Frequency and Power Scaling in mm-Wave Colpitts Oscillators

The maximum oscillation frequency depends on the oscillator topology and the loss of oscillator's active and passive components. The oscillator phase noise, and hence the oscillator figure-of-merit (FOM), degrades much faster than the wellknown low-frequency expressions as the oscillation frequency reaches the maximum oscillation frequency. This paper covers the analysis and design of Colpitts oscillators with the best possible phase noise as the oscillation frequency approaches the maximum oscillation frequency while predicting the degradation in FOM. Experimental results corresponding to proof-of-concept differential Colpitts oscillator prototypes at 106 and 148 GHz that use a resonant biasing scheme to reduce phase noise, implemented in a 130-nm SiGe HBT BiCMOS technology, are presented. Ideally, the oscillator phase noise at a given frequency can be reduced by increasing the power consumption, while appropriately scaling the oscillator components. Such power scaling cannot be done indefinitely as it leads to impractical passive component values. Coupling identical oscillators is an alternate approach to enhance the phase noise. In this paper, a common-mode coupling scheme is introduced as a robust technique in reducing phase noise in millimeter wave frequencies. Experimental results of a 106-GHz 8-element common-mode coupled Colpitts oscillator, implemented in a 130-nm SiGe HBT BiCMOS technology, with a measured phase noise of -111 dBc/Hz at 1-MHz offset while consuming 90 mW are presented.