Design and Implementation of Integer-N Frequency Synthesizer for Radiometer

This paper presents the design and implementation of an integer-N frequency synthesizer for a radiometer. The proposed design has the ability to achieve high spectral purity and effective spur cancellation, which leads to improve the output spectrum of the radiometer. The spectral purity, effective spur cancellation and harmonic level suppression are achieved by incorporating filters in the chain of Local Oscillators (LOs). The architecture of the proposed Integer-N frequency synthesizer design consists of CMOS-based Integrated Circuits (ICs) and can generate three distinct stable LO signals of 1.25 GHz, 2.5 GHz and 9.1 GHz for the radiometer receiver. The proposed synthesizer architecture is simulated by using multiple software platforms; Loop filter has been analyzed in ADIsimPLL software from Analog Devices; Synthesizer RF chain has been design in Advanced Design System (ADS); whereas, its schematics and PCB are designed in Altium Designer software. We tested our proposed synthesizer design successfully at all three frequencies and showed that the LO1 achieved phase noise up to -90 dBc@10 kHz, LO2 achieved phase noise up to -100 dBc@10 kHz, and LO3 achieved phase noise up to -105 dBc@10 kHz. We analyzed the link budgeting of each LO to meet the power requirements of downconverters. Moreover, we also carried out the performance analysis of our proposed design among fractional-N synthesizer design in terms of spectral purity and spur levels. The results show that the proposed synthesizer has spur and harmonic free LO signals compared to the fractional-N synthesizer design.