JPH04150126A - Telephone terminal equipment - Google Patents

Abstract

PURPOSE:To attain a stable operation at all times by providing a message signal generating means outputting a message signal, 1st and 2nd filters and a pushphone signal detection means on this terminal equipment. CONSTITUTION:A band pass filter 12 is inserted between a voice message generating circuit 11 and a D/A converter 13, and a band pass filter 15 and an AGC (automatic gain control) circuit 16 are inserted between an A/D converter 14 and a DTMF(Dual Tone Multi-frequency) detection circuit 17. Only the frequency component of a pushphone signal in a message signal outputted from the message generating circuit 11 is cut off by a 1st filter 12 and the result is outputted to the line. Furthermore, a 2nd filter 15 is used to extract only a pushphone signal component. Thus, the stable operation without mis-detection is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a telephone terminal device that is provided with means for generating a message signal such as a voice message and means for detecting a touch tone signal.

[Prior Art] Telephone terminal devices that can be operated from a remote location by executing various functions based on touch-tone signals received via a telephone line have been known.

In this type of device, the telephone terminal device performs a predetermined function in response to the caller's operation of a button. As is well known, the button signal is a DTMF (Dual
Tone MultiFrequency) is a signal that has two types of frequency components selected from the four types of high and four types of low groups, and is detected by the DTMF detection circuit installed on the receiving side of the telephone terminal device. There is.

In addition, for example, in systems that use telephone lines to check bank account balances, you can use the telephone terminal installed at the bank or the [Please enter your PIN].

” is sent to prompt the user to input the DTMF signal. In this case, the bank's telephone terminal equipment has DTM
In addition to the F detection circuit, a voice message generation circuit is provided.

[Problems to be Solved by the Invention] In this type of telephone terminal device, as shown in FIG. The incoming signals from the telephone lines Ll and L2 are outputted to the telephone lines Ll and L2, and are received by the receiving terminal R of the LSII via the transformer 3. Here, due to the circuit configuration, the transmission signal from the transmission terminal T goes around to the reception terminal R to some extent.

Such sidetones are not a big problem in normal conversation. However, in this type of telephone terminal device, if the voice message signal or warning sound generated by voice synthesis contains a frequency component of the DTMF signal, the DTMF detection circuit on the receiving side will detect this. However, there is a problem in that it causes malfunction of the telephone terminal device.

Therefore, methods such as echo cancellers have been considered to prevent the signal from circulating from the transmitting side to the receiving side, but echo cancellers are usually a means of adaptively changing the transfer function according to the connection line conditions. D
If implemented using an SP (digital signal processor), it would require only one chip, which would result in a large cost burden.

This invention was made to solve these problems, and provides a telephone terminal device that has an extremely simple configuration, prevents message signals from being passed around to the receiving side, and can always operate stably. The purpose is to provide

[Means for Solving the Problems] The telephone terminal device of the present invention includes a message signal generating means for outputting a message signal, and a touch-tone signal frequency component that is cut only from the message signal output from the message signal generating means. A first filter that transmits the signal to the transmitting side, a second filter that passes only the frequency component of the touch tone signal from the received signal, and touch tone signal detection means that detects the touch tone signal from the output of the second filter. It is characterized by

[Function] According to the second invention, only the touch tone signal frequency component of the message signal output from the message signal generating means is cut by the first filter and then output to the output terminal. Even if the message signal reaches the receiving side as a sidetone, the touchtone signal detection means will not perform an erroneous detection operation because the sidetone does not contain the touchtone signal frequency component.

Further, according to the present invention, the second filter is provided before the push-tone signal detection means, and only the frequency component of the touch-tone signal is extracted by this second filter, so that the touch-tone signal can be detected by the touch-tone signal detecting means at the subsequent stage. This prevents noise other than the frequency components from being mixed in.

Therefore, according to the present invention, a correct touch-tone signal from the line side can always be detected and stable operation can be performed.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a telephone terminal device according to an embodiment of the present invention.

In FIG. 1, LS I l O includes a voice message generation circuit 11, a bandpass filter 12, a D/A converter 13, an A/D converter 14, a bandpass filter 15, and an A/D converter 14.
It incorporates a GC circuit 16 and a DTMF detection circuit 17, and transmits a voice message from the transmission terminal T, and introduces a DTMF signal to the reception terminal R.

The voice message generation circuit 11 outputs a voice message, a signal tone message, etc. for prompting the input of a response message and a touch-tone signal, and is constituted by a voice synthesis circuit. The output of this voice message generation circuit 11 is input to a band pass filter 12 which is a first filter.

The bandpass filter 12 is composed of a digital filter having a transmission zero point in the frequency band of the DTMF signal,
Only the frequency component of the DTMF signal included in the message signal output from the message generation circuit 11 is cut. The output of this bandpass filter 12 is converted from a digital signal to an analog signal by a D/A converter 13, and then sent to a transmission terminal T, a resistor 2 and a transformer 3 as a transmission signal.
The data is transmitted to telephone lines Ll and L2 via the telephone lines L1 and L2.

