JPH0927828A - Modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an undesired frequency component, to avoid frequency selection of an oscillator from begin limited and to improve the reliability. SOLUTION: Outputs of oscillators 1a, 1b whose oscillated frequencies f1, f2 differ from each other are inputted to a switch circuit 2, by which the frequency output is switched corresponding to '0', '1' of digital transmission data and outputs it. Then a waveform code generating circuit 7 provides an outputs an optional repetitive waveform code such as a reversible up/down count valve and a waveform conversion circuit 8 generates the waveform generating code corresponding to the waveform code while referencing a table. A D/A converter circuit 9 converts a digital modulation output from the waveform conversion circuit 8 into an analog modulation output.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to FSK (frequency
shift keying) The present invention relates to a modulation device that performs modulation.

[0002]

2. Description of the Related Art A data signal transmission device or the like is equipped with a modulation device for performing transmission modulation. FIG. 3 is a diagram showing a schematic configuration of a conventional modulator that performs this type of FSK modulation.

The modulator shown in FIG. 3 is of a direct switching type FSK modulation system, and includes two oscillators 1 having different oscillation frequencies.
a, 1b, a switch circuit 2 for switching the output, and a bandpass filter (BPF) 3.

Signals of frequencies f1 and f2 are output from the oscillators 1a and 1b, respectively, and the switch circuit 2 corresponds to the digital transmission data "0" and "1".
The signals f1 and f2 are selected and switched. Thereby, a predetermined FSK modulation output can be taken out. The bandpass filter 3 is a passband limiting filter used when the oscillators 1a and 1b output rectangular wave outputs and analog modulation outputs.

FIG. 4 is a block diagram showing a schematic configuration of a conventional frequency division type FSK modulation type modulator. This modulator is composed of a single oscillator 1, a frequency divider 4, a frequency division ratio setting circuit 5 and a flip-flop 6, and a band pass filter 3 is provided if necessary as in the above case.

The output of the oscillator 1 having the frequency f0 is divided into desired frequencies by the frequency divider 4, and the divided frequencies are switched and output. At that time, the setting of the frequency division ratio is switched corresponding to "0" and "1" of the digital transmission data, whereby the FSK modulation output can be taken out. Further, when the analog modulation output is desired to be taken out, the modulation output is obtained through the bandpass filter 3.

[0007]

By the way, in the conventional direct switching FSK modulator shown in FIG. 3, a phase discontinuity occurs at the time of directly switching between two frequencies in accordance with digital transmission data. Generates high frequency components. Therefore, there are the following problems.

(A) An unnecessary (harmful) high frequency component other than the original frequency is output.

(B) On the side that receives and demodulates the modulated signal, the high frequency component becomes a noise component, and the S / N (C /
N) Ratio decreases.

(C) On the side of demodulating the same modulated signal, an unstable time of the signal occurs at the time of demodulation, and the quality of data transmission, that is, reliability is deteriorated.

In the conventional frequency division type FSK modulator shown in FIG. 4, the phase discontinuity as described above is eliminated, but the frequency division ratio setting ratio is a positive integer. In order to create two types of output frequencies, it is necessary to select the frequency of the oscillator so that it is the least common multiple of both frequencies. Also, switching of the division ratio and acquisition of digital transmission data are performed by the frequency divider. Since the overflow (OF) output is performed, there are the following problems.

(D) There is a limitation in selecting the frequency of the oscillator.

(E) There is a time difference between the switching time point of the digital transmission data and the switching time point of the modulation output, and this time difference makes one cycle of the frequency divider overflow cycle (one cycle of the modulation output frequency) maximum. It fluctuates depending on the time.

(F) Due to the above (e), jitter (fluctuation) of data occurs when demodulated on the receiving side, and the reliability of data transmission decreases.

The present invention has been made by paying attention to the above-mentioned problems, has a small number of unnecessary frequency components, improves the S / N ratio, and has no restriction on the selection of the frequency of the oscillator. It is an object of the present invention to provide an improved modulator.

[0016]

A modulator according to the present invention comprises a plurality of oscillators that generate signals of different frequencies, and a switch circuit that selects and outputs a desired signal from the frequency signals output from these oscillators. And a waveform code generation circuit for generating an arbitrary repetitive waveform code according to the output of the switch circuit, and a waveform conversion circuit for outputting a waveform generation code corresponding to the waveform code.

In the above modulator, the digital modulation output of the waveform conversion circuit is converted to an analog modulation output D.
A / A conversion circuit is provided.

The above-mentioned waveform code generation circuit is composed of a counter capable of up-counting and down-counting operations.

[0019]

1 is a block diagram showing a schematic configuration of an FSK modulator according to the present invention. In the figure, 1a,
1b is an oscillator that generates signals of different frequencies f1 and f2, and 2 is a switch circuit that selects and outputs a desired signal from the frequency signals output from these oscillators 1a and 1b. The frequencies f1 and f2 are selected corresponding to "1".

