A 28.7-/57.4-GHz Dual-Mode Dual-Band Ring Oscillator With Controllable Second Harmonic

In this paper, a concurrent dual-band four-stage ring oscillator topology is presented. The proposed design is considered as a special case of cross-coupled oscillator equivalent under the unbalanced and balanced topology scenarios. Thereby, providing an useful insight into the multi-stage ring oscillator analysis at the startup and the steady state oscillation conditions. The proposed topology supports amplitude control of the second harmonic oscillation based on bias condition of the low noise transistors that eventually switch between the single-tone fundamental oscillation mode and the concurrent dual-band oscillation mode. In this work, it is also experimentally verified that the proposed dual-band oscillator has enhanced performance for both the frequency bands with a phase noise of –106.1 dBc/Hz at 28.7 GHz and –102.8 dBc/Hz at 57.4 GHz measured at 1 MHz offset with a wideband spectral purity. The oscillator is fabricated in a 0.18 μm SiGe BiCMOS process consuming 17.4 mW dc power from a 1.8 V supply voltage and occupying a core die area of 0.096 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>.