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Efficient cancelling of AC line interference in electronic instrumentation

  • US 5,278,777 A
  • Filed: 10/10/1989
  • Issued: 01/11/1994
  • Est. Priority Date: 10/10/1989
  • Status: Expired due to Fees
First Claim
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1. In an electrical instrument having a source of a low level input signal which is amplified, converted to digital data and presented in a digital signal processor to provide an output signal, and wherein the input signal is contaminated by periodic noise components of substantially constant frequency, the improvement comprising:

  • (a) means in the digital signal processor for estimating a noise component ni (k) at the sample k in the sampled input signal x(k) at the sample k in accordance with the expression;

    
    
    space="preserve" listing-type="equation">n.sub.i (k)=a.sub.i cos[2τ

    (f.sub.0 /f.sub.s)k]+b.sub.i sin[2τ

    (f.sub.0 /f.sub.s)k] where ni (k) is the estimator of the noise component ni (i), f0 is the frequency of the interference noise component, fs is the sampling frequency at which the input signal is converted to digital data, and the coefficients ai and bi are recalculated for the sinusoidal component in the periodic noise at each time point j using the recursion relationships;

    ##EQU3## where ai (0)=bi (0)=0; and

    (b) means in the digital signal processor for subtracting the noise estimator ni (k) at the sample k from the input signal x(k) to yield an output signal from which the noise component has been substantially cancelled.

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