JPH02260790A - Detection circuit for one frequency signal in voice frequency band - Google Patents

Abstract

PURPOSE:To prevent a malfunction due to a large input level or impulse noise by providing a phase discrimination detection means adding the outputs of 1st and 2nd filters to discriminate the phase and a comparison means comparing the output of the phase discrimination means with a reference value. CONSTITUTION:Phase discrimination detection means 16-19 add the outputs of 1st and 2nd filters 12, 15 to discriminate the phase. Comparing means 20-22 compare the outputs of the phase discrimination detection means 16-19 with a reference value and generate, e.g. a low level when the former is larger than the latter to discriminate the presence of one frequency signal, that is, an in- band signal and generate, e.g. a high level when the former is smaller than the latter to discriminate the absence of one frequency signal. Thus, the malfunction due to voice, music tone or noise or the like is surely prevented and the in-band signal detected without being affected by a large input signal and impulse noise.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention uses a frequency signal detection circuit within the voice frequency band, particularly a single frequency signal within the voice band, and detects a dial signal or a supervisory signal depending on the presence or absence of the signal. The present invention relates to an in-band signal detection circuit in an audio band-frequency signal system for transmitting.

[Summary of the invention]

The present invention provides a signal detection circuit for an audio frequency signal system that transmits a dial signal using an audio frequency signal using an audio frequency signal. a second filter that blocks only the signal; an analog switch provided after the second filter that cuts off the output of the second filter when there is no call and connects it when there is no -frequency signal; By providing a phase determination detection means that performs phase determination by adding the outputs of the two filters, and a comparison means that compares the output of this phase determination detection means with a reference value, it is possible to prevent malfunctions caused by large input levels or impulsive noise. The present invention is designed to prevent this, improve reliability, simplify the circuit configuration, and reduce costs.

[Conventional technology]

In general, it is important that signal detection circuits in the audio band-frequency signal system do not malfunction due to human input voice, musical tones, noise, and the like.

Figure 6 shows an example of a conventional in-band signal detection circuit, in which the frequency of the in-band signal from the input terminal (1) is filtered by a band pass filter (BPF) (2) and rectified.
The signal is supplied to a smoothing circuit (3), where it is rectified and smoothed, and then supplied to one input side of a comparison circuit (4).

In addition, a band elimination filter (BEF) (5) that blocks the frequency of the in-band signal detects voice, musical tone, and noise components other than the frequency of the in-band signal from the input terminal (1), and rectifies and rectifies the detected output. The signal is supplied to the smoothing circuit (6), where it is rectified and smoothed, and then supplied to the other input side of the comparison circuit (4). The comparison circuit (4) compares both input signals and determines the presence or absence of an in-band signal.

Normally, the rectifier/smoothing circuit (6) side has a higher gain than the rectifier/smoothing circuit (3) side, and this is generally called the guard ratio, which is set to a higher value with various values such as 8 dB, 12 dB, and 16 dB. ing.

When an in-band signal is supplied from the input terminal (1), the level at one input side of the comparator circuit (4) is higher than the other input side, indicating that there is an in-band signal at its output side, e.g. Outputs a low level signal. On the other hand, when an in-band signal is not supplied from the input terminal (1) (no call) or when a voice signal etc. is supplied (during a call), the level of the negative input side of the comparator circuit (4) is the same as that of the other side. It outputs, for example, a high level signal indicating that there is no in-band signal on the output side.

[Problem to be solved by the invention]

However, in the case of the conventional circuit shown in Fig. 6, the signal detection side, that is, the bandpass filter (2), the rectification/smoothing circuit (3)
side and the detection side other than the signal (guard side), that is, the bandpass filter (5), rectification/smoothing circuit (6) side, respectively.
Since the voltages are compared after smoothing, if a large level of human power is applied or impulsive noise is input, the circuit may become saturated and the power of both comparators (4) may become the same, resulting in malfunction. .

Furthermore, since a filter with relatively steep characteristics is used as the bandpass filter (2), it is expensive, and moreover, the rectifier/smoothing circuit (3) and (6) often use discrete components such as resistors, capacitors, and diodes. This has disadvantages such as the circuit being complicated and expensive.

This invention was made in view of these points, and it eliminates the drawbacks of the conventional technology, prevents malfunctions caused by large input levels and impulsive noise, has higher reliability, and is economical by simplifying the filter and reducing the number of parts. The present invention provides a typical audio frequency band-frequency signal detection circuit.

