JP2968324B2 - Frequency detection method of composite component frequency - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for detecting a composite component frequency of a signal composed of two different frequencies, and removes an undetectable portion of a detection circuit by zero-cross detection using an envelope waveform. An envelope forming unit that forms an envelope waveform of the input signal of the composite component frequency, a zero-cross detector that forms a rectangular wave from the formed envelope waveform, and an output from the zero-cross detector. A composite component frequency detector is provided which partially masks the input signal of the composite component frequency and performs zero-cross detection from a non-masked composite component frequency portion, and counts an output cycle from the composite component frequency detector.

[Industrial applications]

The present invention relates to a method for detecting a composite component frequency of a signal composed of two different frequencies.

Normally, communication signals are exchanged between stations using signals obtained by combining two different frequencies. The MFC signal composed of the two-frequency signal forms a transmission / reception signal by a combination of a high-band frequency signal and a low-band frequency signal, and exchanges transmission signals between stations.

At present, as a commonly used frequency, a high-band frequency signal is composed of six kinds of signals at intervals of 120 Hz from 1380 Hz to 1980 Hz, i.e., 1380, 1500, 1620, 1740, 1860, and 1980 Hz. Frequency signals are six kinds of signals of 540 Hz to 1140 Hz at intervals of 120 Hz, that is, 540, 660, 780, 900, 1020, 1140H
Consists of z. These six kinds of signals are combined two by two, and a combination signal of 15 kinds in each of a high band and a low band is adopted as a dial or a transmission signal and a reception signal of various signals.

The combined frequency of the signal composed of these two different frequencies is important for connection as a transmission / reception signal between the stations, and detection of the combined frequency requires accuracy on the receiving station side.

[Conventional technology]

Synthesis component frequency of a signal that consists of two different frequencies, any two different frequencies and f _1, f _2, when a synthetic component frequency and f _c, is expressed by the following equation.

f _c = (f ₁ + f ₂ ) / 2 For example, the composite component frequency of two kinds of frequencies, 1380 Hz and 1500 Hz, is 1440 Hz. As a method for detecting the combined frequency component f _c, the frequency detecting circuit according to the zero crossing detection with a conventional hysteresis is used.

FIG. 4 shows a conventional detection method. (A) shows a detection circuit, and (b) shows a detection waveform. In the figure, reference numeral 21 denotes a zero-cross detection unit, 22 denotes a counter unit, ′ denotes an input signal waveform, ′ denotes a detection signal waveform, and ′ denotes a counter output.

A hysteresis value of the input signal ', that is, Vth, -Vth, is provided as the upper and lower thresholds, and a waveform exceeding the upper and lower thresholds of the input signal is detected, and a zero-cross detection waveform'
Is transmitted as a rectangular wave, and the counter 22 counts the period of the rectangular waveform to detect the composite frequency. In the zero-cross detection waveform ', a portion where the signal amplitude is large (A in the figure)
Can detect the frequency, but the portion where the amplitude of the signal is small (B in the figure) is not affected by the hysteresis value, so that the frequency cannot be detected. Cannot be performed.

[Problems to be solved by the invention]

As described above, in the frequency detection circuit using the conventional zero-cross detector having hysteresis, the frequency of a small amplitude portion cannot be detected, and the number of samples that can be detected decreases when the threshold is widened, and the frequency increases when the threshold is narrowed. The frequency is disturbed due to the occurrence of a portion and a low portion, and accurate frequency counting cannot be performed.

An object of the present invention is to detect an accurate composite component frequency by using an envelope of a signal waveform composed of two different frequencies.

[Means for solving the problem]

The frequency of the envelope composed of two different types of frequencies is represented by the following equation, where f ₁ and f ₂ are arbitrary different frequencies and f _d is the frequency of the envelope.

f _d = ± [f ₁ −f ₂ ] Since the frequency f _d of this envelope forms an envelope, the composite component frequency is detected using this waveform.

FIG. 1 shows a principle configuration diagram of the detection circuit of the present invention. In the drawing, reference numeral 1 denotes an envelope forming unit that forms an envelope waveform of an input signal having a combined component frequency, 2 denotes a zero-cross detector that forms a rectangular wave from the formed envelope waveform, and 3 denotes a signal from the zero-cross detector. A synthesized component frequency detecting unit that partially masks the input signal of the synthesized component frequency according to the output and performs zero-cross detection from the unmasked synthesized component frequency portion, and a rectangular wave of an unmasked portion detected by the synthesized component frequency detecting unit. 2 shows a counter unit that counts the combined component frequency from.

