequency (frequency) signal and a transmitting signal.

[Conventional technology]

FIG. 2 shows the configuration of a telephone device that automatically switches calls using a handset placed on a desk, for example.

In this telephone device, the signal transmitting/receiving circuit 2 is generally called a speech network, and is installed at the signal input/output section of the telephone device to send dial signals or outgoing signals from the telephone device to the telephone line 4. Alternatively, it is used to receive a calling signal or a receiving signal from an exchange. Therefore, when the telephone number of the other party is entered from a dial (not shown), a dial signal output in response to the dial operation from the dial signal sending circuit 6 as a dial signal source is transmitted through the amplifier 10 of the transmitting system 8 and sent as a signal. The signal is added to the signal transmitting/receiving circuit 2, and is transmitted from the signal transmitting/receiving circuit 2 to the telephone line 4. In this case, a push button type dial is used and the dial signal sending circuit 6
In the case of the DTMF method, a DTMF signal is sent out in response to dial input.

In this telephone device, the handset 12
The microphone 14 is installed in a housing installed on a tabletop.
and a speaker 16 are installed integrally, and the audio signal generated in the microphone 14 by the audio input is added to the transmission line 8, and then passes through the amplifier 18, the call switching circuit 20, and the amplifier 10. , is sent from the signal transmitting/receiving circuit 2 to the telephone line 4. On the other hand, the receiving signal received by the signal transmitting/receiving circuit 2 from the telephone line 4 is transmitted to the receiving system 22.
The received voice is reproduced from the speaker 16 via the amplifier 24, the call switching circuit 20, and the amplifier 26.

The call switching circuit 20 switches between sending and receiving calls by comparing the signal levels of the sending signal and the receiving signal, and the comparator 28 compares the levels of the sending signal and the receiving signal. When the level of the transmitted signal is higher than that of the received signal, a comparison output is generated according to that level, and when the level of the received signal is higher than that of the transmitted signal, a comparison output is generated according to that level. do. In response to this comparison output, the switching control circuit 30 generates a switching control current, and a current control amplifier ( CCA) 32,
34 amplification gain is controlled. Therefore, if the transmitting signal level exceeds the receiving signal level,
Since the CCA 32 is in the signal passing state and the CCA 34 is in the signal blocking state, and when the receiving signal level exceeds the transmitting signal level, the CCA 34 is in the signal passing state and the CCA 32 is in the signal blocking state.
Switching between transmitting and receiving calls is performed.

[Problem that the invention seeks to solve]

In such a telephone device, the conventional signal transmitting/receiving circuit 2 has terminals 36, 38 as shown in FIG.
An equivalent resistance 42 equal to the resistance 40 of the telephone line 4 is connected in series with the telephone line 4 between the lines, and a dial signal (DTMF) and a voice signal are sent through the equivalent resistance 42. The reception signal from the telephone line 4 is configured to be received from the telephone line 4 via a comparison amplifier 44.

This signal transmitting/receiving circuit 2 includes an amplifier 10.
Install voltage dividing resistors 46 and 48 that divide the output of
In the transmitting mode, the signal voltage obtained by the transmitting signal at the voltage dividing point of the voltage dividing resistors 46 and 48 is made equal to the signal voltage appearing at the resistor 40, and the transmitting signal is not output to the comparator amplifier 44. It is set as follows.

In this case, in order to prevent dial tone from being generated from the receiving line 22 during dial operation, the dialing signal is treated in the same way as the sending signal and is sent to the telephone line 4 via the equivalent resistance 42. The transmission level of the dial signal sent to the dial signal causes a loss of about 6 dB due to the equivalent resistance 42.

By the way, in public telephone lines, the transmission level of dial signals is standardized. For example, when the voltage from the telephone line is low due to long distances, it is necessary to maintain the transmission level required by the standard. I can't.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a transmission switching circuit which prevents dial signal attenuation and maintains a necessary transmission level with a simple configuration.

