Noise figure control in LNA - Low-frequency noise reduction in Operational Amplifiers

i - Noise figure control in LNA Noise figure reduction in LNA for portable terminals and cellular phones have been investigated in cooperation with the RF group. In demanding applications, such as re-configurable, multistandard, multi-frequency, the portable terminal should optimize its performances by adapting the power consuption and noise figure to the different operating conditions in a time-varying environment. Aiming at longer battery life, maximum signal-to-noise ratio operation is not always the best choice. In presence of strong signal and weak blockers, signal-to-noise ratio can be lowered without sacrifying the received information quality, with the advantage of a lower power consumption and longer battery life. The common gate LNA has been deeply investigated, giving a unified description of all feedback configurations, providing analytical expressions for gain, noise and linearity for bipolar and CMOS technology. The flexibility of these structures has suggested a novel design methodology oriented to configurable low noise amplifiers both in frequency and in performance. ii - Low-frequency noise reduction in Operational Amplifiers The limits of the conventional chopper stabilization technique for cancelling the 1/f noise has been studied theoretically and with simulations, in cooperation with the Microsystems group. The expected replicas of the 1/f noise at the chopping frequency and its multiples are attenuated by a modified chopping control, based on the use of a square wave clock with a large amount of phase jitter, i.e. with a large linewidth. Simulation done using records of real 1/f noise outputs has shown that the spectrum of the signal is not modified, while 1/f noise replicas are reduced by more than 40 dB. The required circuit for the generation of the chopping signal has been described too; the resulting overhead with respect to conventional techniques is negligible and fully acceptable.