JPS61126893A - Signal transmission circuit - Google Patents

Abstract

PURPOSE:To realize an IC or LSI formation by providing a clamp element at an optional point between the outside of a capacitor and an input terminal of an amplifier, and a point with reference potential. CONSTITUTION:A clamp circuit 15 consists of two diodes 16, 17 connected reversely in parallel, and one of them is earthed between an impedance circuit 6 and an amplification circuit 9 to be equipped in a line. In case a multi- frequency signal is generated in the subscriber's circuit L, the reverse input terminal of an operational amplifier 10 is almost kept at a ground potential due to low impedance of a clamp circuit 15, and the charge charged in a capacitor 7 is discharged through diodes 16, 17 of the clamp circuit 15, so a momentary break time of the multi-frequency signal can be shortened. That is, a momentary break time of the signal is shortened by addition of a clamp element to have a good character as a subscriber's circuit of switchboard and the IC and LSI formation are realized.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a two-wire subscriber circuit; This invention relates to a signal transmission circuit.

[Prior art]

Conventionally, a circuit as shown in FIG. 1 has been considered as this type of signal transmission circuit. In Figure 1C: 1 is a subscriber terminal (telephone), 2 and 3 are 2il! ◎ 4 is a detection circuit that detects the differential signal (balanced signal) output from the telephone 1, and 5 is a detection circuit that detects the differential signal (balanced signal) output from the telephone 1, and 5 connects the balanced signal to the unbalanced signal f. The balanced/unbalanced conversion circuit 6 is an impedance circuit consisting of a capacitor 7 and a resistor, and has the function of removing the DC component contained in the output signal of the balanced/unbalanced conversion circuit 5. Further, 9 is an amplifier @ circuit which includes an operational amplifier 1o which applies the output of the Innovidance circuit 6 to its inverting input terminal and whose non-inverting hexagonal terminal is grounded, an output terminal 11, and the output terminal 1.
1 and an inverting input terminal of an operational amplifier 1o, and power supply terminals 13 and 14. This type of signal transmission circuit can convert a signal (balanced signal) output from a telephone into an unbalanced signal and send the signal to other devices with an arbitrary gain. However, for example, If the telephone is a push-button type, pressing the button may output a multi-frequency signal and change the DC resistance, and this change in resistance will also change the direct current flowing through the telephone, causing a difference in the subscriber line L. dynamic signal (
The balanced signal) has a waveform as shown in FIG. 2 (JL). Since the signal generated by the resistance change is a multi-frequency signal (a large voltage change), if the power supply voltage of the operational amplifier 10 is low in the circuit configuration shown in FIG.
The disadvantage is that the dynamic range is insufficient and instantaneous interruptions of multi-frequency signals occur. (Waveform in FIG. 2(b)) This instantaneous interruption time t is determined by the innovidance of the impedance circuit 6, the impedance of the impedance element 12, and the dynamic range of the operational amplifier 10. The impedance of the element 12 is large, that is, the discharge time constant of the charge accumulated in the capacitor 7c is large, and the power supply voltage of the operational amplifier 10 is low (±5 V).
The instantaneous interruption time t becomes longer.

[Purpose of the invention]

It is an object of the present invention to provide a signal transmission circuit that eliminates the above-mentioned drawbacks, has good characteristics as a subscriber circuit of a telephone exchange, has a simple circuit configuration, and can be implemented as an IC or LSI. .

[Structure of the invention]

The present invention provides a subscriber terminal [a detection circuit that detects a balanced signal generated in a connected two-wire subscriber line, a balanced/unbalanced conversion circuit that converts the output of the detection circuit into an unbalanced signal, The balanced/unbalanced conversion circuit consists of an impedance circuit including two connected capacitors as series elements, and an amplifier that applies the output from the impedance circuit to one input terminal and applies a reference potential to the other input terminal. The device is characterized in that a C Niklanop element is provided between an arbitrary point between the output side of the capacitor and the input terminal of the amplifier and the reference potential.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. Third
The figure is a circuit diagram showing one embodiment of the present invention. In addition, K1
Components with the same reference numerals as those shown in the figures have the same functions, and their explanations will be omitted. The difference from the conventional structure is that a ring circuit 15 is added. The clamp circuit 15 consists of two diodes 16 and 17 connected in antiparallel, and is interposed in parallel between the impedance circuit 6 and the amplifier circuit 9 (one of which is grounded).

According to the circuit configuration according to this embodiment≦2, FIG. 2 (JL)
Even if a signal like that shown in is generated on subscriber line L,
The inverting input terminal of the operational amplifier 10 is kept at approximately the ground potential C2 by the low impedance C2 of the clamp circuit 15, and the charge stored in the C2 capacitor 7 is discharged through the diode 16゜17 of the clamp circuit 15. Therefore, C2, the instantaneous interruption time of multi-frequency signals can be shortened. This is because the impedance of the diode is extremely small, so the discharge time constant is small.

In this example, an example is shown in which an anti-parallel connection circuit of diodes is used as the clamp element, but other known clamp circuits such as a clamp circuit using a field effect transistor, a combination of a diode and a voltage source, or a two-amp circuit can also be used. It goes without saying that the present invention can be applied regardless of the configuration of the amplifier element.

Note that the voltage drop in the clamp circuit (approximately 0.7 in this example)
5V) should be equal to or higher than the maximum AC signal level at the connection point of the clamp circuit.In this embodiment, the clamp circuit is connected to the inverting input terminal of the operational amplifier, and 0.75V is sufficient. Furthermore, the connection position of the Clapp circuit is not limited to the input point C of the amplifier, but the same effect can be obtained at any position from the amplifier side of the capacitor 7 included as a series element to the impedance circuit 6t'' to the input point of the amplifier.

〔Effect of the invention〕

As explained above, by adding a clap element to the present invention, the instantaneous signal interruption time can be shortened, and the present invention has good characteristics as a subscriber circuit of a telephone exchange, and it can be integrated into an IC or LSI.
This has the effect of making it possible to realize

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional signal transmission circuit, and Figure 2 (a
), (b) is a schematic diagram showing the input and output waveforms of the circuit shown in FIG. 4...detection circuit, 5
...Balanced/unbalanced conversion circuit, 6... Impedance circuit, 7... Capacitor, 8... Resistor, 9... Amplification circuit, 10... Operational amplifier, 15... Clamp circuit, 16.17...Diode, L...2-wire subscriber line.

Claims (1)

[Claims] a detection circuit that detects a balanced signal generated in a two-wire subscriber line connected to a subscriber terminal; a balanced/unbalanced conversion circuit that converts the output of the detection circuit into an unbalanced signal; It consists of an impedance circuit that includes a capacitor connected to a conversion circuit as a series element, and an amplifier that applies the output from the impedance circuit to one input terminal and a reference potential to the other input terminal, and from the output side of the capacitor. A signal transmission circuit characterized in that a clamp element is provided between an arbitrary point up to the input terminal of the amplifier and the reference potential.