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Digital filter

  • US 6,002,297 A
  • Filed: 01/29/1998
  • Issued: 12/14/1999
  • Est. Priority Date: 08/02/1995
  • Status: Expired due to Fees
First Claim
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1. A frequency detection circuit comprising:

  • a first node to receive a first cyclical analogue signal at a first frequency (f1);

    frequency converter means to receive the first cyclical analogue signal, to convert the first signal to a converted frequency signal, and to supply the converted frequency signal to a digital filter (48) as a system clock signal for said filter;

    a second node to receive a second cyclical analogue signal at a second frequency (f2) which differs from the first frequency by a small amount;

    a delay circuit to delay the second signal by N cycles; and

    a subtractor to receive a current value of the second cyclical analogue signal (Sc) from the second node and a delayed value of the second cyclical analog signal (Sp) from the delay circuit, to subtract them and to provide any difference to the digital filter as a difference signal, whereby the digital filter provides an output signal comprising the second frequency (f2) and substantially suppressing any signal at the first frequency (f1).

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