JPH03247198A - Dtmf signal detection circuit - Google Patents

Abstract

PURPOSE:To simplify a circuit configuration and to decrease the area of the integrated circuit by separating an inputted DTMF signal into a high group frequency component and a low group frequency component, converting a reception tone signal into a rectangular wave signal, inputting a pulse signal and discriminating a tone frequency being a specific frequency. CONSTITUTION:A sinusoidal wave tone signal passing through, e.g. a high group BPF 1 is inputted to a comparator circuit 3, where the signal is converted into a rectangular wave and the converted signal is outputted to a pulse generating circuit 5. A counter 7 uses a pulse signal inputted from the circuit 5 as a reset signal for a binary counter. Then the count is increased for each period of the counter clock signal inputted separately and the count corresponding to the time interval of the pulse signal is outputted. A count inputted from the counter 7 is decoded in a decoder 9 and only a specific frequency signal corresponding to the count is detected and outputted among high group frequencies fH1-fH4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal detection circuit, and in particular, to a signal detection circuit.
The present invention relates to a signal detection circuit used for frequency separation in response to Tone Multi Frequency) signals.

[Conventional technology]

Conventionally, as a signal detection circuit corresponding to DTMF signals,
- By way of example, a circuit as shown in FIG. 3 is used.

In FIG. 3, a tone signal generated in a DTMF signal generation circuit and inputted to an input terminal 60 through a telephone line etc. is filtered through a plurality of bandpass filters (hereinafter abbreviated as BPF) 11a separated into a plurality of frequency bands. ~ll
After the specific frequency components included in the tone signal are selected, each amplitude detector is input to the AM
- abbreviated as DET) 12a, 12b, 12c,...
..., is input at 12h.

In the case of Kono, each B P F 1.2a, t2b, 12c,
As shown in FIG. 4, the bandpass characteristics at -12h are set to low frequencies fL, .about.fL4 and high frequencies fH, .about.fH4, and have the following values.

fLl;697)1z, fL2=770tlz, f
L3=852Hz, fL4=941)1zfH112
09Hz, fH2=1336Hz, fH3=1477
Hz, fH, = 1633HzA M-D E T 12
a, 12b, 12c, --, 12h, each B
The tone signals passing through P F ILa, llb, llc, -=-, llb are detected, and their detection outputs are sent to level comparators (hereinafter abbreviated as CMP) installed for each pass band of each filter. 13a, 13b.

13c, ..., the reference level V at 13h
ref, and the signal level for each frequency band is determined. Therefore, each CM P 13a, 13b, 13
c, -・-=-, 13h are output terminals 61a, 61
b, 6Lc, -・-, 61h, respectively B P
F lla, llb, 11c, ----= , llb
When the detection output corresponding to exceeds the reference level Vrer, a high level is output.

In this case, the correspondence between each output terminal and the receiving frequency is as follows:
It is as follows.

61a-fLt, 61b-fL2.61cmfLs,
61d-fL461e---fJ 61f---f
H2,61g--・fH3,61h-fH4 For example, "
A DTMF signal representing "A" is input from the telephone line etc. to the input terminal 6.
0, the input frequency is DT in FIG.
As is clear from the table showing the correspondence between MF signals and input frequencies, since they are 697Hz and 1633Hz,
Output terminals 61a and 61h become high level, and DT
MF signal "A" is determined. In the same way, selection signals of all tone signal systems are determined.

[Problem to be solved by the invention]

In the conventional DTMF signal detection circuit described above, DT
In order to determine the frequency of the MF signal, a large number of BPFs (
For example, in the case of tone waves with 4 waves in the low group and 4 waves in the high group, 8 BPFs with different bands are required.
The disadvantage is that the layout area within the integrated circuit becomes very large.

In addition, especially when the number of set frequencies for the low group and high group increases, as the frequencies of each tone wave become close to each other, there is a risk of false judgments occurring if the filter's bandpass characteristics are slow. , BPFs are required to have narrow and steep bandpass characteristics, and generally require the use of high-order filters, which have the disadvantage of requiring an extremely large number of man-hours to design.

Furthermore, at low group frequencies, since the frequency is low, the time constant required for amplitude detection becomes large, and the time required for detection becomes long, so when the number of frequencies to be detected increases,
There is also the disadvantage that the detection time is dominated by the detection time of the lowest frequency, and the overall determination time becomes significantly longer.

[Means to solve the problem]

The DTMF detection circuit of the present invention includes an analog filter that separates an input DTMF signal into high frequency components and low frequency components, and means for converting a received tone signal output from the analog filter into a rectangular wave signal. a means for generating a pulse signal at the rise and fall of the rectangular wave signal; and a means for inputting the pulse signal at the rise and fall of the rectangular wave signal to determine a tone frequency of a specific frequency included in the input DTMF signal. and frequency identification means.

Note that as the means for converting the received tone signal into a rectangular wave signal, a comparator circuit using an analog comparator may be used, and the frequency identifying means may include:
A counter circuit that counts a predetermined clock signal using the pulse signal as a reset signal, and a count value output from this counter circuit is decoded, and a tone signal of a specific frequency is determined by referring to the magnitude of the count value. It may also be configured using a decoder.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention.9 As shown in FIG. 1, this embodiment has a high group BPF 1 and a low group BPF.
PF2, comparator circuits 3 and 4, pulse generation circuits 5 and 6, counters 7 and 8, and decoder 9
and 10. The high group BPFI and the low group BPF 2 are analog filters for separating high group frequency components and low group frequency components, and the comparator circuits 3 and 4 are examples of means for converting a received tone signal into a rectangular wave signal. It is.

