Comparison of a fully integrated differential voltage controlled Colpitts oscillator to the cross-coupled oscillator topology

In that paper a detailed comparison between the differential Colpitts oscillator and the well-known cross-coupled oscillator topology is presented. Frequency tuning is realized by using a combination of switchable capacitors and an analog varactor diode. The main focus is to minimize the phase noise, which is a limiting factor in the realization of RF-radios for modern communication systems. Other criteria are power consumption, tuning range and chip area. The charge-phase transfer function, which characterizes the impulse-sensitivity function (ISF), is calculated. Thus, the impact of harmonics, which are coupled into the oscillator, can be determined. Effects like VDD pushing and load pulling are covered also. All oscillators presented in this paper are manufactured in a 0.35 mum SiGe-BiCMOS process