Phase locked loop for radio frequency receivers with digitally controlled frequency fine tuning has direct digital synthesizer giving an offset signal which is mixed

摘要

A phase-locked loop oscillator (1) for generating an output signal of desired frequency has a direct digital synthesizer (10) producing an offset signal which is mixed with the output signal to give a mixed frequency which is fed to a frequency divider. A phase-locked loop oscillator (1) for generating an output signal of desired frequency from a reference signal comprises a phase detector, charge pump (3), loop filter (4), voltage controlled oscillator (5) and a frequency divider in a return path. A direct digital synthesizer (10) produces an offset signal differentiated from the output frequency and these are mixed to give a mixed frequency which is fed to a frequency divider.