FSK signal modulator for producing a binary FSK signal

Abstract

An FSK signal modulator is provided in a transmitter which receives desired information to be transmitted on its input and which modulates the information to be transmitted to transmit a binary FSK signal. A counter counts a value of addition with the value of addition modified in accordance with a predetermined rule, depending on the value specified by the information to be transmitted, and for holding the counted value. The count value is determined by a threshold value decision circuit with respect to a threshold value. The result from the decision is output in the form of binary FSK signal. An FSK signal modulator will be provided which is simplified in circuit constitution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic block diagram showing a transmitter and a receiver, the transmitter being provided with a binary FSK signal modulator embodying the present invention;

FIG. 2 is a flowchart useful for understanding the operation of the FSK signal modulator; and

FIG. 3 is a schematic block diagram showing an example of a conventional FSK modulator.

Claims

1. A frequency shift keying (FSK) signal modulator for receiving information to be transmitted to produce an FSK signal, comprising: a counter for counting a value of addition with the value of addition modified in accordance with a predetermined rule, depending on the value specified by the information to be transmitted, and for holding the counted value; anda decision circuit for comparing the count value to a threshold value for decision and for producing a binary FSK signal which is in keeping with a result of the decision.

2. The FSK signal modulator in accordance with claim 1, wherein, when the count value has exceeded a predetermined value, said counter subtracts the predetermined value from the count value.

3. The FSK signal modulator in accordance with claim 1, wherein the count values are positive integers not less than there, out of the count values that can be taken by said counter, a predetermined half plurality of consecutive count values being allotted to one of binary values “1” and “0” of one-bit information, while a remaining half plurality of consecutive count values are allotted to another of the values “1” and “0” of the one-bit of information.

4. The FSK signal modulator in accordance with claim 1, wherein, when a relationship of a center frequency of a modulation frequency component, a frequency of an FSK signal corresponding to “0” of the information to be transmitted and a frequency of an FSK signal corresponding to “1” of the information to be transmitted is defined by three smallest proportional integers as a first number, a second number and a third number, respectively, said counter adds the second and third numbers as indicating the frequencies of an FSK signal corresponding to the information signal “0” and “1”, respectively, to the count value to increment said counter.

5. The FSK signal modulator in accordance with claim 4, wherein said counter is structured such that a fourth value obtained by dividing a sampling frequency for the FSK signal by a symbol rate of a modulation signal and multiplying a value resultant from a division by the first number is used as a number of values that can be taken by said counter.

6. A method of receiving information to be transmitted to produce a frequency shift keying (FSK) signal, comprising: a count step of counting a value of addition with the value of addition modified in accordance with a predetermined rule, depending on a value specified by the information to be transmitted, and for holding the counted value; anda decision step of comparing the count value to a threshold value for decision and of producing a binary FSK signal which is in keeping with a result of decision.

7. The method in accordance with claim 6, wherein, when the count value has exceeded a predetermined value, said count step subtracts the predetermined value from the count value.

8. The method in accordance with claim 6, wherein the count values are a positive integer not less than three, out of the count values that can be taken by said count step, in said decision step, a predetermined half plurality of consecutive count values are allotted to one of “1” and “0” of one-bit information, while a remaining half plurality of consecutive count values are allotted to another of “1” and “0” of the one-bit information.

9. The method in accordance with claim 6, wherein, when a relationship of a center frequency of a modulation frequency component, a frequency of an FSK signal corresponding to “0” of the information to be transmitted and a frequency of an FSK signal corresponding to “1” of the information to be transmitted is defined by three smallest proportional integers as a first number, a second number and a third number, respectively, said count step adds the second and third numbers as indicating the frequencies of an FSK signal corresponding to the information signal “0” and “1”, respectively, to the count value to increment the count value.

10. The method in accordance with claim 9, wherein a fourth value obtained by dividing the sampling frequency for the FSK signal by a symbol rate of a modulation signal and multiplying a value resultant from a division by the first number is used as a number of values that can be taken in said count step.