JPS6234307B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that bidirectionally transmits a control tone signal on a single line, and in particular, the influence of the outgoing signal on the incoming signal when the incoming signal level is significantly lower than the outgoing level. Regarding the reduction of

When a control tone signal is transmitted bidirectionally using a single line with a large transmission loss, problems such as masking of an incoming signal by an outgoing signal, cross modulation, and crosstalk occur. For example, as shown in Fig. 1, when transmitting and receiving devices A and B are connected by a telephone line LINE and a 3KHz control tone signal is transmitted in both directions, the tone signal output level from device A is -
If it is specified as 26 dBm and the line loss is 35 dB, the incoming signal level at device B will be -61 dBm. In contrast, the output level from device B is 0 dBm.
If this were allowed, the difference in transmission and reception levels at device B would be as much as 61 dB. If the incoming signal level is -61 dBm, it cannot be processed, so it is amplified. However, the amplifier used at this time generally has a characteristic that the outgoing signal is mixed in, so if left as is, the amplifier will become saturated and the receiving system will malfunction. To avoid this, it is necessary to use a hybrid circuit, a high selectivity filter, or an amplifier with a wide dynamic range.

Figure 2 shows a transformer type hybrid on the device B side.
An example using HYB, going up from the track LINE (A→
B) Tone signal (incoming signal) TU is transformer
It is led to an amplifier (not shown) through the TR, attenuator ATT, and hybrid HYB. On the other hand, the downstream (B→A) tone signal (transmission signal) TD is transmitted to the line LINE through the hybrid HYB, attenuator ATT, and transformer TR. Hybrid HYB
One end of the primary side _T1 is connected to the line LINE side, and the other end is connected to the dummy impedance DMY. When the signal TD is injected into the intermediate tap of the primary side _T1 , if the symmetry is maintained and the impedances at both ends are equal, no output signal component will appear on the secondary side _T2 . Moreover, the incoming signal
The TU is delivered with a loss of 1-2 dB in the hybrid HYB. However, it is extremely difficult to realize such ideal hybrid separation characteristics in an actual line, and generally the secondary side T ₂ It is unavoidable that some of the transmitted signal TD will leak during the transmission. The attenuator ATT is designed to minimize the effects of impedance on the line LINE side, even if it is unknown or fluctuates. However, in order for the attenuator ATT to be fully effective, its attenuation amount is often around 20 dB, which further reduces the level of the incoming signal TU, and the signal-to-noise ratio (S/N) of the amplifier that amplifies it. becomes a problem. Furthermore, even if the output signal TD is used, it is necessary to increase the attenuation by the attenuation due to the hybrid input, so it is not a good idea to use an attenuator.

The present invention attempts to effectively eliminate interference caused by transmitted signals without requiring high performance from hybrids or filters, and without using an attenuator.The present invention has the following characteristics:
In a control tone signal transmission circuit that bidirectionally transmits a control tone signal on a line, a circuit that bursts the outgoing signal and a decoder for the incoming signal are inactivated during the mark period of the bursted outgoing signal. , and a circuit that is activated only during a space period, and the decoder has a circuit that maintains an intermittent output signal for a certain period of time. below,
This will be explained in detail with reference to the illustrated embodiment.

FIG. 3 is a block diagram showing one embodiment of the present invention. Railway line, transformer TR, hybrid
The relationship between HYB and attenuator is as shown in Figure 2.
ATT is omitted. Incoming calls are AMP ₁ , 2900
±100Hz bandpass filter BPF ₁ , amplifier
AMP ₂ and a decoder DEC, which includes mechanical filters MF ₁ to MF ₃ with resonance frequencies of 2850 Hz, 2900 Hz, and 2950 Hz, and rectifying and smoothing circuits REC ₁ to _{REC 3} connected to their subsequent stages. This is because in this example, it is assumed that the uplink tone signals TU ₁ , TU ₂ , and TU ₃ are 2850 Hz, 2900 Hz, and 2950 Hz, respectively, and when one or more of these is received through the line LINE, the output of the decoder DEC
The corresponding one among OUT ₁ to OUT ₃ is turned on. The transmission system consists of an oscillator OSC ₂ that generates a 3000Hz down tone signal TD ₁ (sine wave) and a 3000Hz bandpass filter BPF ₂ that is used as necessary.

