Patent ID: 7026864

Claim:
A non-coherent frequency shift key demodulating circuit, comprising: an oversampling device, for receiving and examining an input digital non-coherent frequency shift key signal carrying a digital signal upon existence of transition, and further outputting a data bit signal recording whether a transition exists or not; a chain of registers, coupled to the oversampling device, receiving the data bit signal, and further counting and storing a quantity of logic high level status of the data bit signal received, and outputs a number-of-ones value signal correspondingly; a threshold device, coupled to the chain of registers, for receiving and comparing the number-of-ones value signal with a predetermined threshold value to determine the digital signal carried in the input digital non-coherent frequency shift key signal, wherein if the digital frequency shift key signal has a first frequency and a second frequency respectively representing a logic high level and a logic low level, the predetermined threshold value is determined as a quotient of a system data rate dividing a sum of the first frequency and the second frequency.