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US 5,345,236 AGranted
Improved sigma-delta type analog-to-digital converter and method
AssigneeHarris Corporation
InventorJohn Sramek, Jr.
Life of this patent
Estimating the term…
Abstract
A multiplexed sigma delta analog-to-digital (A/D) converter for low frequency applications has a single oversampling modulator together with a relatively high cutoff lowpass filter together with individual line frequency (50 or 60 Hz) rejection filters for each output channel.
Claims10
A multiplexed sigma delta analog-to-digital converter, comprising:
- (a) a sigma delta modulator with a modulator input and a modulator output;
- (b) an input multiplexer coupled between N signal inputs and said modulator input;
- (c) a digital filter coupled to said modulator output, said digital filter having a passband frequency of at least N times Fb, where Fb is a bandwidth for signals at said N signal inputs;
- (d) an output multiplexer coupled between said digital filter and N output filters;
- and
- (e) wherein said input and output multiplexers correlate said N output filters to said N signal inputs, and each one of said N output filters filters out a line frequency, Fline, where the frequency Fline is greater than Fb but less than N times Fb.
3 more elements
An analog-to-digital converter, said sampling converter
- (a) a sampling analog-to-digital converter, said sampling converter sampling at a rate of F;
- where F is an integer multiple of a frequency f.sub.noise and outputting a digital data stream;
- and
- (b) an averaging filter coupled to said sampling converter, said averaging filter averaging elements of said data stream corresponding to samplings of said sampling converter offset by a time equal to 1/(Nf.sub.noise) seconds;
- where N is a factor of said integer multiple.
2 more elements
A method of filtering the output of a sigma delta modulator, comprising the steps of:
- (a) applying an output stream from a sigma delta modulator to a low pass digital filter having a cutoff frequency greater than a frequency Fline where Fline is the frequency of a periodic noise source;
- and
- (b) averaging the outputs of said low pass digital filter at a rate which is N times the frequency, Fline, for integers of N greater than 1.
Dependencies are inferred from the claim text.