JPS5936464A - Tone detector - Google Patents

Abstract

PURPOSE:To obtain a tone detecting circuit resistant to noise, by passing an input signal through a BPF the band of which is changed in response to a tone to be detected and discriminating the period after diciding frequency by a factor of N. CONSTITUTION:An input signal is inputted to a filter means 22 from a terminal 21. The filter means 22 eliminates an unnecessary signal to detect a signal in the specific period range and consists of a switched capacitor filter SCF 23 and a programmable counter 24. A digital discriminating circuit 25 is a frequency detecting circuit having a frequency divider and a counter for cycle measurement, issues a detecting signal and transmits a control signal corresponding to the frequency range to be detected to the counter 24. The frequency dividing ratio of the counter 24 is controlled with a control signal sent from the circuit 25 and the counter 24 gives a clock signal having a suitable frequency to an SCF23. The pass band of the SCF23 is changed with the clock signal given.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a digital tone detection device.

[Technical background of the invention and its problems]

As a tone detection device, a device that performs analog processing is known, as shown in FIG. In this case, a signal input from an input terminal 1 is amplified to some extent by an amplifier 2, and then passed through a mechanical filter 3 only in the desired frequency bands. The signal output from this mechanical filter 3 is further amplified by an amplifier 4 and sent to an integrator 5. The integrator 5 integrates the output signal of the amplifier 4 so that it has a level corresponding to the frequency. Based on this level, a discrimination circuit placed after the output terminal 6 detects the tone.

In contrast, in recent years, tone detection devices that perform digital processing have appeared, as shown in FIG.

In this device, a signal input from an input terminal 7 is amplified by an amplifier 8 and waveform-shaped by a waveform shaper 9. The waveform-shaped signal is frequency-divided by an N frequency divider 10 and output to a counter 11. A high speed clock is applied to the counter 11 from a clock input terminal 12 . In addition, when the carrier detection circuit 13 that detects the presence or absence of a carrier based on the output signal of the amplifier 8 detects a carrier and sends out a signal to that effect, the counter 11 receives a frequency divided by N by the above-mentioned high-speed clock. Counts one cycle of the branch signal.

This count result is sent to a determining section 14 consisting of a microcomputer whose main components are a microprocessor and a memory, and the determining section 14 performs tone detection based on the magnitude of the above-mentioned count result. The resulting data is sent from the determination unit 14 to another device (not shown) via the output terminal 15.

Comparing these tone detection devices, the digital type can change the frequency range of the tone to be detected by making variable the predetermined value in the comparison between the count result and the predetermined value performed in the determination unit 14. For example, in a table in ROM, there is a power 1 corresponding to tones in various frequency ranges.
The frequency range can be changed by storing the Kund lock. In contrast, with the device shown in FIG. 1, the frequency range of tones that can be detected is fixed, and when detecting tones in various frequency ranges, devices corresponding to each are required.

However, the digital tone detection device is more susceptible to noise than the device using the mechanical filter 3 shown in FIG. For example, if the input signal contains noise and this noise exceeds the threshold of the digital circuit, the period of the input signal is determined to be short by dividing the frequency based on the noise part. Sometimes. In such cases, it may be possible to add hysteresis to the threshold value of the digital circuit, increasing the threshold value in the direction of the threshold value or higher, and lowering the threshold value in the direction of the threshold value or less. . However, even with such a method, there are limits to making the frequency range of the signal in which tone detection is performed a barrier pull, and the method is insufficient.

[Purpose of the invention]

The present invention has been developed in view of the drawbacks of conventional devices as described above. Therefore, the object of the invention is to
It is an object of the present invention to provide a tone detection device which is resistant to noise and whose frequency range of detected signals is variable.

[Summary of the invention]

Therefore, in the present invention, in the digital tone detection device as described above, signal components unnecessary for detecting tones in a specific frequency range are added to the digital tone detection device according to the specific frequency range to be detected. The device 11f is provided with a filter means for changing and removing it.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 3 is a block diagram of an embodiment of the invention.

