A.V. Korolev1, Y.V. Korshikov2, S.G. Rykov3

1-3 «JSC All-Russian Scientific Research Institute of Radio Engineering» (Moscow, Russia)

A modern frequency synthesizer is a complex device designed to form oscillations and signals, while the level of phase noise of which, in the limiting case, should minimally exceed the phase noise of the reference oscillator, recalculated to the output frequencies. Hybrid synthesizers containing both analog and digital elements, including direct digital synthesizers (DDS), allow obtaining good results. Many possible structures of such frequency synthesizers are known, and therefore the problem arises of studying these structures with simultaneous estimation of the maximum achievable level of their phase noise.

In this article, a generalized block diagram of a hybrid frequency synthesizer is proposed. The influence of the DDS noise on the output noise of the frequency shift circuit (FSC) has been evaluated. It is shown that the advantage of a DDS based on frequency conversion over a circuit using DDS frequency images can reach 10-15 dB at offsets from the carrier frequency of tens of kHz, and this advantage will be the higher, the lower the phase noise of the reference oscillator. Formulas are proposed for calculating the frequency of the output oscillations of the DDS as part of the FSC, at which the deterioration of the phase noise does not exceed a given value. To check the correctness of the performed calculations, measurements were made of the phase noise FSC for two types of reference oscillator and the DDS. The discrepancy between the calculated and measured phase noise does not exceed 1-3 dB.

Korolev A.V., Korshikov Y.V., Rykov S.G. Hybrid synthesizer with two PLLs and DDS. Part 1. Frequency shift circuit. Radiotekhnika. 2023. V. 87. № 2. P. 178−192. DOI: https://doi.org/10.18127/j00338486-202302-21 (In Russian)

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