[Means to solve the problem]

This invention provides a first filter (15) that passes a high frequency band of the audio frequency band in a signal detection circuit of an audio band-frequency signal method that transmits a dial signal using an audio frequency signal of the audio frequency band. , a second filter (12) that blocks only -frequency signals, and a second filter (12) that blocks only -frequency signals;
A second filter (12) is provided after the second filter (12) when there is no call.
) and an analog switch (13) that turns off the output of the -frequency signal and connects it when there is no -frequency signal, and the first and second filters (12).
, 15) for determining the phase by adding the outputs of the phase determination detecting means (16 to 19);
Comparison means (20 to 19) for comparing the output of 6 to 19) with the reference value
22).

[Operation] The first filter (15) filters the audio frequency band, for example, 0.3
The high frequency band from kHz to 3.4kHz is passed. The second filter (12) blocks only -frequency signals, that is, in-band signals. Analog switch (13)
When there is no call, the output of the second filter (12) is cut off, and -
Closed when there is no frequency signal, that is, when the in-band signal is disconnected. The phase determination detection means (16 to 19) performs phase determination by adding the outputs of the first and second filters (12, 15>).The comparison means (20 to 22) performs phase determination by adding the outputs of the first and second filters (12, 15>). The output is compared with the reference value, and if the former is larger than the latter, it is determined that a one-frequency signal, that is, an in-band signal is present, by generating a low level, and if the former is smaller than the latter, a high level is generated, for example. It is determined that there is no one-frequency signal.This makes it possible to reliably prevent malfunctions caused by voices, musical sounds, noise, etc., and to detect in-band signals without being affected by large human input signals or impulsive noise. can.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on FIGS. 1 to 5. FIG. 1 schematically shows the circuit configuration of this embodiment. In the figure, (11) is an input terminal; (11) is an input terminal;
12) is a BEF that blocks the frequency of the in-band signal, (
13> is an analog switch, (14), (15)
is bypass filter (HP F), (16) is HP
A phase inversion circuit that inverts the phase of the output of F (15), (
17) is the output of HP F (14) and the phase inversion circuit (1
(18) is an analog switch, (19) is a zero cross comparator that detects the zero cross of HP F (15), and the output of this zero cross comparator (19) is It is supplied as a control signal to an analog switch (18). In addition, (16) ~
(19) constitutes a phase determination signal detection circuit.

(20) is a smoothing circuit, (21) is a voltage comparator that compares the output of the smoothing circuit (20) and a reference value (Ref), (22)
) is a delay circuit that delays the output of the comparator (21) for a predetermined time and supplies it as a control signal to the analog switch (13);
(23) is an output terminal.

FIG. 2 is an example specifically showing the circuit configuration of this embodiment. In the figure, parts corresponding to those in FIG. 1 are given the same reference numerals and will be explained. In Figure 2, the input terminal (11)
is connected to the analog switch (1) via B E F (12)
3), and the output side of the analog switch (13) is connected to the HP F (14) and the analog adder (17).
) through the resistor (17a) to the adder (17d)
is connected to the inverting input terminal of

Further, the input terminal (11) is connected to the inverting input terminal of the amplifier (16b) via the HP F 05) and the resistor (16a) of the phase inverting circuit (16). Amplifier(
The non-inverting input terminal of 16b) is grounded. Amplifier(
A resistor (16b) is connected between the inverting input terminal and the output terminal of
6c) is connected. The output terminal of the amplifier (16b) is connected to the adder (17d) via the resistor (17b).
is connected to the inverting input terminal of Adder (17d)
The non-inverting input terminal of is grounded, and a resistor (17c) is connected between the inverting input terminal and the output terminal.

The adder (17d) is connected to the resistors (17a) and (17c).
), (17b) and (17c), the amplification degree on the output side of HP F (14) is 8 to 16 dB.
It is set to be high.

In other words, a guard ratio is set.

The output side of the adder (17d) is an analog switch (1
The output side of the analog switch (18) is connected to the inverting input terminal of the voltage comparator (21) via the resistor (20a) of the smoothing circuit (20).

Further, a smoothing capacitor <20b) is connected between the inverting input terminal of the voltage comparator (21) and the ground. The reference voltage E is applied to the non-inverting input terminal of the voltage comparator (21).
.

is given.

