34.6 A 47.3-to-58.4GHz Differential Quasi-Class-E Colpitts Oscillator Achieving 198.8dBc/Hz FoMT

The increasing demand for complex modulation schemes to achieve high data-rates in millimeter-wave (mm-wave) communication systems necessitates local-oscillation (LO) signals with exceptionally high spectral purity. As mm-wave voltage-controlled oscillators (VCOs) suffer from limited performance, many existing solutions for mm-wave LO generation rely on harmonic extraction from a low-frequency VCO [1]. However, additional power-hungry and area-consuming amplification stages are usually required owing to the weak harmonic components. Alternatively, recent research has extensively explored multi-core fundamental VCO topologies [2]. By coupling N identical oscillators, phase noise theoretically improves by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10\log_{10}(\mathsf{N})$</tex> compared to individual cores. Meanwhile, the a-factor degradation caused by the so-called “small-inductor” problem in mm-wave oscillator designs can be alleviated. Despite the superior phase noise offered by both harmonic-extraction and multi-core-coupling configurations, the peak FoM and FoMT achieved are only up to 190.3 and 191.6dBc/Hz at a 10MHz offset in the 50 to 60GHz frequency range, which are approximately 5 to 10dB lower than their low-frequency counterparts. Two such prior-art LO generators [1], [2] are illustrated and summarized in Fig. 34.6.1. To address these performance limitations, this paper proposes a mm-wave Quasi-Class-E Colpitts (QCEC) oscillator, as shown in Fig. 34.6.1. It features a transformer-based two-port resonance, enabling high-frequency fundamental oscillation, waveform shaping for power efficiency enhancement, and phase-noise suppression. A QCEC oscillator prototyped in a 40nm CMOS process achieves a 47.3-to-58.4GHz frequency tuning range (FTR) and -124.9 to -119.8dBc/Hz phase noise at a 10MHz offset, resulting in peak FoM and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathsf{FoM}_{\mathsf{T}}$</tex> of 192.3dBc/Hz and 198.8dBc/Hz, respectively.