Research And Design Of Low Phase Noise Frequency Synthesizer Based On Broadband VCO

With the development of science and technology, the requirements for the frequency source which providing the local oscillator reference signal for electronic test equipment have been getting higher and higher. Typically, the broadband low phase noise frequency source is based on the YTO. However, this frequency source has some inherent defects, such as slow speed of frequency switching, high power consumption and large volume. So it is desirable to be replaced by the VCO. Due to the broadband VCO’s low levels of phase noise, this article design on how to achieve a low phase noise frequency synthesizer based on broadband VCO.Firstly, by performing modeling analysis on the phase noise of PLL output signal and comparing the phase noise of the output signal between the VCO and YTO under the same reference and different loop bandwidths, conclude the design ideas of low phase noise frequency source based on broadband VCO which is extending the phase-locked loop bandwidth and using reference signal phase noise as the phase noise of the output signal.This frequency source system is mainly composed by reference module and low phase noise PLL module two parts. The main function of the reference module is providing a high frequency、low phase noise and small step signal for the post-stage circuit. And the low phase noise PLL module output the low phase noise signal by a new structure. In order to achieve their function, the reference module use the structure of DDS drive PLL and use a method to reduce the spurious signals which is provided by DDS. In the design of the low phase noise PLL, the article propose a new method used in the PLL’s feedback loop, by the method of using reference signal’s harmonic to mix with the output signal serial times can convert the narrowband reference input to wideband output signal. So, the system can output a low phase noise signal by extending the phase-locked loop bandwidth.Finally, complete the entire frequency source design and hardware circuit. By debugging and testing, this system can provide a 5GHz~10GHz signal which have 1Hz step, and this signal’s Phase noise and spurious suppression up to the standard.