Wideband BiCMOS VCO for GSM/UMTS direct conversion receivers

Abstract

With the increasing number of mobile communication standards, a large research effort is put into the task of complete integration of RF voltage-controlled oscillators (VCOs) for multi-band and multi-mode direct conversion transceivers. However, RF VCOs are, at present, not fully integrated in transceivers, since they suffer from poor phase noise and fabrication tolerances. Satisfying the phase noise requirements of GSM, IS-136, or UMTS is a major challenge for fully-integrated VCOs. Traditionally, (integrated) RF VCOs are realized with bipolar devices due to their low high-frequency noise and low flicker noise corner frequency. Recently, several publications on CMOS VCOs have appeared, reporting excellent phase noise performance at large frequency offsets. These VCOs, however, suffer from degraded close-to-carrier phase noise due to the high flicker noise of the CMOS devices, and from a low-resistive substrate allowing only low-Q spiral inductors and resulting in higher power consumption. Furthermore, many of the VCOs have nonlinear tuning characteristics because of the abrupt C-V curve of the MOS diode. This wideband BiCMOS VCO for multimode direct conversion transceivers achieves low phase noise both close to the carrier and at large frequency offsets. In addition the VCO must have a wide but sufficiently linear tuning characteristic and low pushing sensitivity. The design must provide sufficient performance margin for production tolerances.