JPH05219538A - Charging signal reception circuit - Google Patents

Abstract

PURPOSE:To suppress distortion in a voice signal and to set a prescribed PBX termination impedance by inserting a parallel LC filter in series with a signal line at a pre-stage of an electronic choke and inserting a series LCR filter in parallel at a pre-stage of the filter. CONSTITUTION:Since a DC current flows to an inductance L in a parallel filter circuit 3 comprising an L1 and a CO, the circuit 3 is inserted to a pre-stage of an electronic choke circuit 1 and acts like a filter with respect to a charging signal while supplying a station current is supplied to the filter. The filter is used to prevent a voltage over a dynamic range from being applied to the electronic choke thereby suppressing distortion of a voice signal. Furthermore, no DC current flows to a capacitor C3 of a series filter circuit 7. Thus, when the resonance frequency of the circuit 7 is selected equal the charging signal frequency, the resistance is made zero, and a resistor R5 is inserted in series with the filter to obtain a desired impedance and the resistance is selected properly to obtain a desired PBX side impedance with respect to the charging signal frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a billing signal receiving circuit transmitted from a central office in a central office trunk used in a PBX. The central line trunk of the PBX is connected to the subscriber line trunk of the central office switch, and during a call with the subscriber of the central office switch, a charging signal corresponding to the usage frequency by distance and time from the central office switch is received, The call charge for each calling subscriber is counted by the billing device.

Since the PBX station line trunk receives a charging pulse during a call, it does not affect the call as a noise to the subscriber during the call and does not interfere with the interface with the station line. As you can see in the circuit configuration of the trunk. In particular, when connecting the PBX to a station line overseas, it is necessary to construct a circuit corresponding to the interface and charging frequency corresponding to the situation of the station in that country.

The billing signal is a signal transmitted from a station to a telephone or an exchange during a call according to the frequency of use.
There are two types of signals, vertical signals and horizontal signals,
This device detects a billing signal of a lateral signal that adversely affects a voice signal (horizontal direction, normal mode),
Since the voice signal is also in the lateral direction, a high frequency signal is usually used so that the user cannot hear the billing signal even during a call. For example, 12KH in Australia and Spain
16KHz signal is used in z, Finland, etc.

[0004]

2. Description of the Related Art FIG. 4 and FIG. 5 show block diagrams of a conventional PBX office line trunk. 4 shows the case where the filter circuit is provided after the hybrid circuit, and FIG. 5 shows the case where the filter circuit is provided before the hybrid circuit. In the figure, 21 is an electronic choke circuit, 22 is a hybrid circuit, 23 is a filter circuit, 24 is a codec circuit, 25 is a differential amplifier circuit, and 26 is a billing signal receiving circuit.

The electronic choke circuit 21 has a high resistance in terms of alternating current and a low resistance in terms of direct current, and forms a direct current loop for the station side. The capacitor C is for DC cutting, the transformer T is for AC conversion, and the hybrid circuit 22 is 2 wires /
This circuit has a 4-wire conversion function. The filter circuit 23 has a function of removing a billing signal superimposed on a voice signal, and the codec circuit 24 is a CODER / DECODER.
The differential amplifier circuit 25 forms a differential amplifier with a resistor and an operational amplifier, and the charging signal receiving circuit 26 has a function of determining whether or not the input signal is a signal to be detected and notifying the control unit.

The difference between FIG. 4 and FIG. 5 is the insertion position of the filter circuit 23. In FIG. 4, only a passive element is used in the hybrid circuit 22 or a power supply that can withstand a large-amplitude charging signal input. When using active devices with voltage, a filter is inserted to remove the charging signal only to the input of the CODEC. In the case of FIG. 5, the hybrid circuit 22 cannot withstand the input of a large-amplitude charging signal. In such a case, a filter is inserted in the preceding stage of the hybrid circuit 22.

This hybrid circuit 22 is provided with terminations seen from the station side, and has resistors R1, R2, R3, R4 and operational amplifiers.
The billing signal appearing at both ends of the terminating resistor is sent to the billing signal receiving circuit 26 by the differential amplifier circuit 25 composed of AMP, and the billing signal is detected. FIG. 6 shows a state waveform diagram in which the billing signal superimposed on the voice signal is removed through the filter circuit 23. Voice signal is 300Hz-3.4KHz, billing signal is 12KH
z or 16 KHz, the billing signal is superimposed on this audio signal, and the billing signal is
Only 0Hz to 3.4KHz audio signals are transmitted.

