FSK signal detector

1. An FSK signal detector comprising:

binarizing means for binarizing the amplitude of an input FSK signal;

a 2n-stage shift register comprised of 2n registers for sequentially shifting the FSK signal binarized by said binarizing means in response to a clock; and

adding means for calculating a sum of a total number of FSK signals having the value of “1” or “0” among FSK signals stored in a first to an n-th register of said 2n-stage shift register and a total number of FSK signals having the value of “0” or “1” among FSK signals stored in an (n+1)th to a 2n-th register.

2. An FSK signal detector according to claim 1 , further comprising:

amplitude limiting means disposed in front of said binarizing means for suppressing an amplitude fluctuation component of the input FSK signal.

3. An FSK signal detector according to claim 1 , further comprising:

FSK data generating means for generating FSK data based on a varying width when the sum calculated by said adding means varies in accordance with the clock supplied to said 2n-stage shift register.

4. An FSK signal detector according to claim 3 , wherein said FSK generating means includes:

subtracting means for subtracting n from the sum calculated by said adding means;

absolute value converting means for obtaining an absolute value of the output of said subtracting means;

a low pass filter for averaging the output of said absolute value converting means; and

comparing means for comparing the output of said low pass filter with a predetermined threshold to generate FSK data.

5. An FSK signal detector according to claim 3 , wherein said FSK generating means includes DC offset generating means, operative when the output of said low pass filter corresponds to a preamble added to the head of the FSK signal, for averaging an output corresponding to the preamble to generate a DC offset, and for holding the DC offset for a frame period of the FSK signal,

wherein said comparing means subtracts the DC offset generated by said DC offset generating means from the output of said low pass filter, and compares the difference with a threshold having the value of zero to generate the FSK data.

6. An FSK signal detector according to claim 5 , wherein said preamble is a spread code used in a spread spectrum communication.

7. An FSK signal detector according to claim 1 , wherein said clock supplied to said 2n-stage shift register has a frequency f CLK which is set to satisfy (f CLK /f IF− )−(f CLK /f IF+ )=8, where f IF− is the frequency of the FSK signal shifted in the negative direction, and f IF+ is the frequency of the FSK signal shifted in the positive direction, and the number 2n of stages of said 2n-stage shift register is set to an integer close to the frequency f CLK divided by the frequency f IF− .