JPH05252316A - Accounting signal sending circuit - Google Patents

Abstract

PURPOSE:To check the transmission of noise generated at the instance of the sending of an accounting signal or the stop of its sending to an opposite station by setting up the switching time of an accounting signal to a value minimizing the amplitude of the accounting signal by a timing adjusting circuit. CONSTITUTION:This accounting signal sending circuit is provided with an oscillation circuit 1 for outputting a rectangular wave signal having frequency several times that of an accounting signal, a frequency dividing circuit 2 for outputting a rectangular wave signal whose frequency is divided up to the frequency of the accounting signal, a low pass filter 3 for extracting a sine wave signal, an analog switch 5 for controlling the output of the filter 3, and a timing adjusting circuit 15 for setting up the switching time of the switch 5. The circuit 5 consists of a delay circuit 7 for outputting a signal delayed from an input signal, a waveform shaping element 8 for sharping a waveform and a flip flop circuit 9 for controlling the accounting signal synchronously with the rise or the face of the signal. Namely the switching time of the accounting signal can be optionally set up by the circuit 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a billing signal transmitting circuit in a PCM terminal device for transmitting a billing signal to a connected public telephone.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional billing signal transmitting circuit, and FIG. 6 shows signal waveforms of respective parts in this circuit. That is, as shown in FIG. 5, the conventional billing signal transmission circuit includes an oscillator circuit 17 that outputs a rectangular wave signal having a frequency several times as high as the billing signal.
A frequency divider circuit 18 for outputting a rectangular wave signal obtained by dividing the output signal of the oscillator circuit 17 to an arbitrary billing signal frequency; a low pass filter 19 for extracting a sine wave signal from the output signal of the frequency divider circuit 18; An analog switch 21 for controlling transmission of the output signal of the low-pass filter 19 is provided.

In this billing signal transmission circuit, the oscillation circuit 17 outputs nf0 when the billing signal frequency is f0 (H _Z ).
A rectangular wave signal with a frequency of (H _Z ) is output. The output signal of the oscillator circuit 17 is supplied to the frequency divider circuit 18 as shown in FIG.
The charge signal f0 (H _Z ) as shown in (a) is divided by 1 / n. Since the output signal of the frequency dividing circuit 18 is a collective wave of a sine wave signal whose fundamental wave is the charging signal frequency f0 (H _Z ) and a sine wave signal of an odd multiple thereof, the low pass filter 19 outputs 3f0 ( The harmonics above H _Z ) are removed and a sine wave signal is obtained.

The sine wave signal extracted by the low-pass filter 19 is a signal extracted with reference to V1 / 2 (V), where V1 is the amplitude of v1 of the signal shown in FIG. 6 (a). Therefore, the DC component is removed by the capacitor 20, and the sine wave signal v2 shown in FIG. 6B with reference to the ground GND is obtained. This sine wave signal v2 is sent to the analog switch 21 and is transmitted to the output terminal depending on whether the logic value of the billing signal control terminal 24 that controls switching of the switch is "1" or "0".

A part of the signal output from the analog switch 21 is output to the 2-wire subscriber line terminal 26 via the 2W-4W conversion circuit (2-wire 4-wire conversion circuit) 27,
The remaining part of the signal determined by the characteristics of the 2W-4W conversion circuit 27, that is, the transformer hybrid loss, is transferred from the 4W sending side terminal connected to the analog switch 21 to the 4W receiving side to which the low pass filter 28 is connected. Sent to the terminal.

[0006] In general the frequency band of the speech signal used in the telephone line is 300～3400H _Z, since the frequency band of the metering signal is 12KH _Z or 16KH _Z,
It is difficult to uniformly reduce the trans-hybrid loss in both frequency bands. Therefore, in the charging signal frequency band, in order to suppress the signal transmitted from the 4W sending side terminal to the 4W receiving side terminal of the 2W-4W conversion circuit 27, the analog low pass filter 28 is used to play the charging signal. The amount of transmission to the side is reduced.