In the figure, 21 indicates an input terminal. This input terminal 2
The signal input from 1 is filtered by filter means 22 to remove unnecessary signal components in order to detect signals in a specific frequency range. Therefore, this filter means n has the characteristics of a bandpass filter, but must also have the following characteristics. First, it must be a bandpass filter whose band includes the tone frequency you want to detect. And, when the tone frequency to be detected is changed, the bandpass filter can change the band in a variable manner by changing specific parts.

In order to satisfy this condition, in this example,
The filter means 22 is a switched capacitor filter (hereinafter referred to as S, C, F) 2:3, and this S,
C, F', programmable counter 2/! connected to the clock input terminal of 23. It was composed of And S,
The output signals of C, F, 23 are sent to the digital identification circuit 5 which performs the tone detection operation as explained in FIG. did.

Here, the digital identification circuit 5 has a clock input terminal 2.
The ff4J serial clock is input from 7 to perform the operation described in Fig. 2, but a control signal corresponding to the tone frequency to be detected is sent from the microprocessor in the digital identification circuit via the signal line side. It is designed to be given to a programmable counter. The programmable counter frequency divides the clock input from the clock input terminal 29 based on the control signal on the signal line A and outputs it to S, C, F, and 23.

S, C, F, 23 are based on the input clock °C
It changes one band, and its internal configuration includes, for example, a 2111IiI secondary filter, and the required Q can be obtained by using an external resistor.

Generally, in order to configure a filter with certain characteristics, by fixedly providing an external resistor and a clock with a constant period of P), the required characteristics can be freely adjusted (
something that can be fixed or fixed). Of course, the above S, C, F.

What are the characteristics necessary for tone detection, not limited to those with two secondary filters? ', ), other configurations may be used. In this embodiment, by employing a programmable counter 24, a programmable counter 24 is used.

The characteristics of F, '23 themselves are made variable, and in order to determine the characteristics, the digital identification circuit 6 outputs a control signal according to the tone frequency to be detected. It is intended to be given to C, F, 23.

Hereinafter, a specific example of a tone detection device will be described with reference to FIGS. 4 and 5.

In FIG. 4, 4] indicates a detection section, and 12 indicates a processing control section. The signal a L1 shown in FIG.
It is designed to be input to s, c, F, -+s.

The signal having the band-limited and passed band components S, C, F', 45 is waveform-shaped by a waveform shaper 116 and output. This signal S is frequency-divided by an N frequency divider 47 to form a frequency-divided signal C in FIG. This frequency-divided signal C is counted by the high speed clock d (FIG. 5) supplied from the signal line (3) in the counter 48, and the count value is outputted to the parallel I10 port 51. Further, the counter 48 is given a signal indicating that a carrier has been detected from the carrier detection circuit 49, and the counter 48 operates only when this signal is significant.

The above-mentioned parallel I10 port 51 outputs the count value output from the counter 48 to the bus 52 within the processing control section 42 as parallel data of, for example, 8 bits. A microprocessor (hereinafter referred to as CPU) 53, a memory 54, and an I10 unit 55 are connected to this bus 52. Of course, this bus 52K, parallel I10 boat 51 and programmable counter 56
are connected. Further, a signal line 50 for sending out a high-speed clock extends from the CPU 53, and this signal line 50 is connected to the counter 48 and the programmable counter 56, respectively. Then, the CPU 53 supplies data corresponding to the tone frequency to be detected to the programmable counter 56 via the bus 52 according to the program in the memory 54 . Then, based on this data, the programmable counter 56 divides and outputs the high-speed clock given from the signal +1150, and supplies the divided signal to 5-C-F-45. S, C, F
, 45 output the signal It! from the programmable counter 56.
It functions as a bandpass filter for a predetermined band based on the clock outputted through 57.

