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A SiGe fractional-N frequency synthesizer for mm-wave wideband FMCW radar transceivers

: Hasenaecker, G.; Delden, M. van; Jaeschke, T.; Pohl, N.; Aufinger, K.; Musch, T.


IEEE transactions on microwave theory and techniques 64 (2016), No.3, pp.847-858
ISSN: 0018-9480
Journal Article
Fraunhofer FHR ()

A millimeter-wave (mm-wave) frequency synthesizer is presented focusing on an ultra-high-speed fractional-N frequency divider and a highly linear phase-frequency detector (PFD). All circuits are integrated into a high-frequency SiGe bipolar technology. The programmable frequency divider can be operated at input frequencies between dc and 57 GHz for division factors in the entire integer range from 12 to 259. The PFD is optimized for fractional-N synthesis, which requires an extremely linear characteristic due to the modulation of its input frequency. The frequency divider and the PFD are used together with an 80-GHz wideband voltage-controlled oscillator (VCO) and transceiver for a high precision mm-wave frequency-modulated continuous-wave (FMCW) radar sensor. As shown by the experimental results the realized circuits stabilize the mm-wave VCO with an extremely low phase noise below -97 dBc/Hz at 10-kHz offset around its center frequency of 80 GHz and can generate a highly linear frequency ramp with a bandwidth of 24 GHz. Furthermore, the accuracy of the synthesizer is demonstrated by FMCW radar distance measurements inside a waveguide and in free space. Inside the waveguide a standard deviation of the phase of the target below 0.0018 degrees (which corresponds to 9.4 nm) was measured.