The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 26, 1976
Filed:
Jul. 18, 1975
Daniel Richard Asmussen, Kirkland, WA (US);
Tel-Tone Corporation, Kirkland, WA (US);
Abstract
An incoming signal (tone) and the feedback signal of a biquadratic filter are converted into square waves by zero crossing comparators. The phase state of the square waves is decoded and the decoded result is phase compared to determine if a 90.degree. phase shift exists between the incoming and feedback signals. If a 90.degree. phase shift does not exist, a counter is incremented or decremented, depending upon whether the phase comparison indicates that frequency of the incoming signal is greater, or less than the feedback signal. The output of the counter is decoded and utilized through a switching circuit to control the center frequency of the biquadratic filter (determined by the impedance of its feedback path). The switching circuit changes the impedance of the feedback path so that the center frequency is moved toward the frequency of the incoming signal. When the center frequency of the biquadratic filter is at the frequency of the incoming signal, the output of the frequency decoder provides a coded indication of the frequency of the incoming signal.