JPS6312428B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a telephone circuit used in telephones and intercoms.

As shown in FIG. 1, the conventional telephone circuit is constructed such that the telephone circuit 6 is connected to the telephone line terminal 3 by a switch 5 or similar switching means during a telephone call, and when the telephone is not in a telephone call, the switch is connected to the terminal 3. In the usual configuration, the communication path end load is in an open state as the line is opened.

However, as shown in FIG. 2, in a telephone set in which information signals are multiplexed from the main device 2 to the telephone line 1, and a plurality of telephones TEL ₁ and TEL ₂ are connected to the telephone line 1 in branches, etc. , it is necessary to detect information signals from the telephone line 1, whether or not it is in a telephone call state, and these information signals are generally sent by in-band or out-of-band signals. A circuit 4 for separating and extracting speech signals and information signals is provided at the end of the communication path input section. Since such a separation/extraction circuit 4 usually needs to be bidirectional, it is generally constructed of a passive filter. As is well known, such a filter has good matching to input and output impedances within the passband, but deteriorates outside the passband. However, in the case of a telephone configured as shown in FIG. Not only is it impossible to compensate for the passband characteristics, but also the signal level on the communication line 1 becomes unstable, which impairs communication quality.
When considering such matters, in the conventional telephone circuit configuration as shown in FIGS.
The load on the separation/extraction circuit 4 becomes open, and as shown in Figure 3, which shows an example of its impedance characteristics using an LPF as an example, the end impedance of the communication path as a load on the communication line cannot be guaranteed within the passband. There was a problem.

The present invention has been made to solve these drawbacks, and is configured to always keep the impedance at the calling end at a constant value by using an impedance circuit having an impedance equivalently equal to that of the calling circuit. This is a telephone circuit featuring:

The present invention will be explained in detail below with reference to the drawings.

FIG. 4 shows an embodiment of the present invention, in which 1 is a communication line, 3 is a communication line terminal, 4 is a separation/extraction circuit, 5 is a switch, 6 is a communication circuit, 7 is a handset, and 8 is a telephone line.
9 is an information signal modulation/demodulation circuit, 9 is a control circuit, 10 is a control input terminal, and 11 is an impedance circuit. Here, the impedance circuit 11 is configured to have an impedance equivalent to the terminal impedance Z of the communication circuit 6. In the call state, the call circuit 6 is connected to the terminal impedance of the separation/extraction circuit 4 by the switch 5, so the separation/extraction circuit 4 exhibits the desired wave characteristics, and the information signal to the call circuit 6 is This prevents contamination. On the other hand, when the call is not in progress, the impedance circuit 11 is connected by the switch 5 to serve as a load impedance for the separation/extraction circuit 4 in the same manner as the above-mentioned call circuit 6, producing the same effect.

As described above, according to this configuration, since the separation/extraction circuit 4 is always terminated with its matching impedance, the impedance on the telephone circuit side viewed from the communication path terminal 3 is always constant within the passband as shown in FIG. Since the load effect on the communication line 1 remains constant, the information signal from the communication line always inputs and outputs to and from the information signal modulation/demodulation circuit 8 at a constant level, regardless of whether a call is in progress or not. It will be done.

In this embodiment, the separation/extraction circuit 4 is composed of an LPF (low pass filter) and an HPF (high pass filter), but it is also composed of a BPF (band pass filter),
A passive filter such as a BEF (band rejection filter) may be used, or a combination thereof may be used. or,
The same applies to bidirectional active filter circuits. Furthermore, the switch 5 can be replaced by other equivalent means, such as a relay contact or a semiconductor switch operating in the talking state.

On the other hand, the present invention is also an effective means for magnetic type systems in which no communication current is superimposed on the communication line, and although the present invention has been explained here as a telephone circuit, it can also be applied to communication circuits such as general intercoms. It's obvious.

As described above in detail, according to the present invention, it is possible to always keep the impedance at the communication line terminal constant, and the load effect on the communication line can be kept constant. Particularly, it can provide an effective means when a plurality of telephone circuits are connected in a branch manner.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing examples of conventional telephone circuits, FIG. 3 is an example of input end impedance characteristics using an LPF as an example, and FIG. 4 is a block diagram showing an embodiment of the present invention. FIG. 5 is an example of the path-end impedance characteristic of the circuit of the present invention.

Claims (1)

[Claims] 1. In a telephone circuit comprising a separation extraction circuit connected to a communication line so as to multiplex and transmit a communication signal and a control information signal, and a communication circuit connected to the separation extraction circuit, the communication circuit of the separation extraction circuit A switch means is provided so that the terminal on the side from which the signal is taken out is connected to the communication circuit during a call, and connected to an impedance circuit having an impedance equal to the impedance of the communication circuit when the call is not in progress; A telephone circuit characterized in that it is configured to equalize the load effect on a telephone line.