V.V. Romashov1, K.K. Khramov2, A.N. Doktorov3, K.A. Yakimenko4, N.A. Sochneva5

1-5 Murom branch of the Vladimir State University named after Alexander Grigoryevich
and Nikolai Grigoryevich Stoletov (Murom, Russia)

Digital signal synthesizers are used as signal generators in modern telecommunication and radar systems. They allow to generate the required signals with complex types of modulation and implement software control for the amplitude, frequency and instantaneous phase of the synthesized signal. This article shows the importance of high-speed digital-to-analog converters for improving the efficiency of direct digital synthesis of high-frequency signals in the higher Nyquist zones. Recovery modes RFZ3, RFZ4, with doubling of bipolar pulses at the output of a high-speed digital-to-analog converter are proposed. The envelopes of the spectra of the studied modes of high-speed DACs are calculated, a comparison is made with the envelopes of the existing operating modes NRZ, RZ, RF, RFZ and RFZ2. The values of dimensionless quantities showing the change in amplitude from frequency for the modes under consideration relative to the main mode of operation of NRZ are obtained.  A model of a high-speed digital-to-analog converter with the proposed operating modes in the MATLAB Simulink program has been compiled and investigated. By means of mathematical modeling, the realizations of the output signal of high-speed digital-analog converters with the studied special modes of operation in the time and frequency domains are obtained. Linear frequency modulation is introduced to demonstrate the envelope of the spectrum. It is revealed that the recovery modes RFZ3, RFZ4 of high-speed digital-to-analog converters allow increasing the amplitude of harmonics of fundamental frequency images in the eighth and ninth Nyquist zones to 20 and 15 dB, respectively, relative to the envelope of the spectrum of the main operating mode NRZ. In addition, the efficiency of the RFZ4 mode is shown in the synthesis of signals at frequencies of images with the number n = -5… 5 in the tenth and eleventh Nyquist zones with an increase in the amplitude of harmonics up to 20 dB or more, depending on the value of the synthesized fundamental frequency. The use of higher Nyquist zones for direct digital synthesis makes it possible to significantly, tenfold or more, increase the output frequency of a digital computing synthesizer, and the use of special operating modes of high-speed DACs increases the amplitude of harmonics of fundamental frequency images.

Romashov V.V., Khramov K.K., Doktorov A.N., Yakimenko K.A., Sochneva N.A. Improving the efficiency of the use of higher Nyquist zones in direct digital synthesis of high-frequency signals. Radiotekhnika. 2022. V. 86. № 5. P. 135−144. DOI: https://doi.org/10.18127/j00338486-202205-16 (In Russian)

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