A quad-core 15GHz BiCMOS VCO with −124dBc/Hz phase noise at 1MHz offset, −189dBc/Hz FOM, and robust to multimode concurrent oscillations

The relentless development of next-generation communication and radar systems sets increasingly stringent requirements on the spectral purity of local oscillators. Decreasing phase noise is crucial to support efficient modulation formats with large symbol constellations, as well as to enable innovative radar applications, e.g., anti-collision, gesture recognition, and medical imaging. To minimize phase noise, bipolar transistors offer some advantages over ultra-scaled CMOS: higher supply voltage (thus larger oscillation amplitudes), lower 1/f noise, higher-Q passives (due to higher resistivity substrate and, possibly, thicker metals), and higher f
_T
, f
_max
for a given technology node, which results in a cost advantage for a variety of medium-volume applications (e.g., infrastructure transceivers). For a given supply voltage, a tank showing a smaller resistance at resonance yields lower phase noise. As a result, the minimum phase noise achievable by a single voltage-controlled oscillator (VCO) is ultimately bounded by the smaller realizable inductor displaying the highest Q. To achieve significantly lower phase noise levels, bilaterally coupling N oscillators [1-3] is a viable option. However, to fully preserve the 10log(N) phase-noise advantage, while avoiding undesired multi-tone concurrent oscillations, the coupling network must be carefully designed. This work presents a quad-core bipolar VCO achieving phase noise as low as -124dBc/Hz at 1MHz offset from the 15GHz carrier, -189dBc/Hz figure-of-merit (FOM), and 16% tuning range. Insights are given into the design of the resistive network employed to couple the four oscillators, a key element in achieving the reported performance.