JPS6365759A - Calling current supply circuit - Google Patents

Abstract

PURPOSE:To prevent the mixture of an induced common-mode signal such as a broadcast radio wave as a common-mode signal to high frequencies and a differential signal to a low impedace by connecting an HPF to the reference input of a constant current circuit so as to drive a constant current circuit. CONSTITUTION:When the low frequency of a telephone voice band is inputted, the input signal is smoothed by capacitors CA0, CB0 having a large capacitance and inputted to constant current circuits 3, 4. Thus, a sufficiently high impedance is given to both the lines A, B at the telephone voice band. If an induced common-mode signal is mixed as the radio wave of a medium wave broadcast, capacitors CA1, CB1 of the HPFs 1, 2 are low in the impedance. As a result, the constant current circuits 3, 4 are controlled by said induced common-mode signal and the circuits have a low AC impedance. Moreover, a low impedance is also attained for the differential signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to automatic telephone exchanges, and is particularly used for connecting calls between exchanges. The present invention relates to a communication current supply circuit for supplying communication current between an incoming trunk and an outgoing trunk.

[Conventional technology]

As shown in FIG. 2, conventionally, when supplying communication current between exchanges, direct current is supplied from the communication current supply circuit 11 located at the incoming trunk IOK to the outgoing trunk 30 via the line 20, and then to the outgoing trunk 30. The current is looped in a certain DC loop circuit 31.

Speech signals are combined using a capacitor. Needless to say, the communication current supply circuit 11 and the DC loop circuit 31 have high impedance with respect to AC signals.

As shown in FIG. 3, a conventional communication current supply circuit has used a wire ring having low DC resistance and high AC impedance. When there is guidance from broadcast radio waves, etc., in the wire ring shown in Figure 3, the winding start of the wire ring is opposite for the A line and B line with respect to this induced in-phase signal. Therefore, it is possible to prevent inductance from being generated for common-mode signals.

In other words, the circuit shown in FIG. 3 has a low resistance value because it has only the DC resistance of the windings with respect to the common mode signal.

With the recent reduction in the price of electronic circuit components and the development of electronic circuit technology, an electronic communication current supply circuit as shown in FIG. 4 (Japanese Patent Application No. 66274/1982) was devised.

This is equivalent to FIG. 3 in terms of DC low resistance and AC high impedance functions. However, in Figure 4,
Similar to the differential signal, the in-phase signal arriving at the A terminal and the B terminal has a high impedance.

This results in a difference in the impedance of the line to the common mode signal, and the circuit shown in Figure 3 has no interference with the induced common mode signal.
It can be said that the circuit shown in FIG. 4 is likely to be contaminated with an external induced common-mode signal.

However, there is a problem when in-phase signals induced by broadcast radio waves etc. are mixed in.The circuit shown in Figure 4 uses active elements such as transistors IOA and ICB, so the broadcast waves are easily detected, and the in-phase signal is converted into a differential signal.

Also, in Figure 4, the circuit constants are symmetrical for both the A-line and B-line circuits, but due to manufacturing variations, the circuits are not symmetrical, and the mixed in-phase signal is the same on both the A-line and B-line sides. It is no longer a level, but this difference is converted into a differential signal.

If the mixed in-phase signal level is high, the level converted to a differential signal will also be high, and in the worst case, if the guided AM broadcast wave is detected and the carrier wave is removed, it will return to the normal call signal level. You may be able to hear it.

[Problem that the invention seeks to solve]

As described above, the electronic communication current supply circuit shown in FIG. 4 has the problems of high common-mode impedance and a detection function that is not originally required.

Therefore, in view of the above-mentioned problems, the present invention provides high impedance for differential signals in the telephone voice band, and low impedance for differential signals and common mode signals in high frequencies such as medium wave broadcasting. The present invention provides a communication current supply circuit suitable for computerization.

[Failure to solve the problem]

According to the invention, first and second detection resistors (RAO, RAI and RBO, RBI) respectively detect the line voltages of the first and second lines transmitting one communication current.

first and second low pass filters (CAO and CBO) connected in parallel to the first and second sense resistors, respectively;
) and the equivalent DC voltage from which the AC component of the line voltage has been removed by the first and second low-pass filters are received, respectively, and the current having a magnitude corresponding to the level of the equivalent DC voltage is transmitted to the above. In the communication current supply circuit having first and second constant current circuits (ICA, QA, RA2 and ICB, QB, RB2) that output to the first and second lines, respectively, the first and second lines The first and second high-pass filters (CAI, RA3 ．．
RA4 and CB1. RB3. RB4) is provided between the first and second detection resistors and the first and second constant current circuits, respectively.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention, I
CA, ICB are operational amplifiers, QA, QB are transistors, RAO~4, RBO~4 are resistors, CAo
, 1, CBo.

