RF microelectronics
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The design of quadrature local oscillators for CMOS wireless transceivers is still one of the most challenging issues. This paper focuses the advantages of injection locking techniques to achieve high-performance quadrature generators. A synchronizing oscillator sets spectral purity while locked oscillators set quadrature accuracy and drive the mixer LO input capacitances. Two different architectures, realized in a 0.18@mm CMOS technology, are illustrated and compared. The first, using LC tank locked oscillators as frequency dividers, is tailored to UMTS and show high driving capability with low power. Simple and accurate equations for the design are reported. The second quadrature generator, employing coupled VCOs driven by an auxiliary VCO, is tailored to DCS1800 and achieves outstanding phase accuracy and phase noise. Experimental results compare favorably against previously published solutions.