JPH0846651A - Fsk modulation system - Google Patents

Abstract

PURPOSE:To eliminate the occurrence of harmonics at signal switching and to make a data output stable after demodulation by providing a frequency- divider whose frequency division ratio is set and frequency-dividing an output of an oscillator depending on a base band signal. CONSTITUTION:This system is provided with an oscillator 1 outputting a signal with a prescribed frequency and a 1/N frequency divider 2 whose frequency division ratio 1/N (N is an integer) is set with respect to an oscillated output, and the frequency divider 2 is constituted of a 4-bit conventional binary counter in this embodiment and has an overflow(OVF) output terminal, setting terminals (n0-n3) to count up the count from an optional count and an input terminal (LOAD) used to receive the count. Then digital data to be transmitted are received as a setting value of the 1/n frequency divider 2 from an OVF output generated by the 1/N frequency divider 2. When the level of the data is '0', an output (clock) of the oscillator 1 is subject to 1/9 frequency division and when the level of the data is '1', an output (clock) of the oscillator 1 is subject to 1/8 frequency division, and then the OVF output is waveform-shaped by a 1/2 frequency divider 3 or the like, from which a modulation output is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FSK (frequency shift keyin) used, for example, in a modulation circuit for data transmission.
g) Concerning the modulation method.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a circuit configuration of a general FSK modulation system. In the figure, 11 and 12 are oscillators that output signals of different frequencies f1 and f2, respectively.
Reference numeral 13 is a switch for switching those oscillation outputs according to the digital baseband signal.

Normal FSK modulation is a method of electrically switching between two frequencies f1 and f2 corresponding to "0" and "1" of a digital baseband signal to be transmitted. In the example of FIG. 3, when the digital data input to the switch 13 is “0”, the frequency f1 of the oscillator 11 is output, and when the digital data is “1”, the frequency f2 of the oscillator 12 is output.

FIG. 4 shows the relationship between the baseband signal and the FSK modulation output. As shown in the figure, the frequency of the modulation output changes every time the baseband signal changes. Further, FIG. 5 is an enlarged view of an output waveform obtained by FSK demodulating the modulated output portion B when the baseband signal is switched from "0" to "1".

[0005]

By the way, in the conventional FSK modulation method as described above, when the frequencies f1 and f2 are simply switched to the input digital data, the digital data is changed from "0" to "0". Since the frequencies f1 and f2 are out of phase when changing from "1" and "1" to "0", many modulated components, that is, components unrelated to the frequencies f1 and f2, are included in the modulation output. .

Therefore, when the modulated output is demodulated, the output portion at the time of the above switching becomes an indefinite area B as shown in FIG. 5, and jitter or the like appears in the output and becomes unstable. In particular, this phenomenon becomes remarkable when the transmission rate is high and the change in digital data becomes short, and in some cases, demodulation cannot be performed at all.

Although various methods have been proposed for the FSK demodulation method, in any method, the high frequency component generated from the modulation side has an adverse effect.

The present invention has been made by paying attention to the problems as described above. It is possible to eliminate the generation of harmonic components at the time of signal switching, stabilize the data output after demodulation, and reduce the cost. The aim is to provide a possible FSK modulation scheme.

[0009]

The FSK modulation system of the present invention comprises an oscillator and a frequency divider capable of setting a frequency division value of its oscillation output, and responds to a baseband signal for frequency shifting. It is configured to generate different frequency outputs by setting the frequency division value of the frequency divider.

[0010]

In the FSK modulation system of the present invention, the frequency division value of the frequency divider is set in accordance with the baseband signal, and the signal input from the oscillator is divided by the set frequency division value to make it different. A frequency output is produced.

[0011]

1 is a block diagram showing the system circuit configuration of an embodiment of the present invention. In the figure, 1 is an oscillator that outputs a signal of a predetermined frequency, and 2 is a frequency division value 1 of the oscillation output.
/ N (N is an integer) is a 1 / N frequency divider, and in this example, it is composed of a 4-bit normal binary counter so that it can count up from the overflow output (OVF) and any count value. Setting terminals (n0 to n3) and an input terminal (LOA
D) and.

Reference numeral 3 is a 1/2 frequency divider circuit composed of flip-flop circuits, 4 is a low-pass filter (LPF), 5 is a latch composed of D-type flip-flops, and a digital baseband signal for frequency shifting is provided. Entered, Q
And the inverted Q output are set terminals (n0 to n) of the frequency divider 2.
3) is input (n0: LSB, n3: MSB). The clock terminal of the latch 5 is connected to the output terminal (OVF) of the frequency divider 2.

In the circuit configured as described above,
By the overflow output generated by the 1 / N frequency divider 2,
The digital data to be transmitted is taken in as the setting value of the 1 / N frequency divider 2. Here, when the data is "0", the output (clock) of the oscillator 1 is divided by 9, and when it is "1", it is divided by 8, and the overflow output is waveform-shaped by the 1/2 divider circuit 3 or the like. , Obtain the target modulation output.

FIG. 2 is a timing chart showing the signal waveforms of the respective portions A to E in FIG. 1. FIG. 2A is an enlarged waveform of the portions A to D, and FIG. 2B is a baseband signal of the portion D. The modulation outputs of the C and E parts for the are shown.

Since the output at the portion C in FIG. 1 is a digital output, if a sine wave output is required, it is passed through the low pass filter 4 or the like. Further, the frequencies f1 and f2 of the modulation output are f1 = f /, where f is the output frequency of the original oscillator 1.
(2 × 9), f2 = f / (2 × 8).

Here, if the bit rate of the data to be transmitted (transmission time per bit) is S (bps),
S × f1 = n1, S × f2 = n2 (n1 and n2 are integers)
Is ideal. At this time, f1 and f2 are generated in synchronization with an integer number of times within S time.

Therefore, the frequency division ratio N1 required to generate the original oscillation frequency f and the frequency f1 and the frequency division ratio N2 required to generate the frequency f2 are defined by these conditions. Just decide.

As described above, since one oscillator 1 and one frequency divider 2 are used to generate two carrier frequencies f1 and f2 corresponding to a digital signal, the transmission is performed. It is possible to completely eliminate high-frequency harmonic components when the data changes, and the data output after demodulation becomes stable. Moreover, since two frequencies are generated by one oscillating element, it is possible to reduce the cost.

[0019]

As described above, according to the present invention, a frequency divider capable of setting a frequency division value is provided and frequency outputs are generated by dividing the output of an oscillator according to a baseband signal. Therefore, it is possible to eliminate the generation of harmonic components at the time of signal switching, stabilize the data output after demodulation, and reduce the cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is a timing chart showing signal waveforms of various parts shown in FIG.

FIG. 3 is a block diagram showing a circuit configuration of a conventional example.

4 is a timing diagram showing the relationship between the baseband signal and the modulation output of the circuit of FIG.

5 is an explanatory diagram showing an enlarged demodulation output of the portion A in FIG.

[Explanation of symbols]

 1 Oscillator 2 1 / N divider 3 1/2 divider circuit 4 Low-pass filter 5 Latch

Claims (1)

[Claims] 1. An oscillator and a frequency divider capable of setting a frequency division value of its oscillation output, wherein the frequency division value of the frequency divider is set according to a baseband signal for frequency shifting. To generate different frequency outputs according to
SK modulation method.