A Source Coupled Differential CMOS Complementary Colpitts Oscillator With On-Chip Transformer Tank

A source coupled differential CMOS complementary Colpitts (C-Colpitts) oscillator with an on-chip transformer tank is proposed. Additionally, the on-chip transformer is analyzed through electromagnetic simulation, and the equivalent circuit is modeled with lumped components. The Q factor of an on-chip transformer is compared with symmetrical inductors, which have almost the same inductance. The proposed source coupled differential C-Colpitts oscillator is fabricated with 0.18-mum CMOS technology. With 1.4-V supply voltage, the oscillator shows phase noise of -145.6 dBc at 3-MHz offset in 1.8-GHz oscillation frequency.