Reference numeral 7 is a waveform code generation circuit for generating an arbitrary repetitive waveform code according to the output of the switch circuit 2 and is a U code capable of up-counting and down-counting operations.
It is composed of a P / DOWN counter.

Reference numeral 8 denotes a waveform conversion circuit which outputs a waveform generation code corresponding to the generated waveform code, and stores the waveform conversion data as a table. Reference numeral 9 is a D / A conversion circuit for converting the digital modulation output of the waveform conversion circuit 8 into an analog modulation output.

Here, with respect to the output frequencies f1 and f2 of the oscillators 1a and 1b, the FSK modulation output frequencies fm1 and f2 are obtained.
m2 is fm1 = 2 × n × f1, fm2 = 2 × n × f2, where n is the count value of the waveform code generation circuit 7.
It is set so that

FIG. 2 shows the signal waveform of each part (A to G) of FIG. The outputs of the two oscillators 1a and 1b are input to the switch circuit 2, and the frequencies f1 and f2 are selected and output according to "0" and "1" of the digital transmission data. The output of the switch circuit 2 is input to the waveform code generation circuit 7, where a reversible up / down count operation is performed according to the output pulse of the switch circuit 2.

At this time, for example, when the count value of the counter is octal, the initial count value is "0",
Every time a pulse is input from the switch circuit 2, the count value is “0” → “1” → “2” → …… → “6” → “7” →
“8” → “7” → “6” → …… “2” → “1” → “0”
→ "1" → ... changes.

The output of the waveform code generation circuit 7 is composed of multiple bits and is input to the waveform conversion circuit 8 in the next stage, from which the waveform generation code corresponding to the output code of the waveform code generation circuit 7 (see FIG. 2). In the example, the S / N wave code)
Is output. The waveform generation code converted by the waveform conversion circuit 5 is input to the D / A conversion circuit 9, and an actual S / N wave approximate waveform signal is output from this.

The FSK modulation output is obtained in this manner. In this example, one cycle of the modulation output frequency is subdivided by twice the number of counts of the counter, and is generated.
At the time of switching the modulation output frequency, the time corresponding to one count of this counter only fluctuates within the range of one cycle of the oscillators 1a and 1b.

Therefore, since the modulation output has a small amount of jitter (blurring), the S / N ratio is improved, and the continuity of the waveform is not lost at all, a highly reliable modulation output with very few unnecessary frequency components. Can be obtained.

The modulation output frequency is switched by the first output pulse of the oscillator 1a, 1b after the digital transmission data is switched and the output selection of the oscillator 1a, 1b by the switch circuit 2 is switched. , There is almost no time difference from the time of switching the digital transmission data.

Further, if the number of cycles of the modulation frequency required for demodulation can be secured, it is possible to cope with any transmission rate, the frequencies of the oscillators 1a and 1b can be freely selected, and the target output frequency can be continuously switched. Is done.

By increasing the number of oscillators, that is, the types of frequencies, and increasing the number of switch circuits and the number of bits of digital transmission data accordingly, it is possible to increase the types of modulation output frequencies and to increase the number of multi-valued signals. It also becomes possible to transmit digital data.

By changing the conversion method of the waveform conversion circuit 8, waveform signals other than the S / N wave of this example can be output.

[0032]

As described above, according to the present invention, there are few unnecessary frequency components, the S / N ratio is improved, the frequency of the oscillator is not limited, and the reliability is improved. can get.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a modulation device according to the present invention.

FIG. 2 is a signal waveform diagram of each part in FIG.

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a block diagram showing another conventional example.

[Explanation of symbols]

 1a oscillator 1b oscillator 2 switch circuit 7 waveform code generation circuit 8 waveform conversion circuit 9 D / A conversion circuit

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[Procedure amendment]

[Submission date] August 15, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

[0008] (i) other than the original frequency of unnecessary resulting in output of the (harmful) high-frequency component.

[Procedure amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction contents]

The output of the waveform code generation circuit 7 is composed of multiple bits and is input to the waveform conversion circuit 8 in the next stage, from which the waveform generation code corresponding to the output code of the waveform code generation circuit 7 (see FIG. 2). cord S I N waves in the example)
Is output. The waveform converting waveform generated code conversion circuit 5 is input to the D / A conversion circuit 9, the signal of the actual S I N wave approximation waveform from which is output.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction contents]

Further, by changing the conversion system of the waveform converting circuit 8 can output a waveform signal other than S I N wave in this example.

Claims (3)

[Claims] 1. A plurality of oscillators that generate signals of different frequencies, a switch circuit that selects and outputs a desired signal from the frequency signals output from these oscillators, and an arbitrary repetitive waveform according to the output of this switch circuit. A modulation device comprising: a waveform code generation circuit for generating a code; and a waveform conversion circuit for outputting a waveform generation code corresponding to the waveform code. 2. The modulator according to claim 1, further comprising a D / A conversion circuit for converting a digital modulation output of the waveform conversion circuit into an analog modulation output. 3. The modulator according to claim 1, wherein the waveform code generation circuit is composed of a counter capable of up-counting and down-counting operations.