An X-band broadband fast settling frequency synthesizer

To achieve fast settling time and low spurs, an integrative design method is proposed, which adopts the ideas of super-high frequency phase and frequency detection, large loop bandwidth and systematic DDS frequency planning. An X-band high performance broadband frequency synthesizer with feature of ultra fast settling speed has been developed. The structure of the frequency synthesizer is direct digital synthesizer (DDS) plus fast lock phase lock loop (FL-PLL) and the output band of the frequency synthesizer is 1 GHz (from 10.5 GHz to 11.5 GHz). Test results show that, under the condition of 1 GHz frequency hopping, the developed frequency synthesizer has the following features: positive settling time is 0.42 μs and the negative settling time is 0.30 μs, the SFDR is -61.3 dBc, the phase noise is -100 dBc/Hz@1 kHz offset and the minimum frequency hopping step is 12 Hz.