Demodulating frequency shift keying modulated input signal
First Claim
1. A method of demodulating a frequency shift keying (FSK) modulated input signal whose frequency varies between a first frequency and a second frequency, the method comprising:
- providing a first signal based on the FSK modulated input signal, and a second signal having a delay relative to the first signal greater than a plurality of cycles of the lesser of the first and second frequencies;
providing a succession of phase reference signals having respective incrementally greater phase delays relative to the first signal;
providing samples of the phase reference signals at intervals determined by the second signal; and
detecting a transition between the first and second frequencies when the relative values of the samples vary during a first plurality of intervals and then remain constant during a second plurality of intervals.
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Abstract
A method of demodulating an FSK modulated input signal whose frequency varies between first and second frequencies. The input signal is delayed by a plurality of cycles, providing a second signal. A succession of phase reference signals having respective incrementally greater phase delays relative to the input signal are provided. Samples of the phase reference signals are taken at intervals determined by the second signal. A transition between the first and second frequencies is detected when the relative values of the samples of the phase reference signals remain constant during a plurality of intervals after varying. A high speed clock is not required to perform the demodulation.
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Citations
8 Claims
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1. A method of demodulating a frequency shift keying (FSK) modulated input signal whose frequency varies between a first frequency and a second frequency, the method comprising:
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providing a first signal based on the FSK modulated input signal, and a second signal having a delay relative to the first signal greater than a plurality of cycles of the lesser of the first and second frequencies; providing a succession of phase reference signals having respective incrementally greater phase delays relative to the first signal; providing samples of the phase reference signals at intervals determined by the second signal; and detecting a transition between the first and second frequencies when the relative values of the samples vary during a first plurality of intervals and then remain constant during a second plurality of intervals. - View Dependent Claims (2, 3, 4)
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5. A method of demodulating a frequency shift keying (FSK) modulated first signal whose frequency varies between at least a first frequency and a second frequency, the method comprising:
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providing a second signal having a delay relative to the first signal greater than a plurality of cycles of the lesser of the first and second frequencies; providing a succession of phase reference signals having respective incrementally greater phase delays relative to the first signal; providing samples of the phase reference signals at intervals determined by the second signal; and detecting a transition between the first and second frequencies when the relative values of the samples vary during a first plurality of intervals and then remain constant during a second plurality of intervals. - View Dependent Claims (6, 7, 8)
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Specification