Frequency demodulator and method for asynchronously demodulating sample signals
First Claim
Patent Images
1. In a digital frequency demodulator that includes an analog-to-digital converter for sampling a frequency-modulated input signal at regular time intervals, to produce a sequence of samples, wherein the input signal deviates about a mean, a method comprising the steps of:
- comparing each sample with its immediately preceding sample and determining when the samples have opposite polarities relative to the mean;
interpolating between each successive pair of samples determined in the step of comparing to have different polarities, to estimate the time at which the input signal corresponds to the mean;
determining the time duration between successive time estimates estimated in the step of interpolating;
calculating the frequency of the input signal based on the time durations determined in the step of determining.
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Abstract
An improved digital frequency demodulator and method for demodulating a sampled asynchronous FM input signal that determines the time duration of each successive half cycle by counting the number of successive samples of the same polarity and by interpolating between the samples immediately before and immediately after the detected zero crossings at the beginning and the end of each half cycle.
17 Citations
7 Claims
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1. In a digital frequency demodulator that includes an analog-to-digital converter for sampling a frequency-modulated input signal at regular time intervals, to produce a sequence of samples, wherein the input signal deviates about a mean, a method comprising the steps of:
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comparing each sample with its immediately preceding sample and determining when the samples have opposite polarities relative to the mean; interpolating between each successive pair of samples determined in the step of comparing to have different polarities, to estimate the time at which the input signal corresponds to the mean; determining the time duration between successive time estimates estimated in the step of interpolating; calculating the frequency of the input signal based on the time durations determined in the step of determining. - View Dependent Claims (2, 3, 4)
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5. A digital frequency demodulator comprising:
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an analog-to-digital converter for sampling a frequency-modulated input signal at regular time intervals, to produce a sequence of samples, the input signal deviating about a predetermined mean; a comparator for comparing each sample with its immediately preceding sample, to determine when the samples have opposite polarities relative to the mean; an interpolator for examining each successive pair of samples determined by the comparator to have opposite polarities relative to the mean, to estimate the particular time at which the input signal corresponds to the mean; and a processor for determining the time duration between successive time estimates estimated by the interpolator, which represents the time durations of the successive half cycles of the input signal, and for updating a calculation of the input signal'"'"'s frequency. - View Dependent Claims (6)
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7. A digital frequency demodulator comprising:
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an analog-to-digital converter for sampling a frequency-modulated input signal at regular time intervals, to produce a sequence of samples, the input signal deviating about a predetermined mean; a comparator for comparing each sample with its immediately preceding sample, to determine when the samples have opposite polarities relative to the mean, and thus the particular sample period during which the input signal crosses through the mean; and a processor for determining the time durations between successive mean crossings of the input signal, according to the following formula for the nth half cycle;
space="preserve" listing-type="equation">Time Duration, t=Δ
.sub.first +NT+Δ
t.sub.lastwhere; N=No. of samples of same polarity during nth half cycle, Time period between successive samples, ##EQU6## Afirst =First sample of nth half cycle, Aprev =Sample previous to Afirst, Alast =Last sample of nth half cycle, Anext =Sample after Alast ; wherein the processor further is configured to repeatedly update a calculation of the input signal'"'"'s frequency based on the successive half-cycle time duration determinations.
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Specification