[0007]

In the conventional billing signal sending circuit, the timing of sending the billing signal by the analog switch is determined by the time when the caller makes a call, and the time at which the billing signal is sent is determined. As shown in FIG. 6B, if it is t1, t2, t3, time t1, t
Instantaneous values at 2 and t3 are output and switched at random times. An analog low-pass filter (CR filter or active filter) 28 using a capacitor and a resistor is used to remove the charging signal output from the analog switch, but the switching time of the analog switch is 0,1 / 2f0. , 1 / f0, 3 /
2, f0, ..., m / 2f0 (seconds) (m is a positive integer)
When the instantaneous value of the signal v2 becomes “0”, the analog low-pass filter 28 outputs the signal shown in FIG.
The signal v3 as shown in (c) is output. This signal v3 adds the amplitude determined by CR to the amplitude in the steady state at the moment when the analog switch is switched by the transient current flowing in the CR of the analog low pass filter 28 or within the time determined by CR. Was done,
There is a problem that the signal amplitude due to the transient response of the low-pass filter 28 becomes noise other than the voice signal and is transmitted to the opposite station side. Further, the amplitude of the signal in this transient state increases as C and R increase, and therefore the steady state is maintained even if the order of the analog low-pass filter 28 using C and R is increased to make the cutoff characteristic steep. Although it is effective to suppress the amplitude of the noise, there is a problem that the noise cannot be reduced beyond a certain value because the amplitude in the transient state cannot be suppressed.

[0008]

In order to solve such a problem, the present invention provides a delay circuit that outputs a signal delayed by a certain time from an input signal, and a waveform that makes the rising and falling waveforms of the delay circuit steep. A timing adjusting circuit including a shaping element and a flip-flop circuit that controls the charging signal in synchronization with the rising or falling time of the signal output from the waveform shaping element is provided.

[0009]

Since the switching time of the charging signal can be arbitrarily set by the timing adjusting circuit, it is possible to prevent the noise generated at the moment when the charging signal is transmitted or stopped from transmitting to the opposite station side.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of a billing signal transmitting circuit according to the present invention, and FIG. 2 is a waveform diagram of each part of the circuit. In FIG. 1, the oscillator circuit 1 repeatedly oscillates at a frequency n times the charging signal frequency f0 (H _Z ) to obtain nf0
A rectangular wave signal having a frequency of (H _Z ) is output. Then this signal is metering signal f0 (H _Z) to 1 / n frequency division in the frequency divider circuit 2. Then, the divided rectangular wave signal f0
Since (H _Z ) is a collective wave of a sine wave signal having this signal f0 (H _Z ) as a fundamental wave and a sine wave signal of an odd multiple thereof, the low pass filter 3 causes 3 f0 (H _Z ) or more. The harmonics are removed and the sine wave signal f0 (H _Z ) is obtained.

The sine wave signal extracted by the low pass filter 3 is a signal extracted with reference to about Va / 2 (V), where the amplitude of the output signal of the frequency dividing circuit 2 is Va (V). Therefore, the DC component is removed by the capacitor 4, and the sine wave signal v shown in FIG.
1 is obtained. The sine wave signal v1 is sent to the analog switch 5, the control terminal 11 for controlling the switching of the analog switch is connected to the Q terminal or the Q inversion terminal of the flip-flop 9, and the Q terminal or the Q inversion terminal of the flip-flop 9 is connected. The output signal v1 of the low-pass filter 3 is transmitted to the 2W-4W conversion circuit 14 depending on whether the output logical value of 1 is "1" or "0".

The output of the delay circuit 7 composed of a capacitor and a resistor is connected to the CK terminal of the flip-flop 9 via a waveform shaping element 8, and the frequency divider 2 is connected to the input of the delay circuit 7. The output of is connected. Here, when the output signal of the frequency dividing circuit 2 is applied to the delay circuit 7, the output v2 of the waveform shaping element 8 is the CR in the delay circuit 7.
Then, the output time of the frequency dividing circuit 2 is delayed by the time determined by the threshold value of the waveform shaping element 8 and the waveform becomes as shown in FIG.

The delay time Td obtained by comparing the output signal v2 of the waveform shaping element 8 with the output signal of the frequency dividing circuit 2 is a value (-180 ° ×) in which the phase delay of the low pass filter 3 can be ignored.
m; where m is “0” or a positive integer), the output amplitude of the frequency dividing circuit 2 is Va, and the threshold value of the waveform shaping element 8 is Vt.
If h, it is determined by the equation (1). That is,

Td = CR · ln (1-Vth / Va) ... (1)

During the time Td determined by the above equation (1),
Even if the logical value of the charging signal control terminal 11 is input to the D terminal of the flip-flop 9, the output logical value of the waveform shaping element 8 (that is, the input logical value of the CK terminal of the flip-flop 9) does not change, and thus the charging signal is output. Although not performed, the charge signal is output because the input logical value of the CK terminal changes after the time Td. Therefore, by setting CR of the delay circuit 7, the switching operation can be performed at any time.

