Patent ID: 8229030

Claim:
A frequency shift keying (FSK) signal modulator comprising: a counter for receiving and counting information to be transmitted; and a threshold value decision circuit connected to an output of the counter for determining the output value of the counter with respect to a threshold value to transmit an output representative of a result of decision in the form of binary FSK signal, wherein said modulator determines a center frequency of an input modulation frequency component of an FSK demodulator connected with the modulator, a first and second frequencies of FSK signals respectively corresponding to binary information signals “0” and “1”, a symbol rate of modulation signal, and an input sampling frequency of the FSK demodulator, finds out first, second and third integer values corresponding with a ratio of center, first and second frequencies, and calculates a fourth integer value by dividing the input sampling frequency by the symbol rate and multiplying the divided result by the first integer, and wherein said counter decides whether or not the information to be transmitted (input data) is equal to “0”, and then, adds the second or third integer to a last count value obtained at one sampling period before when input data is equal to “0” or “1”, respectively, to hold the added result as a held count value obtained in the counter at a current sampling period, and further decides whether or not the held count value is greater than the fourth integer, and then, renews a current count value by subtracting the fourth integer from the held count value or by remaining the held count value when the held count value is greater than the fourth integer or equal to the fourth integer or less, respectively, said threshold value decision circuit decides whether or not the current count value is greater than a half of the fourth integer, and then, outputs a value of “0” or “1” as the binary FSK signal when the current count value is greater than a half of the fourth integer or equal to a half of the fourth integer or less, respectively.