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

Abstract

In that paper a detailed comparison between the differential Colpitts oscillator and the well-known crosscoupled 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 µm SiGe-BiCMOS process.

Differential Colpitts VCO for Enhancing Transceiver Performance in Specified UHF Mobile RFID Environment Conditions

“…A differential Colpitts VCO reports improved phase-noise performance compared to the cross-coupled VCO [22]. Due to the differential nature, the ability of the feedback capacitor to provide negative conductance is relatively small compared to a single-end Colpitts VCO.…”

Direct-conversion RF transceiver and modem IC for UHF RFID reader system

“…B. VCO Since a PA is integrated in this transceiver, common mode rejection is one of most important specifications for RF front end circuitry. A differential Colpitts VCO ( Figure 5) is implemented because it is not as sensitive as the popular differential cross-coupled VCO [2]. The VCO is implemented using all PMOS because PMOS has less flicker noise characteristics than NMOS.…”