A comparative analysis of the CC and CE type buffers in differential LC VCOs for phase noise

In this paper, the fully integrated differential LC voltage controller oscillator (VCO) is designed and fabricated in InGaP/GaAs HBT technology. The VCOs have the different two output buffer structures for low phase noise. To optimize buffers, two oscillators are compared. One is a common-collector buffer VCO (C-VCO), and the other one is a common-emitter buffer VCO (E-VCO). The C-VCO has better phase noise performance than the E-VCO according to the simulation results. In addition, the measurement result of the fabricated C-VCO is as follows. The tuning range is from 1.44 GHz to 1.709 GHz and -13.46 dBm of the output power at 1.708 GHz with balun and cable losses. Furthermore, the phase noise is -110.5 dBc/Hz at 100 kHz and -127.64 dBc/Hz at 1 MHz offset frequencies, respectively. It is fabricated with a die size of 0.85 × 0.9 mm².