21.5 A 3.24-to-8.45GHz low-phase-noise mode-switching oscillator

VCO design for cellular applications to achieve universal coverage for a wide range of frequencies (400MHz to 3700MHz) in different standards and meeting stringent out-of-band and in-band phase-noise (PN) requirements is a challenging task. The simplest method to generate I and Q signals in the LO is to use a frequency divide-by-2 which requires the VCO frequency to be an even multiple of f_LO. This method is area efficient and superior for coexistence as it does not generate jammers in other bands. The technique in this work expands the VCO frequency range to ensure 2xf_LO for all cellular bands, notably 3700MHz, with sufficient margin, and meets the most stringent PN specification for a SAW-less GSM transceiver.