JPH03195170A - signal receiving circuit - Google Patents

Abstract

PURPOSE:To obtain a signal reception circuit to satisfy an applied standard by applying a second voltage level lower than a first voltage level to a comparator and afterwards deciding an input signal to be received by the second voltage level when the signal more than the first voltage level is detected as the input signal. CONSTITUTION:A comparator 1 is provided to compare the input signal with the prescribed voltage level, and a threshold value changing means 2 is provided to change the prescribed voltage level to be applied to the comparator 1. When the signal more than the level of a first voltage V2 is detected in respect to the input signal, the level of a second voltage V1 lower than the level of the first voltage V2 is applied to the comparator 1 by the threshold value changing means 2, and afterwards, the input signal to be received is decided by the level of the second voltage V1. Thus, the signal reception circuit can be obtained to always satisfy the applied standard.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to provide a signal receiving circuit that satisfies a given standard regarding a signal receiving circuit that receives an alternating current signal whose frequency is constant and whose amplitude value fluctuates. a comparator for comparing the predetermined voltage level with a voltage level, and a threshold value changing means for changing the predetermined voltage level applied to the comparator, and when a signal of a first voltage level or higher is detected with respect to the input signal, the threshold value is changed. A second voltage level smaller than the first voltage level is applied to the comparator by means of the comparator, and input signals received thereafter are determined at the second voltage level.

[Industrial Application Field] The present invention relates to a signal receiving circuit for a private branch exchange (hereinafter referred to as PBX) that receives billing signals from a central office exchange, and in particular receives an alternating current signal whose frequency is constant and whose amplitude value varies. This invention relates to a signal receiving circuit.

FIG. 4 is a block diagram of an example of a communication system to which the present invention is applied, and a diagram showing standards of a signal receiving circuit.

In FIG. 4(A), while the PBX is communicating via the central office exchange 10, a sinusoidal billing signal is sent from the central office exchange 10, and the signal receiving circuit 21 of the PBX II receives this.

As standards for this signal receiving circuit 21, there are the following standards depending on the country.

It is assumed that the output level of the billing signal oscillator of the central office exchange 10 fluctuates, for example, by about 5%, and as shown in FIG. 4(B).
, voltage ■1 close to the noise level and voltage ■2 slightly higher than the level fluctuation width of the billing signal than voltage ■1 are determined, and as shown in Fig. 4 (
As shown in (e) of Fig. 4 (B), when the maximum value of the input signal peak is less than the voltage ■1, no signal is received, and (d) of Fig. 4 (B)
) (C) As shown in (b), among the peak values of the input signal,
If there is anything between voltages ■1 and ■2, it will output a signal with the same frequency as the input signal or will not receive it, as shown in Figure 4 (B).
As shown in (a), the minimum value of the peak of the input signal is at voltage 7.
When it is 2 or more, a signal with the same frequency as the input signal must be output.

Therefore, a signal receiving circuit that meets the above standards is required.

Note that the voltages Vl and V2 hereinafter refer to the voltages defined above.

[Conventional technology]

FIG. 5 is a block diagram of a conventional signal receiving circuit and a time chart of input signals and output signals.

The signal receiving circuit of FIG. 5(A) uses a comparator 1, and a sine wave whose peak value fluctuates by, for example, 5% and whose frequency is approximately constant is input to one terminal, and a resistor R6 is input to the other terminal. , R7 divides the voltage V to give a threshold voltage V, and voltage ■ is applied to the output via the resistor R5. When the input signal exceeds the threshold voltage Vth, the output goes to O level, the threshold. If the voltage is less than V, it becomes a level.

In this signal receiving circuit, if the threshold voltage V is the voltage ■l, then (a), (b) (
In the case of c), a signal with the same frequency as the input signal is output, and (
In case e), it is not received, but in case (d), some of the peak values exceed the threshold voltage V, so the output is a signal with a frequency different from the input signal, and this case does not comply with the standard. Not satisfied.

Also, if the threshold voltage v th is the voltage ■2, then Fig. 5 (B)
In case (a), output a signal with the same frequency as the input signal,
In cases (c), (d), and (e) of Fig. 5 (B), no reception is received, but in case (b), some peak values exceed the threshold voltage v th, so the output is The signal will have a frequency different from that of the input signal, and in this case the standard will not be met.

In addition, as shown in FIG. 5(B), the threshold voltage v th is
1 and ■2, in the case of (a) and (b) in Fig. 5(B), a signal with the same frequency as the input signal is output, and in the case of (d) and (e) in Fig. 5(B) In the case of (C), the signal is not received, but in the case of (C), some of the peak values exceed the threshold voltage V, so the output is a signal with a frequency different from the input signal, and this case does not satisfy the standard. .

In the conventional signal receiving circuit, no matter where the threshold voltage v th is selected, any of the four conditions shown in FIG. 5(B) (a) to (e) is not satisfied.

[Problem to be solved by the invention]

As explained above, there is a problem that conventional signal receiving circuits do not meet the given standards.

The present invention aims to provide a signal receiving circuit that satisfies given standards.