[Means for solving problems]

As illustrated in FIG. 1, the transmitting switching circuit of the present invention connects an equivalent resistor 42 having a resistance value equivalent to that of the telephone line 4 in series to the telephone line, and transmits the transmitting signal through the equivalent resistor. At the same time, voltage dividing resistors 46 and 48 are connected in parallel to the equivalent resistor and the series circuit of the equivalent resistors, and the receiving signal is transmitted from the telephone line with the voltage dividing point of the voltage dividing resistor as a reference potential. a transmitting/receiving circuit 2 equipped with a comparator amplifier 44 installed at the transmitting/receiving end thereof, the transmitting/receiving signal output circuit transmitting the transmitting signal to the telephone line via the equivalent resistance; (amplifier 52); a dial signal output circuit (amplifier 50) that receives a dial signal from a dial signal generation source (dial signal transmission circuit 6) and directly sends it to the telephone line; dial signal detection means (signal level detection circuit 56) which detects the presence or absence of the dial signal based on the output of the dial signal detection means; The present invention is characterized in that it includes output switching means (operation switching circuit 54) for switching the transmitting signal output circuit to an operating state at times other than when dialing signals are being sent.

[Effect]

The outgoing call switching circuit of the present invention operates from a dial signal generation source (dial signal sending circuit 6) to a dial signal output circuit (amplifier 52) that sends out a outgoing call signal to the telephone line via an equivalent resistance. A dial signal output circuit (amplifier 50) is installed to receive the signal and send it directly to the telephone line. By providing a separate output circuit and sending the dial signal directly to the telephone line without going through an equivalent resistance, it is possible to suppress a drop in the level of the dial signal.

Then, a dial signal detection means (signal level detection circuit 56) is installed to receive the output of the dial signal generation source and detect the presence or absence of a dial signal, and an output switching means (operation switching circuit 54) is installed to detect the dial signal. Depending on the detection output of the means, the dial signal output circuit is switched to an operating state when a dial signal is being sent out, and the transmitting signal output circuit is switched to an operating state when not transmitting a dial signal, and transmission of the dial signal and transmitting signal are performed separately. By doing so, interference between the two transmissions is prevented.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a transmission switching circuit according to the present invention.

As shown in FIG. 1, the transmitting switching circuit is installed on the input side of the transmitting signal and dialing signal of the conventional signal transmitting/receiving circuit 2, and is connected to the dialing signal transmitting circuit 6 of the telephone device shown in FIG. The dialing signal (DTMF) is directly sent to the telephone line 4 via an amplifier 50 installed as a dialing signal output circuit separately from the transmitting signal output circuit, and the transmitting signal from the transmitting line 8 is , after passing through an amplifier 52 installed as a transmitting signal output circuit, the telephone line 4 is connected to the telephone line 4 via an equivalent resistance 42 equal to the resistance 40 of the telephone line 4.
sent to.

A driving voltage V _CC is selectively applied to the amplifiers 50 and 52 via an operation switching circuit 54 installed as an output switching means that switches the output according to the detection output from the dial signal detection means. In this example, the operation is switched by selectively applying the drive voltage V _CC , and either one of the amplifiers 50 and 52 is controlled to be in a signal passing state or a signal blocking state.

A signal level detection circuit 56 and a level comparator 58 as dial signal detection means are installed before the amplifier 50. The signal level detection circuit 56 connects the dial signal to a diode 60.
The detection output is sent to the capacitor 62.
to obtain a DC output according to the dial signal. This DC output is applied to a level comparator 58 and compared with a reference dial signal level, and if there is a dial signal to be detected, the level comparator 58 generates an H (high potential) output. This output is applied to the operation switching circuit 54 as an operation switching signal.

