We present an oscillator design based on stacked-FET for high power terahertz signal generation in CMOS technologies. This design addresses the challenges commonly encountered in conventional high-power oscillators. These challenges include low inductor quality factor (Q) associated with the use of large active devices, and the need for extensive chip area when combining multiple optimally-designed cells. Based on a Π-embedded oscillator architecture, we show that, with N-stacked FET, the optimal embedding inductor and load resistance increase approximately with N. This contrasts with the traditional size scaling approach, where L and R decreases unfavorably as the device size increases. We take advantage of this characteristic, by proposing a design methodology that simultaneously achieves high output power and optimal inductor Q. The concept is validated by a design example of a two-stacked Π-embedded oscillator operating at 180 GHz and fabricated in 45-nm CMOS SOI, delivering 11 dBm RF power from two losslessly combined oscillator cores. This design demonstrates the highest output power among CMOS oscillators at this frequency.

This paper reports an approach to designing compact high efficiency millimeter-wave fundamental oscillators operating above the fmax=2 of the active device. The approach takes full consideration of the nonlinearity of the active device and the finite quality factor of the passive devices to provide an accurate and optimal oscillator design in terms of the output power and efficiency. The 213-GHz single-ended and differential fundamental oscillators in 65-nm CMOS technology are presented to demonstrate the effectiveness of the proposed method. Using a compact capacitive transformer design, the single-ended oscillator achieves 0.79-mW output power per transistor (16 μm) at 1.0-V supply and a peak dc-to-RF efficiency of 8.02% (VDD=0.80 V) within a core area of 0.0101mm2, and the measured phase noise is -93:4 dBc/Hz at 1-MHz offset. The differential oscillator exhibits approximately the same performance. A 213-GHz fundamental voltage-controlled oscillator (VCO) with bulk tuning method is also developed in this work. The measured peak efficiency of the VCO is 6.02% with a tuning rang of 2.3% at 0.6-V supply.