In FIG. 1, a DTMF tone signal input from a predetermined telephone line to an input terminal 51 is separated into high group frequencies fH1 to fH4 and low group frequencies fL, to fL4 by a high group BPF1 and a low group BPF2. Usually, DTMF
! --As shown in the frequency correspondence table in Fig. 5, the tone signal uses one wave each for the high group and the low group, so the tone signal that has passed through the high group BPF 1 and the low group BPF 2 is It is output as a sheep-frequency sine waveform as shown in Figure 2(a).

Here, in order to simplify the explanation, first, the tone signal detection function on the high group frequency side will be explained. The above-mentioned sine wave tone signal that has passed through the high group BPF 1 is input to a comparator circuit 3 formed using an analog comparator, and is converted into a rectangular wave as shown in FIG. 2(b) and output. and is input to the pulse generation circuit 5. In the pulse generation circuit 5, a pulse signal shown in FIG.

The counter 7 and the decoder 9 are an embodiment of frequency identification means for determining the tone frequency of a specific frequency included in the input DTMF signal. The count value is increased every cycle of a counter clock signal (CLK) that is input separately, and the count value corresponding to the time interval of the pulse signal is output.

Since the pulse signal is generated in the pulse generating circuit 5 every time the sine waveform crosses zero, the time interval of the pulse signal corresponds to a half wavelength of the input sine wave and changes depending on the input frequency. That is, when the input frequency is high, the interval between pulse signals becomes short, and when the input frequency is low, the interval between pulse signals becomes long. For example, the counter clock frequency of a binary counter is 262144
Hz, if the human power frequency is 1209 Hz, the counted value is 108, and if the input frequency is 1633 Hz, the counted value is 80. Therefore, the counter 7 outputs a count value corresponding to the input frequency and inputs it to the decoder 9.

In the decoder 9, the count value input from the counter 7 is decoded, and only a specific frequency corresponding to the count value among the high group frequencies fH1 to fH4 is detected and output. Output terminal 52.53.54
and 55 are the high group frequencies fHr, f)I, respectively
z, fH3, and fH4, and only the output terminal corresponding to the detection frequency among the output terminals 52 to 55 becomes high level, and the D
The input frequency of the TMF signal is determined. For example, when the input frequency is 1209Hz(f)l, ), only the output terminal 52 becomes high level, and the input frequency is 1209Hz(f)l,
It is determined that the frequency is 9Hz.

Note that the same applies to the tone signal detection function on the low group frequency side, and the sinusoidal tone signal that has passed through the low group BPF 2 is transmitted through the comparator circuit 4, pulse generation circuit 6, counter circuit 8, and decoder 10, respectively. Low group frequencies fL,, fL2. Output terminals 56 , 57 , formed as output terminals corresponding to fL3 and fL4
The input frequency is determined based on the output level of the output terminal corresponding to each detected frequency in 58 and 59.

〔Effect of the invention〕

As described above in detail, the present invention greatly simplifies the circuit configuration because it is not necessary to install all the bandpass filters corresponding to the respective frequencies for the tone signals of multiple frequencies included in the DTMF signal. It is possible to
This has the effect of reducing the layout area of the integrated circuit and keeping the chip cost low. It also eliminates the need for designing high-order filters and further shortens the judgment time for DTMF signal detection. It has the effect of being able to

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
a), (b) and (C) are signal waveform diagrams in the above embodiment, FIG. 3 is a block diagram showing the conventional example, FIG. 4 is a diagram showing the bandpass characteristics of BPF, and FIG. FIG. 3 is a diagram showing a frequency correspondence table between DTMF signals and input frequencies. In the figure, 1...high group BPF, 2...-
-Low group BPF, 3, 4... comparator circuit,
5, 6... Pulse generation circuit, 7, 8...
...Counter, 9. IO...Decoder, l
la, 11bJlc, ~llb --------B P
F, 12a 12b 12c, ~12h ・----
・AM-DET, 13a, 13b. Dc, ~13h...CMP.

Claims (1)

[Claims] 1. An analog filter that separates an input DTMF signal into high frequency components and low frequency components; and converts a received tone signal output from the analog filter into a rectangular wave signal. means for generating a pulse signal at the rise and fall of the rectangular wave signal; inputting the pulse signal at the rise and fall of the rectangular wave signal;
A DTMF signal detection circuit comprising: frequency identification means for determining a tone frequency of a specific frequency included in the input DTMF signal. 2. The DTM according to claim 1, wherein the means for converting the received tone signal into a rectangular wave signal is constituted by a comparator circuit using an analog comparator.
F signal detection circuit. 3. The frequency identification means includes a counter circuit that counts a predetermined clock signal using the pulse signal as a reset signal, decodes the count value output from the counter circuit, and identifies the count value by referring to the magnitude of the count value. 2. The DTMF signal detection circuit according to claim 1, further comprising: a decoder for determining a tone signal having a frequency of .