[Means to solve the problem]

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

In a signal receiving circuit that receives an alternating current signal whose frequency is constant and whose amplitude value varies, as shown in FIG. A threshold changing means 2 is provided for changing the level, and when a signal higher than the level of the first voltage v2 is detected with respect to the input signal, the threshold changing means 2 controls the input signal to be lower than the level of the first voltage v2. The level of the second voltage (1) is applied to the comparator 1, and the input signal to be received thereafter is applied to the second voltage.
The configuration is such that the determination is made at the level of the voltage (1).

[For production]

According to the present invention, since the normal threshold voltage of the comparator 1 is 2, the maximum value of the peak of the input signal is the voltage as shown in (c), (d), and (e) of FIG. ■When the voltage is 2 or less, no reception is received, and as shown in Figure 4 (B) (a), when the minimum value of the peak of the input signal is 72 or more, a signal with the same frequency as the input signal is output. do.

As shown in (b) of Figure 4 (B), if the maximum value of the peak is voltage 72 or more, and the minimum value is voltage 2 or less and voltage 1 or more, the peak value of the input signal exceeds voltage v2. At this point, the threshold voltage becomes 1, so a signal with the same frequency as the input signal is output.

In other words, it satisfies all the given standards.

[Embodiment] FIG. 2 is a block diagram of a signal receiving circuit according to an embodiment of the present invention.
FIG. 3 is a time chart of each part in FIG. 2, where (A) is an input signal and (B) is an output signal.

(C) shows the output of the monostable multi-by-break 3, and (D) shows the output of the NOT circuit 4.

The switch SW in FIG. 2 is normally on the solid line side, and the voltage ■ is divided by resistors R1 and R2 to give voltage ■2 as the threshold voltage of the comparator 1. When the switch SW is on the dotted line side, the resistor R3
is connected in parallel with the resistor R2, so that the threshold voltage becomes voltage ■1.

Therefore, as shown in (c), (d), and (e) of FIG. 4(B), if the maximum value of the peak of the input signal is less than the voltage 2, no signal is received. As shown in (a) of Figure 4 (B),
If the minimum value of the peak of the input signal is also voltage 72 or higher, then a signal with the same frequency as the input signal is output.

Next, the case shown in FIG. 4(B)(b) will be explained using FIGS. 2 and 3.

As shown in Figure 3 (A), the peak of the input signal is at voltage V2.
When the value exceeds 0, the output becomes 0 level, as shown in FIG. 3(B), and the monostable multi-by-break 3 is activated.

Then, during a width larger than one cycle of the input signal as shown in Figure 3 t, which is determined by the time constant of resistor R4 and capacitor C, the output of monostable multi-bi break 3 is at the 0 level as shown in (C). Therefore, the output of the knot circuit 4 becomes a level as shown in FIG. 3(D), and the switch SW is set to the dotted line side.

Then, the threshold voltage becomes voltage ■1.

In this case, all the peaks of the input signal exceed the threshold voltage v1, and each time the peak of the input signal exceeds the threshold voltage v1, the output of the comparator 1 becomes O level, the monostable multi-vibration break 3 is activated, and the output remains at the 0 level as shown in (C). The output of the knot circuit 4 is on the side of the rubel as shown in (D), and the switch SW is on the side of the dotted line.
As shown in (B), a signal having the same frequency as the input signal is output from the output.

Note that when the input signal is disconnected, the switch SW changes to the solid line side and returns to its original state.

As shown in (a) of FIG. 4(B), if the minimum value of the peak of the input signal is also higher than the voltage v2, the peak of the input signal is at the voltage
If it exceeds 2, the threshold voltage becomes voltage 1 as described above, so of course a signal having the same frequency as the input signal is output.

That is, the signal receiving circuit shown in FIG. 2 satisfies all standards.

Although the input signal has been described as a sine wave, it goes without saying that even a rectangular wave or a triangular wave satisfies all standards.

〔Effect of the invention〕

As explained in detail above, according to the present invention, it is possible to obtain a signal receiving circuit that satisfies the given standards.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram of a signal receiving circuit according to an embodiment of the present invention, Fig. 3 is a time chart of each part of Fig. 2, and Fig. 4 is an example of the present invention. FIG. 5 is a block diagram of a conventional signal receiving circuit and a time chart of input signals and output signals. In the figure, ■ is a comparator, 2 is a threshold value changing means, 3 is a monostable multivib break, 4 is a knot circuit, 10 is a central office exchange, 11 is a private branch exchange, 21 is a signal receiving circuit, R1-R7 are resistors, and C is a Capacitor, open rod 220 Kichikuo 9, Butsuko yard 13, record of the number of guests of the sun and moon, receiving the title of a priest, Zhandan 10,000 &'s mouth 7f 2j
2 Figure (a) (C) Cd') (e) 485-

Claims (1)

[Claims] A signal receiving circuit that receives an alternating current signal having a constant frequency and varying amplitude values, comprising: a comparator (1) that compares an input signal with a predetermined voltage level; and a voltage applied to the comparator (1). A threshold changing means (2) for changing the predetermined voltage level is provided, and when a signal of a first voltage level or higher is detected for the input signal, the threshold changing means (2) changes the first voltage level to the first voltage level. A smaller second voltage level is applied to the comparator (1).
), and determines an input signal to be received thereafter at the second voltage level.