1 is a capacitor, and J, G, and → are jump terminals.

In this embodiment, the first and second lines A transmitting 9 communication currents are
, H, and first and second sensing resistors RAO, RAI and RBO, RBI, respectively.

first and second low pass filters CAO and CBO connected in parallel to the first and second sense resistors, respectively. Further, the first and second low-pass filters each receive an equivalent DC voltage from which the AC component of the line voltage has been removed, and a current having a magnitude corresponding to the level of the equivalent DC voltage is applied to the first and second low-pass filters. The first and second constant current circuits ICA, QA, and RA2 output to the two lines, respectively.
and has ICB, QB, and RB2. In this embodiment, in a communication current supply circuit having such a configuration (corresponding to the communication current supply circuit in FIG. 4), the high frequency AC components from the first and second lines are first and second high-pass filters CA 1 , RA3 , RA4 and CBI , RB3 that supply the current to the first and second constant current circuits, respectively, without causing the current to be sent to the second low-pass filter;
．． RB4.

The present invention is characterized in that it is provided between the first and second detection resistors and the first and second constant current circuits, respectively.

First, when the low frequency of the telephone audio band in the frequency band of 0.3 to 3.4 kHz is input, CA1. If CB1 is a capacitor with a small capacitance, the impedance will be high, so it can be almost ignored.
O, CBO capacitor p ICA and ICB (
+) The input voltage is well smoothed. ICA, QA.

RA2 (ICE, QB, RB2) constitutes a constant current circuit.

Both the A line and B line sides can have sufficiently high impedance in the telephone voice band.

Next, if we consider the case where an induced in-phase signal of several 100 kHz is mixed in as a radio wave of medium wave broadcasting, CAI and CBI will become low interference and dance, and the effects of 9 CAO and CBO will disappear. In other words, the AC signal input from the A line or B line is R
Bypass CAI and CBI through AO and RB O.

For this reason, the operational amplifiers IOA and I that constitute the constant current circuit
The induced common-mode signal is input to the (+) input of CB, and IOA and ICB drive transistors QA and QB according to this voltage. Therefore, this circuit has low AC impedance. in this case.

It also has low impedance for differential signals. Moreover, since the frequency is far from the normal telephone voice band, it has no effect on the differential signals used.

〔Effect of the invention〕

As explained above, the present invention connects a high-pass filter to the reference input of the constant current circuit and drives the constant current circuit, thereby creating a high impedance for differential signals in the consonant voice band. For high frequencies such as medium wave broadcasting, it has a low impedance with respect to in-phase and differential signals, so it is possible to make it difficult to mix in induced in-phase signals such as broadcast radio waves. Even if a broadcast radio signal is detected, the signal can be suppressed without affecting the differential signal used.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Second
2 is a block diagram showing an example in which the talking current supply circuit of the present invention is used. FIG. 3 is a diagram showing an example of a conventional communication current supply circuit using wire wheels, and FIG. 4 is a diagram showing an example of a conventional communication current supply circuit using an electronic circuit. IOA and ICB are operational amplifiers, and QA and QB are transistors. RAO~4, RBO~4 are resistors, CAo, 1
, CBo, 1 are capacitors and are jumper terminals.

Claims (1)

[Claims] 1) First and second detection resistors that respectively detect the line voltages of the first and second lines that transmit the communication current, and a second detection resistor that is connected in parallel to the first and second detection resistors, respectively. 1 and 2 low-pass filters each receive an equivalent DC voltage from which the AC component of the line voltage has been removed by the first and second low-pass filters, and receive a voltage corresponding to the level of the equivalent DC voltage. In the communication current supply circuit, the communication current supply circuit includes first and second constant current circuits that output currents of 1 to 2 to the first and second lines, respectively. The first and second high-pass filters, which are supplied to the first and second constant current circuits, respectively, without being sent to the first and second low-pass filters, are connected to the first and second detection resistors. and the first and second constant current circuits, respectively.