Further, the reception signal received at the reception terminal R via the telephone lines Ll, L2 and the transformer 3 is converted from an analog signal to a digital signal by the A/D converter 14, and then converted to a second signal by the A/D converter 14.
The signal is input to a bandpass filter 15 which is a filter. The bandpass filter 15 filters D from the received signal.
Only the TMF signal frequency component is passed. The output of the bandpass filter 15 is level-adjusted by an AGC (automatic gain control) circuit 16 and then input to the DTMF detection circuit 15. DTMF detection circuit I5 detects a DTMF signal component included in the received signal.

Among the above configurations, the first filter, the bandpass filter 12, can be configured as follows.

That is, an analog filter having a transmission zero point at a certain specific frequency can be realized by a twin T circuit as shown in FIG. This circuit consists of a T-type low-pass filter consisting of resistors 2I, 22 and a capacitor 23, and a capacitor 2
4.25 and a T-type bypass filter consisting of a resistor 26 are connected in parallel. Here, resistance 21.2
Assuming that the resistance value of 2 is R1, the resistance value of resistor 26 is R/2, the capacitance value of capacitor 24.25 is 01, and the capacitance value of capacitor 23 is 20, the transfer function of this circuit can be expressed by the following equation (1). As shown in Figure 3, the angular frequency ω. A narrow-band notch filter with frequency characteristics that is a transmission zero point can be obtained.

Note that here S is the Laplace operator, (in the case of Fig. 2, q2 When this transfer function is S-Z transformed, It becomes like the expression.

...(1) q2 is fi = 0.25).

(2) below... (2) A digital filter with such a transfer function has the fourth
This can be realized with a circuit as shown in the figure. That is, this filter includes a delay circuit 31.3 that delays the input signal.
2, and coefficients 86+aa! for the input signal and the outputs of the delay circuits 31 and 32, respectively. Multiplying coefficient circuit 33.34.35
, delay circuits 36 and 37 for delaying the output signal, and coefficients applied to the outputs of these delay circuits 36 and 37, respectively.

b! Multiplying coefficient circuits 38 and 39, and coefficient circuits 33 to 3
5, 38, and 39, and an adder 4o that adds the outputs of 5, 38, and 39 and outputs the output signal.

On the other hand, the DTMF signal is composed of four types of frequencies in the high group and four types in the low group, and the frequencies and the buttons are set in a relationship as shown in Table 1 below.

Table 1 Therefore, as shown in Figure 5, by variously changing the filter coefficients of the digital filter in Figure 4, eight types of notch filters with each of the above frequencies as transmission zero points were constructed, and these filters were connected in series. By connecting to the above, it is possible to configure a bandpass filter 12 having transmission zero points at the eight types of frequencies.

It is preferable that the bandpass filter I2 has an attenuation amount of 50 dB or more at ±3% of the frequency of the transmission zero point, and has a narrow band attenuation region.

On the other hand, the second filter, the bandpass filter 15, is configured as follows.

That is, a filter that passes only a specific frequency component can be realized by a parallel resonant circuit consisting of a capacitor 41, a resistor 42, and an inductance 43, as shown in FIG.

The impedance of this resonant circuit can be expressed by the following equation (3).

... (3) In addition, here, S1+ s2 is It is.

Also, Q is the Q value of the resonant circuit, ω　O is resonance is the angular frequency.

Next, by applying sz transformation to equation (3) and adding a zero point to z-'=1, the transfer function of equation (5) below can be obtained.

... (5) Here, r=1-〇/ (2Q), q=r cos
θ, θ−ω. /f, , f8 are sampling frequencies.

A digital filter with such a transfer function has the seventh
This can be realized with a circuit like the one shown in the figure. That is, this filter applies 1/(He”) to the input data D lfi.
a multiplier 51 that multiplies , an adder 52 that takes the output of this multiplier 51 as one input, a delay circuit 53 54 that delays the output of this adder 52 , and these delay circuits 53
．． Coefficient circuits 55 and 56 multiply the output of the adder 54 by coefficients 2q and -r' and supply the outputs as the other input of the adder 52, and the output of the delay circuit 54 is input from the output of the adder 52. The subtracter 57 performs subtraction.

As shown in FIG. 8, the digital filters 61, 62 . . . , 68 are supplied with data D 1m in parallel, and these filters 6
By adding the outputs of 1 to 68 in the adder 69, D
A bandpass filter 15 is configured to pass eight types of frequency components of the TMF signal. Note that it is preferable that this bandpass filter 15 has a passband of approximately ±3% of the touchtone signal frequency.

Next, the DTMF detection circuit 17 will be explained.

As shown in FIG. 9, this circuit consists of eight detection lines 71, 72 .
. . , 78, each detection line 71 to
78 includes a band pass filter 81 that passes only the frequency component to be detected, a rectifier circuit 82 that rectifies the output of the band pass filter 81, and a low pass filter 83 that removes high-frequency noise from the output of the rectifier circuit 82. , and a level detection circuit 84 that compares the output of this low-pass filter 83 with a predetermined threshold level and outputs detection signals DET to DET8.