The envelope forming unit 1 forms an envelope by peak-holding a waveform obtained by full-wave rectifying the input signal. The frequency of the envelope forms the absolute value of the difference between any of the different frequencies, i.e., the AC signal at the difference frequency. The envelope is detected by the zero-cross detector 2 to form ± rectangular waves above and below the zero value, and is input to the composite component frequency detector 3. The composite component frequency detector 3 inputs the composite component signals of two different frequencies, masks the + part of the square wave of the envelope frequency from the zero-cross detector 2, and −
The part outputs the frequency to the counter unit 4 as a rectangular wave.
The counter unit 4 can detect the combined component frequency by counting the period of the rectangular wave by zero-cross detection of the unmasked portion.

[Action]

FIG. 2 shows a principle diagram of the detected waveform of the present invention. In the figure, is an input signal, is an output waveform from the envelope forming unit,
Represents a rectangular wave output waveform from the zero-cross detection unit, a mask of an input signal in the composite component frequency detection unit, a zero-cross detection waveform from the composite component frequency detection unit, and a count cycle from the counter unit.

An input signal is formed by a difference frequency between two different frequencies, and an envelope is formed by a peak hold circuit having a full-wave rectified waveform. The envelope is divided by a zero-cross detection circuit into a portion above 0 and a minus portion below 0 and a rectangular wave with 0 as a boundary is formed. The square wave is intermittent at the same cycle as the difference frequency. The positive side of the rectangular wave is masked and the negative side is not masked, as in the next synthesized component frequency detection unit, and the input signal is subjected to zero-cross detection to transmit the unmasked rectangular wave. Since the rectangular wave is periodically transmitted at the same period as the envelope, the composite component frequency can be detected by counting the periodic frequency portion by the counter section.

〔Example〕

FIG. 3 shows a circuit diagram of an embodiment of the present invention. In the figure, 11 is a double-wave rectifier, 12 is a peak hold unit, 13 is a filter, 14 is a zero-cross detector, 15 is a zero-cross detector, and 16 is a counter.

The input signal (MFP) is a dual-wave rectifier 11 and a zero-cross detector 1
The output (fd) of the zero-cross detector 14 and the output (fc) of the zero-cross detector 15 connected to the filter 13 are connected to the counter 16. Input signal (MFC)
A composite frequency component (fc) and a differential frequency component (fd) synthesized by the input frequencies (f ₁ ) and (f ₂ ) are extracted, and the composite frequency component (fc) is masked by the differential frequency component (fd). The counter 16 detects the cycle of the composite component frequency.

Double-wave rectification unit 11, peak hold unit 12, filter unit 13,
The zero-cross detectors 14 and 15 each include a comparator, a resistor, a rectifier, a capacitor, and the like. The dual-wave rectifier 11 performs full-wave rectification of the MFC signal, envelopes the envelope with an envelope waveform by the peak hold unit 12, and filters the high-frequency unit by the filter unit 13 to extract the envelope waveform. The zero-cross detector 14 performs zero-cross detection on the extracted envelope waveform and sends a rectangular wave of the difference frequency component (fd) to the counter 17.
On the other hand, the zero-cross detector 15 extracts the synthesized frequency component (fc) from the MFC signal and sends out a rectangular wave to the counter 16. The counter section 16 detects the period of the composite component frequency (fc) by masking a portion where the composite signal is not desired to be detected by using the input difference signal, and counts the period by the flip-flop circuit.

〔The invention's effect〕

According to the present invention, by adding an envelope forming circuit and a zero-cross detection circuit of the envelope to a conventional frequency detection circuit based on zero-cross detection and using an envelope waveform,
An undetectable portion of the composite component frequency of a signal composed of two different frequencies can be removed to accurately detect the frequency.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a diagram showing the principle of a detected waveform of the present invention, FIG. 3 is a circuit diagram of the embodiment, and FIG. In the figure, 1 is an envelope forming unit, 2, 14, 15, and 21 are zero-cross detection units, 3 is a combined component frequency detection unit, 4, 16, and 22 are counter units, 11 is a double-wave rectification unit, and 12 is a peak hold unit. Reference numeral 13 denotes a filter unit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04Q 1/45

Claims (1)

(57) [Claims] A method for detecting a composite component frequency of a signal composed of two different frequencies, comprising: an envelope forming section (1) for forming an envelope waveform of an input signal of the composite component frequency; A zero-cross detection unit (2) for forming a rectangular wave from the envelope waveform, and a synthesis for partially masking the input signal of the synthesized component frequency based on the output from the zero-cross detection unit and performing zero-cross detection from the unmasked synthesized component frequency portion A method for detecting a frequency of a composite component frequency, comprising: providing a component frequency detection section (3); and counting an output cycle from the composite component frequency detection section (3).