Transformer-Based Current-Reuse Armstrong and Armstrong–Colpitts VCOs

This brief proposes two new types of current-reuse voltage-controlled oscillators (VCOs). One is a current-reuse Armstrong VCO (CR-AVCO) and the other is a complementary current-reuse Armstrong-Colpitts VCO (CR-ACVCO). Two one-transistor-based NMOS and PMOS AVCOs are combined into a complementary current-reuse form by sharing a transformer. The CR-ACVCO further improves the CR-AVCO by adding the Colpitts capacitive feedback, which has higher negative transconductance and, consequently, lower phase noise than that of the CR-AVCO. All the inductors are realized with one five-port transformer. The phase noise of the CR-AVCO and CR-ACVCO at 1-MHz offset frequency is -113.3 dBc/Hz at 4.84 GHz and -120.1 dBc/Hz at 5.3 GHz, respectively. The CR-AVCO and CR-ACVCO consume 2.32 and 2.74 mW from a 0.8- and 1.2-V supply, resulting in a high figure of merit with tuning range (FoM^T) of -187.5 and -194.2 dBc/Hz, respectively. The proposed CR-VCOs are implemented in a 0.13 μm CMOS.