JPH0253984B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tone signal detection device that is less likely to malfunction due to noise and is suitable for IC implementation.

Generally, a tone signal detection device used when transmitting information or control signals from a base station to a mobile radio device in the form of a tone signal uses a highly accurate filter. Therefore, manufacturing of the device requires highly accurate adjustment, and the device has the disadvantage that its performance deteriorates due to vibration, temperature change, and aging.

In addition, a tone detection device that consists of a reference frequency clock generation circuit and a counter, and detects a tone signal by counting the number of clocks within one cycle of the tone signal, is susceptible to noise such as fading that is unique to mobile radio. The drawbacks were that sensitivity deteriorated and malfunctions were more likely to occur.

The present invention eliminates the above-mentioned problems and provides a tone signal detection device that can receive tone signals in noise with high sensitivity, has fewer malfunctions due to noise, is stable against vibrations and temperature fluctuations, and is suitable for IC implementation. An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a terminal to which a received signal is input, and 2 is an input conversion circuit for converting the input signal into a rectangular wave, which is composed of, for example, a voltage comparator. Reference numeral 3 denotes a gate control circuit which opens the gate 4 during, for example, three periods of the input signal, and applies the reference frequency from the reference frequency generation circuit 5 to the period measurement counter 6. Note that the gate control circuit 3, as shown in FIG.
Generally, it is opened for a certain period of time (as shown in C) in synchronization with the rise of a rectangular wave. 7 is a frequency determination circuit that determines whether the input signal is a tone signal to be detected from the contents of the period measurement counter 6; 8 is a measurement number counter that counts the number of times the period of the input signal is measured; 9 is a frequency determination circuit of the frequency determination circuit 7; A frequency coincidence counter 10 counts the output, and a signal detection threshold circuit 10 compares the contents of the measurement number counter 8 and the frequency coincidence counter 9 to determine tone signal detection. 11 is a terminal from which a tone signal detection output signal is generated.

Figure 2 shows the signal waveforms of the main parts, where A is the input signal applied to terminal 1, B is the output of the input conversion circuit 2, C is the output of the gate control circuit 3, and D is the output of the reference frequency generation circuit 5. , E is the output of gate circuit 4,
to is the count value of the period measurement counter 9, and g is the output of the frequency determination circuit 7.

Figure 3 shows the operation in other states,
A is the count value of the measurement number counter 8, B is the output of the frequency determination circuit 7, C is the count value of the frequency coincidence counter 9, and D is the output of the signal detection threshold circuit 10.

The frequency of the tone signal to be detected next is 950Hz~
1050Hz, the frequency generated by the reference frequency generation circuit is
The operation of the above embodiment will be explained in the case of 100KHz.

If the input signal shown in Figure 2A is applied to terminal 1,
The input conversion circuit 2 converts the signal into a rectangular wave as shown in FIG. 2B. Further, a reference frequency generating circuit 5 composed of a crystal oscillator circuit generates a pulse of 100 KHz.
The gate control circuit 3 is composed of, for example, a frequency dividing circuit, and operates the gate circuit 4 during four periods of the input signal as shown in FIG. 2C to generate the output shown in FIG. 2E. The output of this gate circuit 4 is counted by a period measurement counter 6. FIG. 2 is a diagram in which the value of the period measurement counter 6 is plotted on the vertical axis, and when the frequency of the input signal applied to the terminal is from 950 Hz to 1050 Hz, the final value of the period measurement counter 6 is about 421 from about 381.

100 (KHz) x 1/950 (Hz) x 4 (period) ≒ 421 100 (KHz) x 1/1050 (Hz) x 4 (period) ≒ 381 The frequency judgment circuit 7 determines that the value of the period measurement counter 6 is
When the value is from 381 to 421, that is, when the frequency of input signal A is 950 to 1050 Hz, an output is generated as shown in FIG.

The measurement counter 8 is composed of a decimal counter, and counts the output of the gate control circuit 3 as shown in FIG. 3A. When the frequency measurement of the input signal applied to terminal 1 is repeated 10 times, the signal detection threshold circuit 10
make it work. A frequency coincidence counter 9 counts the output of the frequency determination circuit 7 shown in FIG. 3B. Third
Figure C shows the value of the frequency match counter 9 on the vertical axis, and the signal detection threshold circuit 10 determines the presence or absence of a tone signal based on the value of the frequency match counter 9 at the end of 10 measurements. The output waveform when the value of the frequency coincidence counter 9 is set to 5 as a criterion for determination is shown in FIG. 3D.

As is clear from the above embodiments, according to the present invention, the frequency of an input signal is measured many times, and tone signal detection is determined when the frequency of a tone signal is determined with a certain probability or more. Tone signals can be detected with high sensitivity even when the noise level is high, such as in the case of Also, since most circuits can be constructed with digital circuits,
It is possible to provide a tone detection device that is easy to integrate into an IC, does not require adjustment, and is stable against vibrations and temperature fluctuations. Furthermore, since the above-mentioned frequency measurement is performed based on the built-in reference frequency, it can be extremely stable, and since the determination is made based on the probability of occurrence of the number of matches within a certain period of time, the influence of fading It has the advantage of being less susceptible to In addition, tone signal detection can be improved by cumulatively counting the wave number of the reference signal over multiple periods of the signal (first time) to eliminate short-term effects such as short momentary pulse noise. For long-term fluctuations, the device is configured to count multiple times of the first time period (second time period) to make a judgment, so it has the feature of being able to perform highly accurate measurements under noise in both long and short periods. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tone signal detection device according to an embodiment of the present invention, and FIGS. 2 and 3 are signal waveform diagrams for explaining its operation. 4...Gate circuit, 5...Reference frequency generation circuit, 6...Period measurement counter, 9...Frequency matching counter, 10...Signal detection threshold circuit.

Claims (1)

[Claims] 1 The first integer multiple period of the input tone signal of the radio
Measuring means for measuring the frequency of the input signal by counting the number of waveforms of the reference frequency signal that enters within the time based on the output of a built-in reference frequency generation circuit, and the number of times the frequency of the input signal matches the desired frequency. A tone signal detecting device characterized in that it is provided with determining means for determining tone signal detection when the probability exceeds a predetermined predetermined probability within a time that is an integral multiple of the first time.