Next, the operation of the telephone terminal device of the embodiment configured as described above will be explained.

A telephone terminal device connects telephone line L1. When a call from L2 is detected and the call is automatically received, the voice message circuit 11 first outputs a response message such as the name of the called party using synthesized voice. Then, for example, "Please enter your PIN number by operating the button."
A message prompting the input of a DTMF signal is sent. This message passes through a bandpass filter 12, whereby eight types of frequency components constituting the DTMF signal are cut off. The output of the bandpass filter 12 is D/
After being A-converted, it is output from the transmission terminal T of LSI10. The message signal is then sent to the telephone lines L1 and L2 via the resistor 2 and transformer 3.

On the other hand, when the caller operates the push button in response to this message, the DTMF signal corresponding to the button propagates through the telephone lines Ll and L2, and passes through the transformer 3 to the LSI Il.
It is received at reception terminal R of 0. This received signal is A/D
After being A/D converted by the converter 14, it is input to the band pass filter 15, where only the touch tone signal component included in the received signal is passed. When the output of the bandpass filter 15 is input to the AGC circuit 16, the AGC circuit 16 automatically adjusts the amplification factor according to the input signal level of the AGC circuit 16 so that the output level of the AGC circuit is constant. is adjusted to

The output of the AGC circuit 16 is input to the DTMF detection circuit 17. If the transmitted signal contains a DTMF signal, the DTMF detection circuit 17 outputs "1" from two detection lines corresponding to that frequency. Then, predetermined response processing is performed based on the output of this DTMF detection circuit 17.

Incidentally, when a voice message prompting the user to operate the button is sent, the message is also transmitted to the receiving terminal R of the LSI 1O. However, since this message passes through the bandpass filter 12 and has the eight types of frequency components of the DTMF signal described above cut off, it is unlikely that the DTMF detection circuit 17 will be mistakenly detected by the message that has passed around. do not have. In addition, a bandpass filter 15 and an AG
Since the DTMF detection circuit 16 is provided with the C circuit 16, only the touch tone signal frequency component is supplied to the DTMF detection circuit 17. Therefore, there is no possibility that the level detection circuit 84 or the like will malfunction due to extra noise components outside the designated band.

As described above, according to the telephone terminal device of this embodiment, the bandpass filter 12 is inserted between the voice message generation circuit 11 and the D/A converter 13, and the bandpass filter 12 is inserted between the A/D converter 14 and the DTMF detection circuit. The desired effect can be obtained with an extremely simple configuration that only requires inserting the band pass filter 15 and the AGC circuit 16 between the band pass filter 15 and the AGC circuit 17. Moreover, since the bandpass filter 12 shown in FIG. 5 and the bandpass filter 15 shown in FIG. 8 can be realized with an extremely simple configuration, they can be incorporated as part of a DSP for modem processing, for example. It is.

[Effects of the Invention] As described above, according to the present invention, of the message signal output from the message signal generating means, only the frequency component of the touch tone signal is cut by the first filter and then output to the line side. Therefore, even if the message signal reaches the receiving side, the touch tone signal frequency component will not be erroneously detected by the touch tone detection means.

Further, according to the present invention, the second filter is provided before the touch-tone signal detection means, and only the frequency component of the touch-tone signal is extracted by this second filter. This prevents noise other than the frequency components of the touch-tone signal from being mixed in.

From the above, according to the present invention, stable operation without false detection can be realized.

According to the present invention, such an effect can be obtained simply by adding a bandpass filter, so that the circuit configuration does not become complicated and the circuit scale does not increase.

[Brief explanation of drawings]

Figures 1 to 9 are diagrams for explaining a telephone terminal device according to an embodiment of the present invention, with Figure 1 being a block diagram of the main parts, and Figure 2 explaining the configuration of the first bandpass filter. Figure 3 is a graph showing the frequency characteristics of the transfer function of the same filter, Figure 4 is a block diagram of the same filter configured with a digital filter, and Figure 5 shows the actual circuit of the same filter. Block diagram: Figure 6 is an analog circuit diagram for explaining the configuration of the second bandpass filter, Figure 7 is a block diagram of the same filter configured as a digital filter, and Figure 8 is an actual circuit diagram of the filter. FIG. 9 is a block diagram of a DTMF signal, and FIG. 10 is a circuit diagram showing a conventional telephone terminal device. 1.10; LSI, 2. Resistor, 3; Transformer, 11; Voice message generation circuit, 12, 15; Bandpass filter, 13; D/A converter, 14; A/D converter, 1
6. AGC circuit, l7; DTMF detection circuit

Claims (1)

[Claims] (1) Message signal generating means for outputting a message signal; a first filter for cutting only the touchtone signal frequency component of the message signal output from the message signal generating means and transmitting it to the transmitting side; 1. A telephone terminal device comprising: a second filter that allows only frequency components of a touch tone signal to pass; and touch tone signal detection means that detects a touch tone signal from an output of the second filter.