Novel Phase-Continuous Frequency Hopping Control for a Direct Frequency Synthesizer Using a Quadrature Mixer Driven by Two DDSs

Abstract

This paper presents novel phase-continuous frequency hopping (FH) control for a direct frequency synthesizer (DFS) using a quadrature mixer driven by two direct digital synthesizers (DDSs). To achieve wideband FH in both of the lower and the upper sidebands of a local frequency in a quadrature mixer, the proposed DFS decreases or increases the phase of DDS output signals corresponding to frequency offset from a local frequency of the quadrature mixer. To realize phase decrement, the proposed method adds a complement number in a phase accumulator of a DDS, while a conventional DDS does not use phase decrement but uses a switchable combiner. In addition, as the phase accumulator output changes continuously by summing phase increment, the proposed method always assures phase continuity of a DFS output signal, which ends up suppressing sidelobe level of frequency hopped signals. The calculation and measurement results indicate that a sidelobe of a signal spectrum using the proposed phase continuous method is approximately 10 dB better than that using a conventional phase discontinuous method.