A 2-V 2.5-GHz-104-dBc/Hz at 100 kHz fully integrated VCO withwide-band low-noise automatic amplitude control loop

摘要

The automatic amplitude control (AAC) loop is an indispensablenelement for the practical realization of VCOs embedded in a completentransceiver. Its noise however can unacceptably degrade thensingle-sideband-to-carrier ratio (SSCR) performance of the oscillator,nthis problem being even exacerbated in low-voltage circuits. This papernaddresses the design issues of a low-voltage low-noise differentialnLC-VCO with AAC, tunable within a 2.3-2.8-GHz frequency range, fullynintegrated in bipolar technology with 2-V power supply. First, thenmechanisms through which the AAC noise affects the output phase arenidentified as the poor indirect stability and the AM-to-PM conversionndue to the varactors. The effect of the AAC noise is discussed andnsubstantially reduced with suitable design choices. We show that thenachievable noise-to-signal ratio is bounded by the shot noise comingnfrom the bias source of the differential oscillator, an intrinsic limitnset by the low supply voltage which does not allow for degeneration ofnthe tail transistor. Second, the design of the AAC is discussed. A largengain-bandwidth product (GBWP), about 100 MHz, has been implemented innorder to correct for the fast oscillation amplitude variations andnreduce the effect of the ground line disturbances. The expected value ofnthe phase noise level, SSCR at 100 kHz =-104 dBc/Hz, is tightly matchednby the experimental results. The core oscillator dissipates 7 mA, whilenless than 600 ΜA are drawn by the AAC circuit