Therefore, when there is a dial signal, the operation switching circuit 54 is closed to the equivalent contact a side by the output of the level comparator 58, and the drive voltage is applied to the amplifier 50.
V _CC is applied, and only amplifier 50 is controlled to pass the signal. In this case, the dial signal passed through the amplifier 50 is sent directly to the telephone line 4 from the terminal 38.

In addition, when there is no dial signal, the operation switching circuit 54 is closed to the equivalent contact b side by the output of the level comparator 58, and the driving voltage V _CC is applied to the amplifier 52, so that only the amplifier 52 is in the signal passing state. controlled. The transmission signal that has passed through the amplifier 52 is sent from the terminal 36 to the telephone line 4 via the equivalent resistor 42.

In this case, the resistance values of resistors 40 and 42 are R _L ,
R _L ′ (R _L ≒ R _L ′), the resistance values of resistors 46 and 48 are R ₁ ,
R ₂ , the transmission signal voltage V _p output from the amplifier 52,
If the voltage due to the transmission signal generated at the terminal 38 is V _OL , then the voltage V _OL is V _OL = V _O · R _L / (R _L + R _L ′) ...(1), and at this time, the resistance The divided voltage generated by the transmitting signal at the voltage dividing points 46 and 48 is V _OL ′
Then, this voltage V _OL ′ becomes V _OL ′=V _O ·R ₂ /(R ₁ +R ₂ ) ……(2). Therefore, in this case the comparator amplifier 44
_{The output V OR generated at _ _ _ _ _} If the relationship between the values R _L , R _L ′, R ₁ , and R ₂ is R _L ′/R ₁ =R _L /R ₂ (4), then in the transmitting mode, the output of the comparator amplifier 44
V _OR becomes zero, and no leakage of the transmitting signal occurs.

Further, in the receiving mode, since the terminal 36 is grounded, the receiving signal from the telephone line 4 can be taken out from the terminal 38 via the comparator amplifier 44.

〔Effect of the invention〕

As explained above, according to the present invention, the transmission of the dial signal or the transmitting signal is switched depending on the presence or absence of the dialing signal, and the dialing signal is transmitted to the telephone without going through a resistance for passing the transmitting signal. Since it is sent directly to the line, it is possible to prevent loss of the sending level of the dial signal, and even at low voltage, it is possible to obtain a sending level twice as high as the conventional sending level.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the transmitting/receiving circuit of the present invention, FIG. 2 is a block diagram showing the configuration of a telephone device, and FIG. 3 is a circuit diagram showing a conventional signal transmitting/receiving circuit. 2...Signal transmission/reception circuit, 4...Telephone line, 6...
Dial signal sending circuit (dial signal generation source),
42...Equivalent resistance, 44...Comparison amplifier, 46,
48... Voltage dividing resistor, 50... Amplifier (dial signal output circuit), 52... Amplifier (sending signal output circuit), 54... Operation switching circuit (output switching means), 5
6...Signal level detection circuit (dial signal detection means).

Claims (1)

[Claims] 1. An equivalent resistor having a resistance value equivalent to that of a telephone line is connected in series to the telephone line, and a transmission signal is sent to the telephone line via the equivalent resistor,
A signal transmitting/receiving circuit is provided, in which a voltage dividing resistor is connected in parallel to the equivalent resistor and the series circuit of the equivalent resistor, and a comparator amplifier is installed to receive a reception signal from the telephone line with the voltage dividing point of the voltage dividing resistor as a reference potential. A transmitting/receiving switching circuit provided at the transmitting/receiving end, which is installed separately from a transmitting signal output circuit for transmitting the transmitting signal to the telephone line via the equivalent resistor, and configured to output the dialing signal from the dialing signal generation source. a dial signal output circuit that receives the dial signal and directly sends it to the telephone line; dial signal detection means that receives the output of the dial signal generation source and detects the presence or absence of the dial signal; output switching means for switching the dial signal output circuit to an operating state when transmitting a dial signal and switching the transmit signal output circuit to an operating state when not transmitting a dial signal; .