Patent ID: 6658241
Filing Date: 2003-12-02
Classification: H03J

Abstract:
Automatic frequency control apparatus suitable for use in a radio receiver of a carrier signal including an error which shifts the frequency of the carrier signal relative to a first reference frequency, said carrier signal being modulated by a baseband signal containing information to be detected, said information being required to lie within an allowed frequency range, said apparatus comprising in combination:a converter responsive to said carrier signal to generate a residual carrier signal modulated by said baseband signal, said residual carrier signal having a residual frequency range within said allowed frequency range; a frequency shifter responsive to a control signal to shift the frequency of said residual carrier signal to generate a frequency shifted signal; a frequency detector responsive to any frequency error in said frequency shifted signal relative to a second reference frequency to generate said control signal whereby said frequency error in said frequency shifted signal is reduced; an information detector arranged to detect said information from said frequency shifted signal; and a filter arranged to filter said frequency shifted signal.