JPH08313566A - Frequency detector - Google Patents

Abstract

PURPOSE: To simplify the constitution of a frequency detector so as to reduce the cost of the detector by providing a detector adaptable to such a case that the frequencies of monotone signals to be detected are different from each other. CONSTITUTION: A comparator 14 converts inputted analog signals into rectangular-wave digital signals. A counter 15 inputs the digital signals and obtains a count value by counting the number of the leading edges of the signals only during prescribed operating time set in a timer 19. A control section 18 calculates the received frequency from the count value and operating time of the counter 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency detector for detecting the frequency of an input signal.

[0002]

2. Description of the Related Art Conventionally, for example, a frequency detector shown in FIG. 4 has been known. This frequency detector is provided in, for example, a facsimile machine, and detects the frequency of an analog single tone signal received via a telephone line. Further, the frequency detector is connected to a bandpass filter 1 to which an analog signal is input, an energy detector 2 to which an output terminal of the bandpass filter 1 is connected, and an output terminal of the energy detector 2. With
The control unit 3 sets the filter coefficient of the bandpass filter 1. In this frequency detector, the control unit 3 sets the filter coefficient of the bandpass filter 1 according to the frequency to be detected, and determines the value output via the bandpass filter 1 and the energy detector 2. By doing so, it is possible to detect whether or not there is an input of a specific frequency.

[0003]

However, in the above-mentioned conventional configuration, in order to detect the frequencies of a plurality of single tones, it is necessary to provide a plurality of frequency detectors, which increases the circuit scale and reduces the cost. It has problems such as rising prices.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a frequency detector capable of detecting a plurality of frequencies with a simple structure.

[0005]

A frequency detector of the present invention comprises a rectangular wave converting means for converting an input signal into a rectangular wave, and a counter for measuring the number of rectangular waves output by the rectangular wave converting means. A timer for measuring the operation time of the counter and a control unit for calculating the frequency from the measurement result of the counter and the operation time of the timer are provided.

[0006]

In the frequency detector of the present invention, the input signal is converted into a rectangular wave by the rectangular wave converting means. And the number of this square wave, during the operation time that the timer measures,
The counter measures. Then, the control unit calculates the frequency from the measurement result of the counter and the operation time.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of one embodiment of the frequency detector of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 11 denotes a frequency detector. This frequency detector 11 is provided in, for example, a facsimile machine and is a so-called tone detector for detecting the frequency of an analog tone signal received through a public telephone line. It is supposed to function as.

The frequency detector 11 has an analog input terminal 12 connected to a public telephone line or the like, and the analog input terminal 12 is connected to an input terminal of a comparator 14 as a rectangular wave converting means. . Then, in the comparator 14, the reference voltage as a threshold is set to 0V, and the output is 0V when the input signal is 0V, as shown in FIG.
In the above positive state, it becomes H, while in the negative state it becomes L,
It converts the input analog signal into a digital rectangular wave and outputs it.

The output terminal of the comparator 14 is
It is connected to the input terminal of the counter 15, and this counter 15
It is designed to measure the number of rising edges of a rectangular wave. The output terminal of the counter value output unit 16 that outputs the counter value that is the measurement result of the counter 15 is connected to the input terminal of the control unit 18.

Further, the control unit 18 is connected to a timer 19, and the control unit 18 controls the operation of the timer 19 for setting and the operation time of the counter 15 is set by the data input from the timer 19. T0 is managed. Further, the output terminal of the control unit 18 is the enable terminal (ENABLE) and the clear terminal (CLEA) of the counter 15.
R). Then, the counter 15 performs the measurement operation only when the enable terminal is on, and clears the counter value when the clear terminal is on.

Next, referring to the flowchart of FIG.
The operation of the frequency detector 11 will be described.

First, the control unit 18 turns on the clear terminal of the counter 15 to clear the counter value (step 1).

Subsequently, the control unit 18 clears the value of the timer 19, starts the timer 19, and turns on the enable terminal of the counter 15 (step 2). Then, in this state, the value of the timer 19 is T0
The number of rising edges of the rectangular wave output from the comparator 14 is measured during this period (step 3).

When the value of the timer 19 reaches T0 seconds, the enable terminal of the counter 15 is turned off (step 4) and the measurement is completed.

In this state, the control unit 18 reads the counter value X, which is the number of measured edges, from the counter value output unit 16 (step 5) and sets the frequency f [Hz] = X / T0 [second]. By substituting into the formula, the received frequency can be calculated and it can be detected whether it is a predetermined frequency (step 6).

As described above, according to the frequency detector 11 of the present embodiment, the counter 15 is operated only for a certain period of time, and the frequency of the received signal can be calculated from the counter value and the operating time at this time. Even when there are a plurality of frequencies of a single tone signal at the same time, a single device can be used, the configuration can be simplified, the manufacturing cost can be reduced, and the device can be downsized.

In the above embodiment, the counter 15 is
I measured the rising edge of the input square wave,
For example, the number of falling edges may be measured.

[0019]

According to the frequency detector of the present invention, the input signal is converted into a rectangular wave by the rectangular wave converting means, and the number of this rectangular wave is measured by the counter during the operation time of the timer. Then, the frequency can be calculated by the control unit from the measurement result of these counters and the operating time. Therefore, even when there are a plurality of frequencies of signals to be detected at the same time, one device can be used, and the configuration can be simplified and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a frequency detector of the present invention.

FIG. 2 is a waveform diagram showing an input signal and an output signal of the comparator of the frequency detector.

FIG. 3 is a flowchart showing the operation of the frequency detector of the above.

FIG. 4 is a configuration diagram showing a conventional frequency detector.

[Explanation of symbols]

 11 Frequency detector 14 Comparator as a rectangular wave converter 15 Counter 18 Controller 19 Timer

Claims (1)

[Claims] 1. A rectangular wave conversion means for converting an input signal into a rectangular wave, a counter for measuring the number of rectangular waves output by the rectangular wave conversion means, and a timer for measuring the operating time of the counter, A frequency detector comprising: a control unit that calculates a frequency from a measurement result of a counter and an operation time measured by the timer.