JP2000270030A - Fsk signal demodulating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the cost of an FSK receiver by constituting a demodulating circuit for a FSK signal without using a multiplier entailing an increase in the number of components. SOLUTION: An FSK signal of down-converted intermediate frequency is converted by an A/D converter 1 into a digital signal, which is inputted to a CPU; and a Fourier transformation part 3 transforms a signal varying in value with time into frequency spectrum data and inputs the data to a frequency decision part 4 to decide a code word. When a multi-valued FSK signal is demodulated, the program of the CPU is rewritten for the demodulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an FSK (Frequency S)
Hift Keying) signal demodulation circuit.

[0002]

2. Description of the Related Art A demodulation circuit used in an FSK signal receiver includes a synchronous detection method and a delay detection method. The synchronous detection method is composed of a carrier recovery circuit, a multiplier, a filter, a phase detector, and a differentiation circuit. In addition, the delay detection method includes a delay circuit, a multiplier, a filter, a phase detector, and a differentiating circuit, and has a problem in that each of the delay detection methods must include a multiplier that increases the number of components.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an FSK signal demodulation circuit which eliminates the need for a multiplier which leads to an increase in the number of components and which can reduce the cost of an FSK receiver.

[0004]

In order to achieve the above object, an FSK signal demodulation circuit according to the present invention comprises: an A / D converter for sampling an FSK signal and converting it to a digital signal; And a frequency determination unit that determines and outputs a codeword from the frequency of the signal from the arithmetic circuit.

Note that a circuit that performs a Fourier transform operation is used as the operation circuit.

[0006] A frequency determination unit having a code word determination function corresponding to the number of bits of the FSK signal is used.

[0007] The frequency determination section may use a rewriteable program for determining a codeword in accordance with the number of bits of the FSK signal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. FIG. 1 shows an FSK according to the present invention.
FIG. 3 is a block diagram of a main part of an embodiment of a signal demodulation circuit. In the figure, reference numeral 1 denotes an A / D converter, which samples an FSK signal converted into an intermediate frequency and converts it into a digital signal. Reference numeral 2 denotes a CPU, which includes a Fourier transform unit 3, a frequency determination unit 4, and a control unit 5. The Fourier transform unit 3 (arithmetic circuit) converts a signal whose value changes with time from the A / D converter 1 into frequency spectrum data. After conversion, the codeword is determined from the frequency of the spectrum by the frequency determination unit 4.
The control unit 5 controls the Fourier transform unit 3 and the frequency determination unit 4.

Next, the operation of the FSK signal demodulation circuit according to the present invention will be described. The FSK-modulated signal is down-converted by a high frequency circuit, amplified by an intermediate frequency amplifier circuit, and
/ D converter 1 The A / D converter 1 samples the input FSK signal with a clock having a frequency twice or more the maximum frequency of the codeword converted by the subsequent Fourier transform unit 3 and converts it into a digital signal. This signal is input to the CPU 2 and calculated by the Fourier transform unit 3 which is an arithmetic circuit. A signal whose value changes with time as shown in FIG. 2A is converted into data of the frequency spectrum shown in FIG. Fourier transform (represented by a line spectrum at a predetermined frequency) (according to the Fourier transform formula). Each of the FSK-modulated codewords has a predetermined frequency (for example, FS
If the K signal is binary, it corresponds to f1 or f2). For example, at the input of the first codeword, a line spectrum appears at the frequency f1 by Fourier transform, and at the input of the second codeword. , A line spectrum appears at the frequency f2. That is, the FSK signal is demodulated by Fourier transform. These demodulated signals are input to the frequency determination unit 4, where the codeword is determined from the frequencies f1, f2, etc., and output. The code word is, for example, FS
If the K signal is binary, it is 0 or 1 (1 bit),
If the FSK signal has four values, it is 00, 01, 10 or 11 (2 bits). If the FSK signal has eight values, it is 000, 001, 01.
0, 011, 100, 101, 110 or 111 (3 bits).

The frequency determination section 4 has a code word determination function corresponding to the number of bits of the FSK signal to be demodulated, so that it can support a demodulation circuit for a multi-level FSK signal. Therefore, in order to set the frequency to be determined according to the number of codewords, for example, the program of the CPU 2 is rewritten so that it can cope with a multi-level FSK signal.

[0011]

As described above, the F according to the present invention is used.
According to the SK signal demodulation circuit, the A / D converter and the CPU
Since the FSK signal is demodulated by a Fourier transform unit and a frequency determination unit, there is no need to use a multiplier that leads to an increase in the number of parts. Can be dealt with by rewriting the program, and the FSK signal receiver can be constructed economically.

[Brief description of the drawings]

FIG. 1 is a main block diagram of an embodiment of an FSK signal demodulation circuit according to the present invention.

FIG. 2 is an explanatory diagram of a Fourier transform.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D converter 2 CPU 3 Fourier conversion part 4 Frequency judgment part 5 Control part

Claims (4)

[Claims] 1. An A / D converter for sampling an FSK (Frequency Shift Keying) signal and converting it to a digital signal, an arithmetic circuit for converting a signal whose value changes with time from the A / D converter to frequency spectrum data, An FSK signal demodulation circuit comprising: a frequency determination unit that determines and outputs a codeword from a frequency of a signal from an arithmetic circuit. 2. The FSK signal demodulation circuit according to claim 1, wherein said operation circuit comprises a circuit for performing a Fourier transform operation. 3. The FSK signal demodulation circuit according to claim 1, wherein the frequency judgment unit has a code word judgment function corresponding to the number of bits of the FSK signal. 4. The frequency determining unit according to claim 1, wherein a program for determining a code word according to the number of bits of the FSK signal is rewritable.
The FSK signal demodulation circuit as described in the above.