JPS6394752A - Telephone set circuit - Google Patents

Abstract

PURPOSE:To suppress the bypass from a transmitter to a receiver in both extension and external line talking states by connecting an extension or external line balancing circuit network to a side tone prevention circuit respectively so as to balance each line impedance in the extension or external line talking state. CONSTITUTION:When a handset of a key telephone set is hooked off, a hook switch 7 is turned on, no external line is selected and an external switch 8 is turned off, then a control circuit 9 detecting it drives a switching circuit 4 to connect an extension balancing circuit network 5 to a side tone prevention circuit 1. When the extension balancing circuit network 5 is already connected to the circuit 1, it is held. When the external line is selected and the external line switch 8 is turned on, the control circuit 9 detects the on-state to drive the switching circuit 4 thereby connecting the external line balancing circuit network 6 to the side tone prevention circuit 1 and disconnecting the extension balancing circuit network 5 from the side tone prevention circuit 1.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a telephone circuit for a button telephone.

[Conventional technology]

Conventionally, this type of telephone circuit has had a fixed side sound protection circuit network for both internal and external calls.

[Problem that the invention seeks to solve]

-L The telephone circuit of the conventional key telephone described above has the same side sound protection circuit for both internal and external calls, so when making an internal call, the impedance seen when looking at the other party's extension phone and the central office during an external call are Because there is a difference in impedance when looking at the side, it is difficult to balance both impedances with the same side sound prevention circuit, and it is said that it is not possible to suppress noise surrounding side sound during both internal and external calls. There are drawbacks.

[Means for solving problems]

The telephone circuit of the present invention includes a balanced circuit network for extension lines, a balanced circuit network for external lines, and when an extension line is selected, a balanced circuit network for extension lines.
and connecting means for connecting each of the balanced circuit networks for the outside line to the side sound protection circuit when the outside line is selected.

Therefore, during both internal and external calls, the impedances between the line side and the telephone side are balanced, and interference from the transmitter to the receiver can be suppressed.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the telephone circuit of the present invention.

This embodiment includes a side sound protection circuit 1 connected to terminals L1 and L2 connected to a central office line, a transmitter 2, a receiver 3 connected to the protection side sound circuit 1, and a side sound protection circuit. 1, a balanced circuit network for internal lines 5, a balanced circuit network for external lines 6, a control circuit 9, a hook switch 7, and an external line switch connected to the control circuit 9, respectively. It consists of 8.

Next, the operation of this embodiment will be explained. When the handset of the button telephone is picked up, the hook switch 7 is turned on, and if no outside line is selected and the outside line switch 8 is off, the control circuit 9 detects this and the switching circuit 4
is driven to connect the extension balanced circuit network 5 to the side sound protection circuit 1. Of course, if the extension balanced circuit network 5 is already connected to the side sound protection circuit l, it is maintained. Further, when the outside line is selected and the outside line switch 8 is on, the control circuit 9
detects this ON state, drives the switching circuit 4 to connect the external line balanced circuit network 6 to the side sound protection circuit 1, and disconnects the internal line balanced circuit network 5 from the side sound protection circuit 1.

〔Effect of the invention〕

As explained above, the present invention enables internal and external line calls by connecting the internal line or external line balanced circuit networks to the side sound protection circuits so as to balance the respective line impedances depending on the internal line or external line call status. In both states, there is an effect of suppressing interference from the transmitter to the receiver.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the telephone circuit of the present invention. 1... side sound protection circuit, 2... transmitter, 3...
Receiver, 4... Switching circuit, 5...
- Balanced circuit network for internal lines, 8... Balanced circuit network for external lines, 7... Hook switch, 8... External line switch, Ll, L2... Terminals. Figure 1

Claims (1)

[Claims] In the telephone circuit of a button telephone, there is a balanced circuit network for internal lines, a balanced circuit network for external lines, a balanced circuit network for internal lines when an internal line is selected, and a balanced circuit network for external lines when an external line is selected. and connecting means for connecting to the circuit.