Programmable-step, high-resolution frequency synthesizer which substantially eliminates spurious frequencies without adversely affecting phase noise

摘要

A frequency synthesizer is described which operates over a wide frequency range at high resolution and variable step size without trading off between spurious frequency rejection and phase noise suppression. The synthesizer includes a magnetically-turned YIG oscillator which generates a desired output frequency from a received tuning signal. The output signal is fed back into a phase locked loop which generates the tuning signal. The phase locked loop includes a harmonic mixer for mixing the output signal with a reference frequency F. sub.2. The mixer receives a base frequency signal and a harmonic select signal resulting in the generation of the reference signal, F.sub.2. The mixed signal is input to a programmable divider, then to a phase detector which receives another reference signal, F.sub.1. The phase detector output is the tuning signal which is coupled to the YIG oscillator. Both reference frequencies, F.sub. 1 and F.sub.2, are derived from a common base frequency. A base frequency source includes a voltage-controller oscillator coupled to another phase locked loop. This other phase locked loop receives two reference signals, F.sub.x and F.sub.y. Reference F.sub. x preferably is generated by a direct digital synthesizer that receives programmable tuning parameters. Reference F.sub.y may be generated with a fixed, switched or other frequency source. A microprocessor is included for selecting the programmable divider factors, the direct digital synthesizer tuning parameters, and other variable factors.