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:
Dec. 06, 1977
Filed:
Oct. 20, 1975
Andrew M Walker, Gaithersburg, MD (US);
Ova Gene Gabbard, Germantown, MD (US);
Digital Communications Corporation, Gaithersburg, MD (US);
Abstract
A phase locked loop with pre-set and squelch capability particularly adapted for burst type signals. In addition to the conventional phase detector, loop filter (LF) and voltage controlled oscillator (VCO) the loop includes a squelch switch connected between the phase detector and LF. A track and hold circuit is connected in series with another switch between output and input of the LF. Both switches and the track and hold circuit itself are controlled by the output of a level detector which indicates presence of an intermittent (i.e., bursty) carrier. The squelch switch is closed, connecting the phase detector to the LF, when the output of the level detector indicates the presence of a carrier burst. At the same time, the second switch is opened so that the LF is not affected by the output of the track and hold circuit. In addition, the track and hold circuit is enabled to track the error voltage output of the LF. At the conclusion of a burst the squelch switch is opened so that the noisy output of the phase detector will not affect the LF. In addition, the second switch is closed to allow the output of the track and hold circuit to reach the LF and finally, the track and hold circuit holds the previous error voltage output of the LF. Thus the error voltage, at the conclusion of the carrier burst, is provided by the track and hold circuit to the LF to maintain the VCO at the last known carrier frequency.