JPS5831140B2 - signal receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal receiver that receives push button signals and the like.

When signals are transmitted using the so-called END-TO-END method in which data is transmitted from subscriber terminals to a central data receiving device using pushbutton signals, echoes may occur due to the 4-wire loop at the relay stage (Reference Literature IEEE
TRANSACTIONS COMMUNICAT
ION TECHNOLOGYVOL, C0M-15
, NO, 6, DEC67' P P812-824)
.

Therefore, a multi-frequency signal receiver that receives these data requires protection means to prevent it from being affected by echoes.

Conventionally, as this protection means, (1) AGC circuit (the above-mentioned document) and (2) pad control circuit (Japanese Patent Publication No. 49-15643, etc.) have been known, but in (1), the AGC circuit is relatively complicated. be.

(2) requires a relay circuit and an external reset signal for pad control.

It had the following drawbacks.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal receiver that eliminates the drawbacks of the prior art described above and achieves the same function with a simpler circuit.

The present invention provides the echo protection means by providing a maximum value detection circuit that detects the maximum value of the input signal and a variable threshold circuit that varies the detection level of the limiter circuit according to the sono output level. The present invention will be described below in accordance with detailed specific embodiments.

FIG. 1 shows a conventional example using an AGC circuit.

The multi-frequency signal input to the input terminal IN is made into a constant level by the AGC circuit 1, and then divided into high groups,
Each wave is separated into low groups.

Thereafter, it is input to the limiter circuits 3' and 3'', and only those above a preset level enter the channel filter 4 as a rectangular output, and it is determined by the level detection circuit 5 whether or not the frequency is to be detected. The subsequent output circuit 6 checks whether to output or not, and outputs 0UT1.
An output is generated at the corresponding terminal of ~8.

Here, the AGC circuit 1 is activated by the dominant level that reaches the receiver first, and the echo component that arrives subsequently (which is always lower than the level that arrives first, typically 14 to L5 dB).
The falling response time of the AGC circuit is the time at which the echo component arrives (usually at a maximum of 40 ms).
By setting the opening operation of
Prevents the influence of echoes.

However, the structure of an AGC circuit is generally complicated and expensive.

1.Although not shown, when using the other method, a "pad control circuit," the relay for inserting and removing the pads, the circuit for controlling the pads, and the inserted pads must be removed. Since a reset signal and the like are required for this purpose, the configuration is complicated and large, and there are drawbacks in terms of reliability.

The method according to the present invention shown in FIG. 2 overcomes these drawbacks.

In Fig. 2, the input multi-frequency signal is separated into one high group wave and one low group wave by a wave splitter 2, and then applied to limiter circuits 3' and 3''. At the same time, the voltage is also applied to the maximum value detection circuits 7' and 7''.

The maximum value of one component of the input signal detected here is then input to the variable threshold circuits 8', 8'', where it is compared with the lowest level (fixed threshold) VF (see FIG. 4) to be received; First, it is checked whether the level is to be detected or not, and if the level is to be detected, the threshold value is attenuated by the necessary amount (usually 2 to 3 dB is sufficient7) than the previously detected maximum value, and then the limiter 3' , 3" to the detection level generation terminal 9 (see Fig. 4), and if it is not at the level to be detected, the fixed threshold value VF is applied.
Apply.

On the other hand, since one wave of the input signal from the splitter filter 2 has arrived at the other end of the limiter circuits 3', 3'', the level applied to both terminals of the limiter circuits 3', 3'' is is compared, and only when it exceeds the level applied to the detection level generation terminal, a rectangle is output from the limiter circuit, and thereafter the signal is processed in the same procedure as explained in FIG.

Here, when an echo component arrives, by appropriately setting the discharge time constant of the maximum value detection circuits 1' and 7" (about 40m5 like the AGC circuit), the limiter circuit 3', 3" operation can be prevented.

The maximum value detection circuits 7', 7'' and the variable threshold circuit 8 described above
3' and 8'' are shown in FIGS. 3 and 4, respectively.

First, in the maximum value detection circuit shown in FIG. 3, the maximum value of the manually input signal is charged and stored in the capacitor C1.

Further, this maximum value is maintained at a level higher than the level due to the echo component for a time determined by the time constant C1·(R1+R2).

At the same time, the maximum value is attenuated by a ratio determined by R2/(R1+R2) and applied to the subsequent variable threshold circuits 8', 8''.

On the other hand, the variable threshold circuit shown in FIG.
C2 and a diode D2, the output level PHIN from the maximum value detection circuit is compared with the fixed threshold value VF, and the dominant level is detected at the level generation terminal 9.
Output to.

The level of this terminal 9 is compared with one component applied from IN' separated by the splitter filter 2, and the limiter circuit 3 outputs only the level exceeding the terminal 9 as a rectangular signal.

Among the above, instead of providing a maximum value detection circuit and a variable threshold circuit for each output of the high group and low group, it is possible to provide one circuit for each in common, and to receive single-frequency reception that does not require a p/p divider. Needless to say, the method can also be applied to vessels.

As described above, the signal receiver according to the present invention has a simple circuit configuration and can economically realize a protection means that is not affected by echoes.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one example of the prior art, FIG. 2 is a block diagram showing one embodiment of a signal receiver according to the present invention, and FIGS. 3 and 4 are circuit configurations for realizing the present invention. For example,
FIG. 3 is a circuit diagram showing a maximum value detection circuit, and FIG. 4 is a circuit diagram showing a variable threshold circuit and a limiter circuit. 2...P-wavelength divider, 3', 3"...Limiter circuit, 4...Channel filter, 5.
...Level detection circuit, 6...Output circuit,
7', 7"...Maximum value detection circuit, 8', 8"...
...Variable threshold circuit, 9...Detection level generation terminal, 10...Fixed threshold power supply, IC3+2,
3...Op amp.

Claims (1)

[Claims] 1. A limiter circuit that operates according to the signal level of a human input signal, a bandpass filter that passes the output of the limiter circuit in a predetermined frequency band, and a bandpass filter that operates when the output level exceeds a predetermined level. A signal receiver composed of a level detection circuit includes a maximum value detection circuit that detects the maximum value of the input signal and holds an output level corresponding to the detected value for a predetermined period of time, and A signal receiver comprising: a variable threshold circuit that compares the threshold value with a fixed threshold value and sets the dominant level as the detection level of the limiter circuit.