The design of very-wide-band CMOS voltage-controlled oscillators (VCOs) compliant with the phase-noise specifications of cellular transmitters is non-trivial, especially considering the GSM standard, where the phase noise exhibited by the local oscillator (LO, generated by the cascade of VCO, buffers, and usually frequency dividers) should be several dB below -162dBc/Hz at 20MHz frequency offset from the carrier. As shown in , challenging phase-noise requirements can embrace the WCDMA transmitter as well (e.g. -166dBc/Hz at 45MHz frequency offset for WCDMA band VIII), if cheap antenna duplexers are chosen to minimize costs. In such scenarios, and particularly in the very relevant case of WCDMA transmitting at moderate power levels, the LO power efficiency is still one of the limiting factors for a long-lasting battery life, motivating the ongoing quest for VCO power optimization. © 2012 IEEE.
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