JPH02119456A - Call circuit for telephone set - Google Patents

Abstract

PURPOSE:To make the level of a DTMF signal at a receiver constant and to adjust the level of the DTMF signal independently by adding a circuit returning a transmission signal to the side of a receiver circuit. CONSTITUTION:In the case of applying dialing by a DTMF signal, a control signal is inputted to a control terminal 52 to switch analog switches 32, 37 to the position shown in dotted lines in figure. Thus, the DTMF signal is sent to the line from a transmission output amplifier and no voice signal is sent. Moreover, the DTMF signal is outputted to a receiver via an amplifier 39 and a receiver driver 38. Thus, the DTMF signal in the case of dialing is confirmed from the receiver and the sound volume is not affected by a line impedance ZL. Thus, the level of the confirming DTMF tone is not largely changed depending on the installed location.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a telephone communication circuit IC, and particularly relates to ease of designing the volume of monitor sounds such as DTMF signals and hold music.

[Conventional technology]

The use of ICs in telephones has progressed, and ICs have come to be used even in the communication circuits inside telephones.

FIG. 3 shows a circuit in a telephone set when a communication circuit IC is used. Subscriber line T1. Rectifier circuit 1 from T2.
A communication circuit IC4 is connected through the hook switch 2. The communication circuit IC4 has a built-in transmitting amplifier 23, a transmitting signal changeover switch, and a receiving amplifier. Further, a balance network 3 and resistors R1 and R2 are connected to constitute a bridge circuit that operates as a 2-wire to 4-wire converter.

In the telephone set shown in FIG. 3, when making a dial call, the switch 20 in the communication circuit IC is switched to send a DTMF signal to the line. The DTMF signal sent to the line is passed through the balance network 3 or resistor R2 to the receiving amplifier 2.
1, output to the receiver, and the caller receives the
You can check the DTMF signal through. The signal level at which the DTMF signal sent out at this time returns to the receiving amplifier input is determined by the bridge circuit. FIG. 4 shows only the bridge circuit part. Z L / Z s is Z
It is a parallel circuit of L and Zs, and Zl is the AC impedance when looking at the subscriber line side from the middle point 10 in Figure 3, and Zs is the AC impedance when looking at the communication circuit IC from the middle point 11 in Figure 3. be.

Therefore, when the condition ZL/ZllXR2=RIXZa is satisfied (1-), no signal is returned to the receiving circuit.

2 is the AC impedance of the telephone, which is approximately 6 in Japan.
Although it is designed to be 00Ω, 2. is the impedance of the subscriber line, which varies depending on the length of the subscriber line to the exchange and the type of cable used.

Therefore, the bridge never becomes balanced, and the signal always returns to the receiving circuit. However, as explained earlier, Z varies depending on the installation location of the telephone, so the magnitude of the signal returned to the receiving circuit is not constant. For example, the absolute value of line impedance is 2. is 400-170
It changes by about 0, and the frequency characteristics are also large. Therefore, the magnitude of sidetone changes by more than 6 dB.

[Problems to be Solved by the Invention] In the conventional communication circuit mentioned above, the signal returned to the receiving circuit (hereinafter referred to as sidetone) is not constant depending on the installation location of the telephone, so the loudness of the DTMF confirmation sound is It varies greatly depending on the installation location, so it has the disadvantage that it may be too large or too small.

[Means to solve the problem]

According to the present invention, a telephone communication circuit is provided which has a means for transmitting a DTMF signal, a hold tone, etc. to a receiving circuit at a stage before outputting it onto a line when transmitting a DTMF signal, and causing the receiving circuit to output only this signal.

〔Example〕

Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a block diagram of a communication circuit IC showing a first embodiment of the present invention. Preamplifier 30 that amplifies the microphone signal
, a transmitter section consisting of a preamplifier 31 that amplifies the DTMF signal, an analog switch 32 for switching the output signal based on an external control signal, a variable loss circuit 33, and a transmitter output amplifier 34, and a preamplifier 35 that amplifies the receive signal. and a variable loss circuit 36, an amplifier 39 for guiding the sending signal to the receiving circuit, an analog switch 37 for switching between the receiving signal and the sending signal, and a receiver driver 38, a power supply circuit 40, and a variable loss receiving section. It has a control circuit 41 that controls the circuit.

Next, the operation will be explained.

Analog switches 32 and 37 in FIG. 1 operate synchronously by signals from control terminals. Normally, in the talking state, the analog switches 32 and 37 are connected to the solid line in FIG. Therefore, the audio signal from the microphone is sent out from the transmitting output amplifier, and the receiving signal (including sidetone) entering the receiving preamplifier is output to the receiver. Therefore, you can make calls. On the other hand, when dialing using a DTMF signal, a control signal is input to the control terminal 52 and the analog switches 32 and 37 are switched to the dotted line side in the figure. Therefore,
A DTMF signal is sent out from the speech output amplifier to the line, and no audio signal is sent out. Also, the receiver receives the DTMF signal through an amplifier 39. The signal is output through the receiver driver 38.

Therefore, the DTMF signal when dialing can be confirmed from the receiver, and its volume depends on the line impedance Z.
Not affected by L.

FIG. 2 is a block diagram showing a second embodiment of the invention. The configuration is similar to that shown in FIG. 1, but the amplifier 390 in FIG.
The input section of the variable gain amplifier 42 is a variable gain amplifier 42 that can be set externally, and the input of the variable gain amplifier 42 is connected to the signal amplifier 31.
The difference is that it has two systems, one from the output of the other and the other from the external signal input. Therefore, the output level of the DTMF signal from the receiver can be adjusted independently by changing the gain of the variable gain amplifier. Also, since it has an external signal input terminal, it is possible to mix the key confirmation sound.

[Effects of the Invention] As explained above, the present invention provides DTM control at the receiver by adding a circuit that returns the transmitted signal to the receiving circuit side.
It is possible to make the magnitude of the F signal constant regardless of the installation location of the telephone, and to independently adjust only the magnitude of the DTMF signal, which has the effect of greatly improving the designability and quality of the telephone.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
FIG. 3 is a block diagram showing a second embodiment of the present invention, FIG. 3 is a diagram showing an applied circuit of a conventional example, and FIG. 4 is a circuit diagram explaining a bridge circuit that plays the role of 2-wire to 4-wire conversion. It is. 2...Hook switch, 3...Balance network, 4...Telephone circuit IC, 5...
...Microphone, 6...Receiver-21...
... Receiving amplifier, 23 ... Transmitting amplifier, 30
...Transmission preamplifier, 31... Signal preamplifier, 32... Analog switch, 33.
...Variable loss circuit, 34... Sending output amplifier, 35... Receiving preamplifier, 36...
...Variable loss circuit, 37...Analog switch, 38...Receiver driver 39...
...Amplifier, 40...Power supply circuit, 41...
...Control circuit, 42...Variable gain amplifier. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] DTMF is used in telephone call circuits that send out DTMF signals and hold music using a sender circuit that sends voice signals.
A talking circuit for a telephone, characterized in that it has a means for sending the signal to a receiving circuit before outputting the signal to the line only when transmitting a signal, hold tone, etc., and for the receiving circuit to output only the signal. .