Analysis and Design of Transformer-Based Dual-Band VCO for Software-Defined Radios

This work presents complete analysis of both one- port and two-port dual-band oscillators using transformer-based fourth-order LC tanks, from which critical parameters including oscillation frequency, start-up condition, tank Q, phase noise-are thoroughly derived and compared. It is shown that one-port oscillators consume less power than two-port counterparts but may suffer from stability problem which can be solved by a notch-peak cancellation technique. On the other hand, compared to one-port oscillators, two-port oscillators need to consume more power to obtain the same output swing, but their phase noise can be improved more linearly with increasing bias current, and thus they can achieve lower phase noise with a sufficiently large bias current. Based on the results, a dual-band quadrature voltage- controlled oscillator (Q-VCO) is systematically designed and implemented in a 0.13- m CMOS process for software-defined -radio (SDR) applications, in which the two-port topology is used in the low band for low phase noise and the one-port topology is employed in the high band for low power consumption. The prototype achieves a dual-band operation with in-phase and quadrature-phase (IQ) output signals from 2.7 GHz to 4.3 GHz and from 8.4 GHz to 12.4 GHz. At 3.6 GHz and 10.4 GHz, phase noise at 3 MHz offset of dBc/Hz and dBc/Hz and sideband-rejection ratios (SBR) of 37 dB and 41 dB are measured, respectively.