Frequency demodulator with resampled output
First Claim
1. An FM demodulator comprising:
- an analog-to-digital converter (ADC) for receiving an FM signal and producing FM samples;
a demodulator processor connected to said ADC for receiving said FM samples and producing FM output, said demodulator processor including;
edge detector, said edge detector receiving said FM samples and producing pulses;
counter, connected to said edge detector, said counter producing a measured cycle period based on said pulses from said edge detector;
first register connected to said counter, said first register producing a demodulated output based on said measured cycle period from said counter;
second register connected to said first register, said second register producing a resampled output based on said demodulated output from said first register.
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Abstract
An receiver receives, amplifies, filters, and downconverts an RF signal to obtain an FM signal. The FM signal is then limited by a limiter and sampled by an ADC. The FM samples from the ADC are provided to an edge detector which detects transitions in the FM samples. The transitions correspond to zero crossings in the FM signal. The time period between the zero crossings, or the cycle width, is measured with a counter to determine the instantaneous frequency fc of the FM signal. The demodulated output is proportional to the instantaneous frequency which can be determined from the measured cycle periods as fc =1/2Tc, fc ≈-αTc, or fc ∝Tc, where Tc is the measured cycle period, and α is a constant based on the slope of 1/2Tc,avg, where Tc,avg is the average cycle period. The sample rate of the demodulated output can be reduced, through resampling, to minimize power consumption in the subsequent signal processing blocks.
37 Citations
12 Claims
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1. An FM demodulator comprising:
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an analog-to-digital converter (ADC) for receiving an FM signal and producing FM samples; a demodulator processor connected to said ADC for receiving said FM samples and producing FM output, said demodulator processor including; edge detector, said edge detector receiving said FM samples and producing pulses; counter, connected to said edge detector, said counter producing a measured cycle period based on said pulses from said edge detector; first register connected to said counter, said first register producing a demodulated output based on said measured cycle period from said counter; second register connected to said first register, said second register producing a resampled output based on said demodulated output from said first register. - View Dependent Claims (2, 3)
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4. A method for demodulating an FM signal comprising the steps of:
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sampling said FM signals with an analog-to-digital converter (ADC) to produce FM samples; detecting transmissions in said FM samples; measuring cycle periods based on said detection of transition in said FM samples; latching said measured cycle periods to produce a demodulated output; resampling said demodulated output to produce a resampled output; calculating an FM output based on said measured cycle periods based on said demodulated output and said resampled output. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12)
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Specification