Comparison of inductor types for phase noise optimized oscillators in SiGe at 34 GHz

In this paper two integrated auxiliary VCOs working at a center frequency of 34 GHz for use in a 240 GHz transceiver chip in SiGe technology for ultra-wideband radar applications are presented. The oscillators are using different realizations of the resonator inductance which are compared in terms of quality factor and their influence on the phase noise of the resulting oscillator output signal. The improvement in quality factor at a frequency of 34 GHz between the oscillator using microstrip transmission lines and the oscillator using spiral inductors is simulated to be around 76 % which causes a simulated absolute improvement in output signal phase noise of around 4.5 dB. Both oscillators are realized as test circuits with which the difference can be measured to be around 5 dB proving the advantage of spiral inductors in terms of quality factor for frequencies around 34 GHz resulting in an integrated VCO design providing a low phase noise of -107 dBc/Hz @ 1 MHz offset and a wide tuning range of 6.78 GHz.