The circuit added by the present invention is inside the broken line.
SW _R is the hybrid HYB (secondary side T ₂ ) and amplifier
Analog switch for the incoming signal interposed between AMP ₁ , SW _T is the oscillator OSC ₂ and the hybrid HYB
The analog switch for sending signals, OSC ₁ , which is interposed between the primary side T ₁ of
The oscillator that generates a, INV, is an inverter that inverts the rectangular wave a. In this example, the output a of the oscillator OSC ₁
The switch SW _T is directly turned on and off by the inverter INV, and the switch SW _R is turned on and off by the inverted signal from the inverter INV, but this relationship may be reversed. switch
When SW _T is turned on and off with a square wave a, the oscillator OSC ₂
The output of is bursted. FIG. 4 shows this waveform, and b is the waveform of the bursted transmission signal _TD1 at the switch SW _T. switch
Since _SWR is off during the mark period M of waveform b, the output of the hybrid HYB is not input to the decoder DEC during this period. That is, the decoder DEC
is in an inactive state where none of the outputs OUT ₁ to _{OUT 3} can be turned on. Therefore, even if part of the transmitted signal leaks to the receiving system through the hybrid HYB during this period M, the decoder DEC will not malfunction. On the other hand, the space period S of waveform b is
When _SWR is turned on, the decoder DEC is activated, and outputs OUT ₁ to _{OUT 3} are generated therefrom according to the incoming signal. However, since the switch SW _T is off, there is no possibility that part of the output signal will flow through the hybrid HYB to the decoder DEC side during this period.

Note that if device B has this configuration, the decoder
Since the output of the DEC is intermittent, in order to avoid such a situation, the outputs OUT ₁ to UOT ₃ are maintained for a certain period of time using the time constants of the rectifier and smoothing circuits REC ₁ to _{REC 3} . Also, if filter BPF ₂ is used, the sideband of the tone burst signal can be limited, but in this case, the falling part of the output c of filter BPF ₂ has a tail as shown in Figure 4, so as shown in Figure 5. Diode D ₁ , resistance R ₁ , capacitance in front of inverter INV
A delay circuit DLY is provided to delay the fall of the signal a consisting of _C1 by a time τ. The delay circuit DLY then generates a signal d at the output of the inverter INV, which turns off the switch SW _R until the fall of the signal c is almost completed.

As described above, according to the present invention, it is a circuit that bidirectionally transmits control tone signals by sharing one line, and does not require high performance from the hybrids, filters, etc. used, and does not require an attenuator. There is an advantage in that the negative influence of the transmitted signal on the incoming signal can be significantly reduced by a simple circuit configuration that does not require any interference. Further, as long as the tone signal is being sent out, the output of the decoder will not be interrupted, so there will be no problem with control.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a bidirectional transmission system for control tone signals, Fig. 2 is an explanatory diagram of a transformer type hybrid, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a diagram of each part signal. The waveform diagram and FIG. 5 are main part block diagrams showing a modification of the present invention. In the figure, LINE is a line, DEC is a decoder, SW _R is an analog switch for incoming signals, SW _T is an analog switch for sending signals, OSC ₁ is a square wave oscillator for switching switches, and INV is an inverter.

Claims (1)

[Claims] 1. In a control tone signal transmission circuit that bidirectionally transmits a control tone signal over a single line, the circuit that bursts the outgoing signal and the decoder for the incoming signal are connected to each other during the mark period of the bursted outgoing signal. and a circuit that is activated only during a space period, and the decoder has a circuit that maintains an intermittent output signal for a certain period of time.