The output side of the voltage comparator (21) is connected to the output terminal (23) and the resistor (22a) of the delay circuit (22).
The reference voltage E2 is connected to the non-inverting input terminal of the amplifier (22b) through the amplifier (22b). Also, resistor (22a)
A diode (22C) is connected in parallel with the amplifier (22b), and a capacitor (22d) is connected between the non-inverting input terminal of the amplifier (22b) and ground. And the amplifier (22b
) output as a control signal to the analog switch (13
).

The output side of HP F (15) is a zero cross comparator (
19), its inverting input terminal is grounded, and its output is supplied as a control signal to the analog switch (18).

Next, the operation of the circuit shown in FIG. 2 will be explained with reference to FIGS. 3 to 5.

First, the case where an in-band signal is input will be explained with reference to FIG. When an in-band signal SI as shown in FIG. 3A is supplied from the input terminal (11), B E
Since it is blocked by F (12), a signal S2 (zero volts) as shown in FIG. 3B is obtained at the output side of the HPF filter 14). On the other hand, the in-band signal SI is HP F (15
), and the phase is inverted by the phase inverting circuit (16), so that a signal S3 as shown in FIG. 3C is obtained on the output side. At this time, the analog switch (13) is connected to the voltage comparator (2).
It is opened by the output of 1).

The signal S, whose phase has been inverted by the phase inversion circuit (16), is supplied to the analog adder (17) and added to the output signal S2 of HP F (14), but in this case, the output signal S2 is B E F ( 12) and the analog switch (13), so that the signal S from the phase inverting circuit (16) is substantially zero volts.
) is amplified and output, and a signal S4 as shown in the third diagram is obtained on the output side.

The signal S4 from the analog adder (17) passes through the HPF (1
The output of 5) is zero-crossed by the zero-cross comparator (19), and the signal S (Fig. 3E) is passed through for the time period when the analog switch (18) is closed, and only the positive terminal is shown in Fig. 3F. It is extracted as a signal S6 like this. This signal S6 is smoothed by a smoothing circuit (20) and the third
The signal S7 as shown in Figure G is generated, and the voltage comparator (21
) and is compared with its reference voltage E1. As a result, a low level (OV) output signal S8 is obtained and held at the output side of the voltage comparator (21), for example, as shown in FIG. 3H. Moreover, this signal S is a delay circuit (2
2), resulting in a signal S as shown in FIG.
3) to hold it open.

Furthermore, when the in-band signal from the input terminal (11) is disconnected, no signal is input to the analog adder (17), and its output becomes zero potential. Therefore the voltage comparator (21)
The potential of the inverting input terminal of is also zero potential.

On the other hand, the reference voltage E+ applied to the non-inverting input terminal of the voltage comparator (21) is set slightly higher than zero potential, so the output of the voltage comparator (21) becomes high level and the delay circuit Through (22) the analog switch (13) is closed.

Next, when the in-band signal is interrupted by the dial, the above-mentioned input state and disconnected state of the in-band signal are repeated.
A dial pulse is reproduced at the output of the voltage comparator (21). FIG. 4 shows this state, and shows the signal waveform when the in-band signal is intermittent (during dialing).

In this state, when an input signal S1 such as voice, musical tone, noise, etc. shown in FIG. 5A is input from the input terminal (11),
On the output side of the HP F (14), a signal S2 as shown in FIG. 5 is obtained from which the in-band signal component and the low frequency component are removed. Further, only the low-frequency component is removed from H P F (15), and the phase is inverted by a phase inversion circuit (16), so that a signal S as shown in FIG. 5C is obtained at its output side.

The signals S2 and 83 thus obtained are supplied to an analog adder (17) and added. Here, as mentioned above, the output side amplification degree of HP F (14) is set to be 8 to 15 dB higher depending on the ratio of resistors (17a) and (17c), and (17b) and (17C). , HPF (14) and phase inversion circuit (16), components other than the in-band signal are sent to the adder (17d).
), the analog adder (1
From 7), output of HPF (14) x resistor (17c)
Value of: Output of phase inversion circuit (16) x value of resistor (17c) from the amplification degree based on the ratio of the values of resistor (17a):
With the amplification factor subtracted by the ratio of the values of the resistor (1711), a signal S4 as shown by the solid line in Figure 5 is obtained at the inverted phase on the HP F (14) side. In other words, excluding the disconnection of the in-band signal component, the signal S is equal to the guard ratio.
2 is obtained.

