An Ultra‐Wideband Low Noise Colpitts VCO Using SiGe Bi‐CMOS Technology

An ultra‐wideband voltage‐controlled oscillator (VCO) based on the Colpitts structure is proposed in this work. The entire circuit consists of four Colpitts VCO cores operating at different frequencies. Every VCO core employs two single‐ended Colpitts oscillators arranged back‐to‐back and sharing a common LC resonating tank. The coupling coefficient between the two single‐ended Colpitts oscillators is increased by introducing a transformer placed on the emitter node of the core transistor, which ensures two Colpitts oscillators oscillating in differential mode. Furthermore, a series of analogue signal processing circuits, including a fundamental signal amplifier, second harmonic signal amplifier, and frequency doubler, are employed to amplify the second and fourth harmonic signals, thereby greatly expanding the operating frequency bandwidth of the proposed VCO. The oscillating frequency of the proposed Colpitts VCO ranges from 3.5 to 7 GHz, and the maximum frequency can reach up to 14 GHz or 28 GHz through generating the second or fourth harmonics. The measured phase noise performance at 1 MHz offset is lower than ‐130dBc/Hz, −124 dBc/Hz and −118 dBc/Hz at 3.5 GHz∼7 GHz, 7GHz∼14 GHz, 14 GHz∼28 GHz frequency bands, respectively. The power dissipation of the entire VCO is typically around 60 mW under a 3.3 V power supply.