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:
Feb. 05, 1991
Filed:
Jan. 11, 1988
Walter H Kehler, Jr, Sunrise, FL (US);
Motorola, Inc., Schaumburg, IL (US);
Abstract
The period of time that the squelch circuit maintains a radio receiver's audio amplifier active after the signal strength of a received carrier fades below a threshold level is inversely proportional to the strength of the received carrier immediately before the fade. This threshold level is also variable. If, immediately before the fade, the received signal strength exceeds a predetermined trigger level (Vtrg) the threshold level is raised. A buffer amplifier (102) charges a capacitor (C) to a voltage which is proportional to the strength of a received carrier. If the carrier fades below a threshold (Vth2 or Vth3, the buffer is disabled and the capacitor slowly discharges through a resistor (R). When the voltage at the capacitor crosses a reference voltage (Vref1) the output of a comparator (104) switches, thereby deactivating the receiver's audio amplifier. If the voltage at the buffer output is within a specified range, a feedback control circuit (112) switches a variable hysteresis feedback circuit (110) such that the negative-going threshold of the comparator (106) is switched from one threshold level (Vth2) to another (Vth3).