The signal S output from the analog adder (17) is zero-crossed by the zero-cross comparator (19) and becomes the signal SS (
According to Fig. 5E), the analog switch (18) passes only for the time when it is closed, so that the analog switch (18)
A signal S6 as shown in FIG. F is obtained.

At this time, that is, in the case of a component other than the in-band signal component, the output signal S4 of the analog adder (17) and the control signal S of the analog switch (18), which has been zero-crossed by the zero-cross comparator (19), are opposite to each other. Since it is a phase, the fifth
As can be seen from Figure F, only the negative electrode is taken out.

On the other hand, if an in-band signal component is included in voice, musical tone, noise, etc., the in-band signal component is B E F
(12), so it is not output from the HPF (14), and only the in-band signal component is output from the analog adder (17) at the inverted phase of the output of the phase inversion circuit (16). (17C) Value: Resistor (17C)
b) It is output by amplifying and scaling the value. Then, the signal S outputted from the adder 17) passes through only the time when the analog switch (18) is closed, as in the case other than the in-band signal component, but at this time the output signal of the adder (17) Since S4 and the zero-crossed control signal Ss are in the same phase, only the positive polarity is taken out. That is, this is represented by the fact that the portion corresponding to the in-band signal component in FIG. 5F protrudes toward the positive polarity side.

However, even if there is a positive polarity part in the signal S6, in speech, musical tones, noise, etc., only the in-band signal component has a continuous single frequency and is not included for a period of several msec or more. Therefore, the fifth smoothed by the smoothing circuit (20)
The signal S as shown in Figure G, that is, the DC voltage, is held on the negative side and never exceeds the reference voltage E1, and the output signal s8 of the voltage comparator (21) is input as shown in Figure 5H. It is held at a high level in the same way as when the band signal is disconnected.

The signal sll obtained in this way is transmitted to the delay circuit (22
), the same high level signal SR is generated and the analog switch (13) is closed. In this embodiment, an adder (1
7d) Even if the resistors (17a) and (17b) are saturated,
Adder (17d) at the phase of signal S2 by setting
Since the output signal S is outputted and the phase can be determined, malfunctions due to large human power levels and impulsive noises as in the prior art are prevented.

〔Effect of the invention〕

As described above, according to the present invention, malfunctions caused by voices, musical sounds, noise, etc. can be reliably prevented, and in-band signals as in-band frequency signals can be detected without being affected by large input signals or impulsive noise. can do. In addition, there is no need to use a bandpass filter with steep characteristics as in the past, and rectification can essentially be done with an analog switch (18), which simplifies the circuit configuration and reduces costs. Become.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram showing an embodiment of the present invention, Fig. 2 is a connection diagram showing an example of a specific circuit configuration of Fig. 1, and Figs. 3 to 5 are the diagrams shown in Figs. FIG. 6 is a circuit configuration diagram showing an example of a conventional circuit. (12) is a band elimination filter (BEF),
(13), (1B) are analog switches, (14
), (15) is a bypass filter (HP F)
, (16) is a phase inversion circuit, (17) is an analog adder, (19) is a zero cross comparator, (20) is a smoothing circuit, (21) is a voltage comparator, and (22) is a delay circuit. Ov action Tomibon, June B] Figure 3 (S2) Ov action gun chanting concave Figure 4

Claims (1)

[Claims] 1. In a signal detection circuit of an audio band-frequency signal method that transmits a dial signal using an audio frequency signal in the audio frequency band, a first circuit that passes a high frequency band of the audio frequency band; a second filter that blocks only the above-mentioned -frequency signal; and a second filter provided after the second filter, which turns off the output of the above-mentioned second filter when there is no call, and connects when there is no above-mentioned -frequency signal. a phase determination detection means for performing phase determination by adding the outputs of the first and second filters, and a comparison means for comparing the output of the phase determination detection means with a reference value. Audio frequency band-frequency signal detection circuit. 2. The audio frequency band in-frequency signal detection circuit according to claim 1, wherein said phase judgment detection means comprises a phase inversion circuit, a zero cross comparator, an analog adder, and an analog switch.