On the other hand, the charging signal f0 (H _Z ) is shown in FIG.
As shown in, when random switching is performed within the range of time t = 0 to 1 / 2f0 (seconds), a different signal waveform is output to the output of the analog low pass filter 16 depending on each switching time. .. This change in the signal waveform is due to an increase or decrease of the harmonic component having the frequency f0 (H _Z ) as the fundamental wave, and a graph showing the ratio of the fundamental wave to the harmonic wave is shown in FIG. 3 (b).

As shown in FIG. 3B, 1 / 4f0
If the analog switch 5 is switched at the moment of (seconds), the harmonic component of the charging signal increases, and thus the charging signal frequency component f0 (H _Z ) that is the fundamental wave thereof decreases most. If the period and frequency are the same, if the amplitude is small, that is, if the component of the charging signal frequency f0 (H _Z ) is small, the noise transmitted to the opposite station side is also reduced.

Further, the sending side 4 of the 2W-4W conversion circuit 14
The analog low-pass filter 16 that suppresses the charging signal transmitted from the line terminal to the receiving side 4-wire terminal is attenuated so as to have a constant attenuation amount at the frequency f0 (H _Z ) as shown in FIG. 4B. The characteristic is set. Therefore, even if the output signal of the analog switch includes a harmonic component having a frequency f0 (H _Z ) or higher, the analog low-pass filter 1
6 attenuates the attenuation at the frequency f0 (H _Z ) by several times.

That is, the attenuation amount in the sufficient attenuation range of the analog low pass filter 16 is represented by K × 6 dB / OCT (K is the filter order), and the analog low pass filter 1
If, for example, a fourth-order filter is used for 6, the frequency f0
The amplitude of the second harmonic 2f0 (H _Z) of (H _Z) frequency f
The value is 24 dB lower than that of 0 (H _Z ). Therefore, the harmonic component generated at the moment when the analog switch 5 is switched is ignored as compared with the case of the frequency f0 (H _Z ). Therefore, the frequency f0 (H _Z ) component is decreased by the increase of the harmonic component, and it is low at 1/4 f0 (seconds), and similarly, when the instantaneous value after 1 / f0 (seconds) becomes the maximum positive and negative values. By setting the time of the above formula (1) in consideration of the phase delay of the band pass filter 3, it is possible to suppress the noise accompanying the transmission of the billing signal transmitted to the opposite side.

As described above, in order to reduce the amplitude of the transient response of the analog low pass filter which causes noise, the timing adjusting circuit 15 capable of arbitrarily setting the switching time of the charging signal is used. By setting the sending time to the time when the charging signal frequency component decreases the most, that is, the time when the charging signal amplitude is the smallest, the noise generated at the moment of sending or stopping the charging signal is prevented from being transmitted to the opposite station side. To be done.

[0021]

As described above, according to the present invention,
Since the switching time of the charging signal can be arbitrarily set by the timing adjusting circuit, it is possible to prevent the noise generated at the moment of sending or stopping the charging signal from being transmitted to the opposite station side.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a charging signal transmission circuit according to the present invention.

FIG. 2 is a signal waveform diagram of each part of the circuit of the embodiment.

FIG. 3 is a diagram showing a relationship between an analog switch output signal and its frequency component in the circuit of the embodiment.

FIG. 4 is an input / output characteristic diagram of an analog low pass filter in the circuit of the embodiment.

FIG. 5 is a block diagram of a conventional billing signal transmission circuit.

FIG. 6 is a signal waveform diagram of each part of the conventional circuit.

[Explanation of symbols]

 1 Oscillation circuit 2 Dividing circuit 3 Low-pass filter 4 Capacitor 5 Analog switch 7 Delay circuit 8 Waveform shaping element 9 Flip-flop 11 Billing signal control terminal 12 Billing signal output terminal 13 2-wire subscriber connection terminal 14 2W-4W conversion Circuit 15 Timing adjustment circuit 16 Analog low pass filter

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yutaka Terasaki 5-7-1, Shiba, Minato-ku, Tokyo NEC Corporation

Claims (1)

[Claims] 1. An analog voice signal from a public telephone connected to a two-line subscriber line is PCM coded, and
A billing signal sending circuit that is housed in a PCM terminal device that converts a PCM-coded digital signal into an analog signal and sends a billing signal to the public telephone outputs a rectangular wave signal having a frequency several times that of the billing signal. An oscillator circuit, a divider circuit that outputs a rectangular wave signal that is obtained by dividing the output signal of the oscillator circuit to an arbitrary billing signal frequency, a low-pass filter that extracts a sine wave signal from the output signal of the divider circuit, and a low-pass filter. A billing signal transmission circuit comprising an analog switch for controlling transmission of an output signal of a bandpass filter and a timing adjustment circuit for arbitrarily setting a switching time of the analog switch.