The design of a 5 GHz VCO with phase noise performance analysis using MOSFET-based current sources

This paper describes the design of a 5 GHz cross-coupled LC VCO implemented in the single-supply S35D4M5 0.35 μm BiCMOS process by Austriamicrosystems. The paper further discusses the phase noise performance of various MOSFET-based current source topologies when implemented within the VCO. MOSFET current source characteristics such as flicker noise, device numbers, feedback, and the output resistance were investigated in order to achieve the best phase noise performance. The VCO operates with a tuning range of 4% about the centre frequency of 5 GHz. A phase noise of -108.0 dBc/Hz at a 1 MHz offset from the carrier frequency is achieved. The design also demonstrates a 60% improvement in frequency drift within the commercial temperature range when temperature stability circuitry is introduced.