The basic circuit configuration of the electronic choke circuit 21 is
It consists of a resistor R6, a capacitor C4 and a transistor TR, the dynamic range of which is the collector-base voltage V _CB of the transistor TR. In the circuit of FIG. 4 of the conventional example 1, since the filter circuit 23 is inserted in the subsequent stage of the electronic choke circuit 21, the amplitude of the charging signal superimposed on the voice signal becomes _{equal to} or _larger than the dynamic range V _CB of the electronic choke circuit 21. In that case, there is a problem that the audio signal after the billing signal is removed by the filter is clipped. In FIG. 6, the waveform clipped by the dynamic range V _CB of the electronic choke and the waveform after it is filtered are shown.

The conventional example 2 has been devised to solve the problem of the conventional example 1. FIG. 7 shows a block diagram of Conventional Example 2. In the figure, 11 is an electronic choke circuit, 12 is a hybrid circuit, 13 is a filter circuit, 14 is a codec circuit, 15 is a differential amplifier circuit, and 16 is a billing signal receiving circuit. The difference from the conventional example 1 is that the filter circuit 13 is inserted in the preceding stage of the electronic choke circuit 11.

As a result, the amplitude of the charging signal can be made sufficiently smaller than the dynamic range V _CB of the electronic choke circuit 11. The billing signal is fetched from the differential amplifier circuit 15 from the preceding stage of the filter circuit 13, and the billing signal receiving circuit 16
Send a billing signal to. In FIG. 7, the filter circuit
13 includes a capacitor C0 and an inductor L1, and the differential amplifier circuit 15 includes capacitors C1 and C2, resistors R1, R2, R3 and R4, and an operational amplifier AMP. The capacitors C1 and C2 are for removing the DC component from the Tip / Ring line.

The inductor L1 and the capacitor C0 together form an LC filter for the charging signal. This resonance frequency is the same as the frequency of the charging signal, and if the frequency of the charging signal is F, then L and C are

[0012]

[Equation 1]

To be Since this LC filter allows a DC current to flow toward L, it can be inserted in the front stage of the computerized choke to serve as a filter for the charging signal while allowing a local current to flow. With this LC filter, it is possible to prevent a voltage above the dynamic range V _CB from being applied to the computerized choke and prevent distortion or the like from occurring in the audio signal.

[0014]

Since the regulation of the level of the charging signal is the level between the Tip / Ring lines, the charging signal is
Input to the billing signal receiving circuit 16 from the Tip / Ring line using the differential amplifier circuit 15. Since the charging signal superposed on the audio signal in the front stage of the LC filter 13 has a dynamic range V _CB or less in the latter stage of the LC filter 13, distortion of the voice signal does not occur.

However, P viewed from the charging signal source on the station side
The impedance of the BX becomes high due to the inserted LC filter, and there is a problem that impedance matching with the output impedance inside the local charging signal generation source of several hundred Ω is usually not achieved. For example, in Finland, a termination impedance of 150 to 400 Ω is required for a charge frequency of 16 KHz. In order to attenuate the charging signal, the LC filter is usually several KΩ. Therefore, the circuit of Conventional Example 2 is out of specifications.

In the present invention, an L choke circuit is provided at the front stage of the electronic choke circuit.
When the C filter is inserted, the purpose is to set the termination impedance of the PBX viewed from the station side with respect to the charging signal frequency to a desired value.

[0017]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, 1 is an electronic choke circuit, 2 is a hybrid circuit, 3 is a parallel filter circuit, 4 is a codec circuit, 5 is a differential amplifier circuit, 6 is a billing signal receiving circuit, and 7 is a serial filter circuit. The serial filter circuit 7 is an LC filter whose resonance frequency is the same as the frequency of the billing signal. A resistor that satisfies the required PBX side impedance for the billing signal is connected in series to form an LCR filter. It is inserted between the rings so that the PBX side terminating impedance standard with respect to the charging signal frequency is satisfied.

[0018]

[Operation] Let L1 be the inductor of the parallel filter circuit 3 and C0 be the capacitor, and let the inductor of the series filter circuit 7 be
Resonance frequency F ₀ of each filter circuit is L2, capacitor is C3 and resistor is R5.

[0019]

[Equation 2]

Set L1, C0 and L2, C3 so that By selecting L and C so that the resonance frequency F ₀ becomes the frequency of the charging signal, that is, 12 KHz, it is possible to perform the filter circuit operation at the charging frequency.

