A Colpitts Oscillator Design for a GSM Base Station Synthesizer

This paper presents the design of a VCO using a Colpitts topology. The VCO system is fully integrated and suitable to operate in GSM base station synthesizers. The challenges and requirements for this application will be discussed and the possibility of achieving the performance of the oscillator will be demonstrated. The topology of the VCO core is a varactor tuned Colpitts oscillator which achieves a phase noise of -148 dBc/Hz at 1.8 MHz offset frequency. A 130 nm RF-CMOS process was used for the implementation. The process supports thick oxide devices for higher breakdown voltages. These transistors were chosen in order to obtain the highest possible voltage swing in the VCO core.