Circuit for digital FM demodulation
AssigneeITT Industries, Inc.
InventorRobert Smith
Life of this patent
Estimating the term…
Abstract
A digital FM demodulation circuit provides improved resolution by selecting from a group of at least four of the most recent samples, a subgroup of three samples. The first and last samples of the selected subgroup are summed and the sum is divided by the intermediate sample.
Claims16
A demodulation circuit for frequency modulated (FM) signals comprising:
- first means for receiving an analog FM signal and for periodically generating at a predetermined sampling rate samples of said analog FM signal in digital signal representation;
- means for comparing a first sample of from at least four sequentially occuring ones of said samples with a second sample of said at least four sequentially occuring samples;
- means responsive to said comparing means for selecting a group of samples from said at least four sequentially occuring samples, said selected group comprising a first group of three samples when said first sample has a first predetermined relationship to said second sample and said selected group comprising a second group of three samples when said first sample has a second predetermined relationship to said second sample;
- and
- means for generating digital signal representations of the demodulated FM signal by utilizing said selected group of samples.
A demodulation circuit for providing digital output signals representative of a demodulated analog FM signal from samples of said analog FM signal, where each of said samples is a digital signal representation, said samples occuring at a predetermined rate, said circuit comprising:
- means for comparing a first sample from a group of sequentially occuring samples to a second sample from said group;
- means responsive to said comparing means for selecting a subgroup of samples from said group;
- and
- means for generating said digital output signals from said selected subgroup.
A circuit for the digital FM demodulation of temporally equidistant samples derived from an analog frequency modulated (FM) signal by way of sampling with the aid of a sampling signal, said circuit comprising:
- a chain of serially connected delay stages for receiving said sample, said chain comprising a first delay stage, a middle delay stage and a third delay stage, each delay stage delaying said samples by the period of said sampling signal;
- a comparator having a minuend input coupled to the input of said middle stage, a subtrahend input coupled to the output of said middle stage, and an output;
- first, second, and third switching means each having first and second inputs, an output and a control input, said control input of all of said switching means being coupled to said comparator output, said first inputs of said first, second, and third switching means being coupled to the inputs of said first, middle and third delay stages, respectively, said second inputs of said first, second and third switching means being coupled to the outputs of said first, middle, and third switching means, respectively;
- an adder having a first input coupled to said first switching means output, a second input coupled to said third switching means output, and a sum output;
- a divider having a dividend input coupled to said sum output, and a divisor input coupled to said third switch means output, and an output for providing a digital demodulated signal output.
Dependencies are inferred from the claim text.