Next, the tone detection operation will be briefly explained based on the flowchart shown in FIG. The operation line until the count value is output to the parallel I10 port 51 is as described above, and therefore will not be described here. Parallel I10 port 51 sends the count value onto bus 52 as parallel data. Here, the CPU 53 inputs the 1 count value r-11j via the bus 52 in the step of ``input count value n''.Next, the CPU 53 inputs the count value 1 in response to the tone frequency that is currently being detected. 'n J
It is determined whether or not the value exists between the upper limit value and the lower limit value of the DI. That is, first, in the step ``Is nL≦n?'', the CPU 5', 4 judges whether the count value is greater than or equal to the lower limit value nL, and if it is YES, the next step is ``Is n≦n□?''.
The CPU 53 proceeds to step ``.Here, the CPU 53 determines whether the count value r n J is less than or equal to the upper limit value nH.In this step as well, if the branch is made to YES, the CPU 53 determines whether the count value r n J is less than or equal to the upper limit value nH. In the “output” step,
Assuming that the tone is detected once, the CPU 53 uses the example &:
l:, rlJ are stored in the register (in the memory 54), and ?
In order to wait for the count value to be sent from the XK parallel I10 port 51, the process advances to the "wait for count value n" step. Is the above lnL≦n? ” steps and ”n≦n
Is it H? Even if the branch is NO at the step ``, the process proceeds to the step ``Waiting for count value n''.

Such a routine is repeated, and the CPU 53 determines that tone detection has occurred when the data in the register reaches, for example, rmJ.

In the above explanation, the upper limit value ni, the lower limit value nl, and the data given to the programmable counter 5 (i) are
A table corresponding to the tone frequency to be detected is stored in memory 5.
Therefore, since the CPL 153 uses the data in the memory 5.1 differently depending on the tone frequency to be detected, S, C, F depending on
, 45 take appropriate values, and the processing fti control unit 42
Then, appropriate tone detection processing is performed.

〔Effect of the invention〕

As explained above, according to the present invention, the image frequency noise component included in the input signal is removed by the filter means, so even if digital tone detection is performed, threshold 111! It becomes difficult to exceed f. Therefore,
Appropriate 1-tone detection can be performed even when the S/N ratio of the line is very poor, and in terms of noise removal, it is possible to obtain performance that is comparable to a method using a mechanical filter. can.

In addition, the band characteristics of the filter means can be programmably adjusted, so it is possible to guarantee optimal tone detection for all tone frequencies, and tone detection is possible at all frequencies, making it extremely It is a convenient device with both functions.

Furthermore, since there is no need to prepare hardware for each frequency, the configuration can be simple and economical.

In addition to this, the device of the present invention is much more advanced than the conventional device which is equipped with a microcomputer.
- It can be achieved simply by adding software, and the effects are unique to people.

[Brief explanation of drawings]

1 and 2 are block diagrams of a conventional device, FIG. 3 is a block diagram showing an outline of an embodiment of the present invention, FIG. 4 is a block diagram of an embodiment of the present invention, and FIG. 5 is a block diagram of a fourth embodiment of the present invention. FIG. 6 is a waveform diagram for explaining the operation shown in FIG. n...Filter means 23.45...Switched capacitor filter 2
4, 56...Programmable counter 42...Processing control department agent Patent attorney Book 1) Takashi Figure 1 Figure 2 Figure 3 Figure 3

Claims (2)

[Claims] (1) Digital tone detection that detects tones in a specific frequency range by dividing the input signal by N and digitally identifying the period of the resulting frequency-divided signal, and supplying the detection results to the processing control unit. The apparatus is characterized in that it is provided with a filter means for removing unnecessary signal components in order to detect the tone in the specific frequency range in a variable manner according to the specific frequency range of the tone to be detected. Tone detection device. (2) The filter means is a switched capacitor.
The tone detection device according to claim 1, comprising a filter and a programmable counter connected to a clock input terminal of the switched capacitor filter. (: The reprogrammable counter has a count value set based on data output by a microprocessor in the processing control unit according to a specific frequency range of a tone to be detected. ) Tone detection device described in section 2.