That is, the parallel filter circuit 3 composed of L1 and C0 allows direct current to flow toward the L side, and therefore the electronic choke circuit 1
It is possible to configure a filter for the billing signal while inserting the station current by inserting the filter in the preceding stage. With this filter, it is possible to prevent a voltage above the dynamic range V _CB from being applied to the computerized choke and prevent distortion or the like from occurring in the audio signal.

Series filter circuit 7 consisting of L2, C3 and R5
Since a direct current does not flow due to the capacitor C3, the resonance frequency of this filter is set to be the same as the frequency of the billing signal, so ideally the resistance is 0 for the same frequency as the billing signal, and the desired impedance In order to obtain the above, by inserting the resistor R5 in series with the filter and setting an appropriate resistance value, it is possible to satisfy the impedance standard on the PBX side with respect to the charging signal frequency.

[0023]

FIG. 2 shows a block diagram of an embodiment of the present invention. In the figure, the same numbers as in the principle configuration diagram of FIG. 1 indicate the same circuits. C, C0, C1, C2, C3 and C4 are capacitors, R1, R2, R3, R4, R5 and R6 are resistors, L1 and L2 are inductors, T is a transformer, TR is a transistor and AMP is an operational amplifier. Capacitor C is for cutting the DC current supplied from the station side, and C1 and C2 are for extracting only the AC component after removing the DC component from the Tip / Ring line. C1, C2, R
A differential amplifier is composed of 1, R2, R3, R4 and AMP. L1,
C0 is a parallel filter, and L2, C3, and R5 are serial filters, which form a filter for the charging signal.

The frequency characteristic of the filter circuit is shown in FIG. FIG. 3A is a frequency characteristic of the parallel filter, FIG.
(B) shows the frequency characteristics of the serial fitter. Since L1 and C0 form a low impedance and L2, C3 and R5 form a high impedance with respect to the voice frequency, the frequency of the charging signal is 12
KHz has almost no effect on voice. Here, the resistor R5 is a resistor required only to satisfy the standard, and is not necessary when the value of R5 is 0, that is, the standard is satisfied without the resistor R5.

The billing signal frequency input to the differential amplifier circuit 5 is differentially amplified by the operational amplifier AMP, converted into an on / off billing signal by the billing signal receiving circuit 6, and input to the control unit. The charging signal superimposed on the audio signal input to the electronic choke circuit 1 is controlled by the parallel filter circuit 3 and the series filter circuit 7, and the transistor TR
Since a voltage over the dynamic range V _{CB of}
The voice signal is not distorted and is not affected by charging signal noise.

[0026]

According to the present invention, since the parallel LC filter is inserted in series with the signal line in front of the electronic choke, the amplitude of the charging signal does not exceed the dynamic range, so that the waveform distortion of the voice signal does not occur. Further, since the serial LCR filter is inserted in parallel with the signal line before the parallel LC filter, the termination impedance of the PBX viewed from the station side with respect to the charging signal frequency can be set to a desired value.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention.

FIG. 2 is a block diagram of an embodiment.

FIG. 3 is a frequency characteristic diagram of the filter circuit.

FIG. 4 is a block configuration diagram of Conventional Example 1 (No. 1)

FIG. 5 is a block diagram of the conventional example 1 (No. 2)

FIG. 6 is a state waveform diagram of a billing signal

FIG. 7 is a block configuration diagram of Conventional Example 2.

[Explanation of symbols]

 1,11,21 Electronic choke circuit 2,12,22 Hybrid circuit 3, Parallel filter circuit 4,14,24 Codec circuit 5,15,25 Differential amplifier circuit 6,16,26 Charge signal receiving circuit 7, Series filter Circuit 13, 23 Filter circuit

Claims (1)

[Claims] 1. An electronic choke circuit (1) is provided with an LC parallel filter circuit (3) in series in front of it, and a differential amplifier circuit (5) and a billing signal receiving circuit (6) are used for a tip line / ring.
In a PBX office line trunk that receives a billing signal during a call from a terminal, a serial filter circuit (7) composed of LCR is provided in parallel with the office line Tip / Ring terminal in front of the parallel filter circuit (3). (7) consists of an LC filter whose resonance frequency is the same as the frequency of the billing signal, and a resistor that satisfies the required PBX-side impedance for the billing signal is connected in series to form an LCR filter.
Insert between the Tip / Ring terminals to connect to the charge signal frequency PB
A billing signal receiving circuit, characterized in that it is configured so as to satisfy the X-side terminating impedance standard.