JPH082065B2 - Telephone line amplitude equalization circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a telephone line amplitude equalization circuit suitable for use in compensating for attenuation of a transmission signal in a telephone line.

"Prior Art" As is well known, since a telephone line has an inherent attenuation characteristic, it is necessary to compensate the signal amplitude according to the attenuation characteristic of the line. FIG. 5 is a circuit diagram showing a configuration of a conventional amplitude equalization circuit used for such an application. In the figure, 1 is an operational amplifier whose non-inverting input terminal is grounded, and four types of characteristic adding circuits 2a to 2d are connected to the inverting input terminal via switches S1 to S4, respectively. The characteristic adding circuit 2a is composed of a resistor, and the characteristic adding circuits 2b to 2d are each composed of a mixed circuit of a resistor and a capacitor. In this case, one of the switches S1 to S4 is turned on to select one of the characteristic adding circuits 2a to 2d. Figure 6 (a)
Is 0 dB attenuation on the telephone line based on 1.5 KHz,
The attenuation characteristics in the case of 4 dB, 8 dB, and 12 dB are shown together with the level set to 0 dB at 1.5 kHz. FIG. 6B shows the amplification characteristic of the amplitude equalization circuit when the characteristic adding circuits 2a to 2d are selected, and the characteristic shown in FIG. 6A is corrected. The attenuation characteristic of the telephone line is determined based on 1.5 KHz as shown in the figure. Also, the actual attenuation characteristics have various slopes depending on the length of the subscriber cable that connects the central office and the home phone, but for convenience, 0 dB, 4 dB, 8 dB,
It is treated as belonging to any one of the four types of attenuation characteristics of 12 dB.

"Problems to be Solved by the Invention" In the above-mentioned conventional amplitude equalization circuit for a telephone line, it is necessary to previously provide a large number of characteristic adding circuits according to the attenuation characteristics of the telephone line, which complicates the configuration. There was a drawback. Further, since the configuration is such that one of the preset characteristics is selected, there is a drawback that the gain setting can be performed only in stages, and it cannot be applied when intermediate characteristics of each stage are required.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide an amplitude equalization circuit for a telephone line which does not need to have a large number of individual characteristic adding circuits and can obtain an arbitrary compensation characteristic. Has an aim.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a differentiating circuit to which an input signal having an attenuation characteristic peculiar to a telephone line is supplied, and a low circuit to which the input signal is supplied. A passband circuit and an addition point for adding the output signals of the differentiating circuit and the lowpass circuit, and the gain characteristic of at least one of the differentiating circuit and the lowpass circuit is used as the attenuation characteristic of the telephone line. It is characterized in that the attenuation characteristic of the telephone line is compensated at the addition point by adjusting in accordance with.

"Operation" The characteristic of the signal obtained at the addition point is the sum of the respective characteristics of the differentiating circuit and the low-pass circuit, and the characteristic is that the gain increases substantially in proportion to the frequency with a slope determined by the relationship of the respective characteristics. Becomes This characteristic can be changed by adjusting the gain of any one of the differentiating circuit and the low-pass circuit, whereby the attenuation characteristic of the telephone line can be appropriately compensated.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 5 is an input terminal, which is connected to each input terminal of the differentiating circuit 6 and the low-pass circuit 7. The differentiating circuit 6 and the low-pass circuit 7 are configured by using, for example, an operational amplifier, a resistor, and a capacitor, and the internal resistor or capacitor is variably configured so that the gain of the circuit can be adjusted. . The respective output signals of the differentiating circuit 6 and the low-pass circuit 7 are supplied to the addition point 8 to be added, and the signal obtained at the addition point 8 is supplied to the output terminal 9.

In the above configuration, the characteristic of the differentiating circuit 6 is shown in FIG.
If the characteristics of the low-pass circuit 7 are as shown in FIG. 7B, the frequency characteristics of the signal obtained at the addition point 8 are shown by the solid line in FIG. As shown in, the characteristic is a combination of the frequency characteristics of the differentiating circuit 6 and the low-pass circuit 7, and the amplification characteristic has a substantially constant slope with 1.5 KHz as a reference. If the characteristics of the differentiating circuit 6 and the low-pass circuit 7 are the characteristics shown in FIGS. 3 (a) and 3 (b), respectively, the combined characteristics will be the characteristics shown in FIG. 3 (c), with 1.5KHz as the reference. In addition, the amplification characteristic has a larger inclination than in the case of FIG.

Since the slope of the combined characteristic can be changed arbitrarily and continuously by adjusting the gains of the differentiating circuit 6 and the low-pass circuit 7, the gain characteristic should be adapted to the attenuation characteristic of the telephone line. You can

In the above embodiment, the differentiating circuit 6 and the low-pass circuit 7 may each be composed of digital filters. Here, FIGS. 4 (a) to 4 (c) are diagrams showing the impulse response of each part of the circuit when the characteristics shown by the solid line in FIG. 4 (e) are realized by a digital filter. As is well known, the impulse response of the circuit in which the characteristics of the differentiating circuit 6 and the low-pass circuit 7 are added is the impulse response of each circuit added in terms of time. Therefore, the impulse response of the differentiating circuit 6 is the fourth
When the impulse response of the low-pass circuit 7 is the characteristic shown in FIG. 4 (b) and the characteristic shown in FIG. 4 (b), the impulse response at the addition point 8 is shown in FIG. 4 (c). As shown.

Further, when configured by a digital filter, the gain setting of each circuit can be set to an arbitrary value by setting the coefficient in the digital filter, and there is an advantage that the change can be made extremely easy.

[Advantages of the Invention] As described above, according to the present invention, a differentiating circuit to which an input signal having a characteristic of attenuation in a telephone line is supplied, a low-pass circuit to which the input signal is supplied,
An adding point for adding the output signals of the differentiating circuit and the low-pass circuit, and adjusting the gain of at least one of the differentiating circuit and the low-pass circuit according to the attenuation characteristic of the telephone line. As a result, the attenuation characteristic of the telephone line is compensated at the addition point,
There is an advantage that it is not necessary to provide a large number of individual characteristic adding circuits, the configuration can be simplified, and an arbitrary compensation characteristic can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention,
2 and 3 are characteristic diagrams showing the characteristic of the same embodiment, FIG. 4 is a diagram showing an impulse response when the same embodiment is constituted by a digital filter, and FIG. 5 is a conventional amplitude etc. FIG. 6 (a) is a characteristic diagram showing the attenuation characteristic of the telephone line, and FIG. 6 (b) is a characteristic diagram showing the amplification characteristic of the amplitude equalizing circuit of FIG. . 5 ... input terminal, 6 ... differential circuit, 7 ... low-pass circuit, 8 ... adding point, 9 ... output terminal.

Claims (3)

[Claims] 1. A differentiating circuit supplied with an input signal having an attenuation characteristic peculiar to a telephone line, a low-pass circuit supplied with the input signal, and output signals of the differentiating circuit and the low-pass circuit. An addition point for adding, and adjusting the gain of at least one of the differentiating circuit and the low-pass circuit according to the attenuation characteristic of the telephone line, so that the attenuation characteristic of the telephone line at the addition point. A telephone line amplitude equalization circuit characterized by compensating for the above. 2. The compensation of the attenuation characteristic is performed by adjusting the gains of the differentiating circuit and the low-pass circuit so that the level is equal over the entire band. The telephone line amplitude equalization circuit described in. 3. The differentiating circuit and the low-pass circuit are constituted by a digital filter, and the gain of the differentiating circuit and the low-pass circuit is varied by setting a coefficient of the digital filter. A telephone line amplitude equalization circuit according to claim 1.