Simple nonlinearity evaluation and modeling of low-noise amplifiers with application to radio astronomy receivers

This paper describes a comparative nonlinear analysis of low-noise amplifiers (LNAs) under different stimuli for use in astronomical applications. Wide-band Gaussian-noise input signals, together with the high values of gain required, make that figures of merit, such as the 1 dB compression (1 dBc) point of amplifiers, become crucial in the design process of radiometric receivers in order to guarantee the linearity in their nominal operation. The typical method to obtain the 1 dBc point is by using single-tone excitation signals to get the nonlinear amplitude to amplitude (AM-AM) characteristic but, as will be shown in the paper, in radiometers, the nature of the wide-band Gaussian-noise excitation signals makes the amplifiers present higher nonlinearity than when using single tone excitation signals. Therefore, in order to analyze the suitability of the LNA's nominal operation, the 1 dBc point has to be obtained, but using realistic excitation signals. In this work, an analytical study of compression effects in amplifiers due to excitation signals composed of several tones is reported. Moreover, LNA nonlinear characteristics, as AM-AM, total distortion, and power to distortion ratio, have been obtained by simulation and measurement with wide-band Gaussian-noise excitation signals. This kind of signal can be considered as a limit case of a multitone signal, when the number of tones is very high. The work is illustrated by means of the extraction of realistic nonlinear characteristics, through simulation and measurement, of a 31 GHz back-end module LNA used in the radiometer of the QUIJOTE (Q U I JOint TEnerife) CMB experiment.

[Hepatitis B and hepatitis delta in young inmates]

The prevalence of infection by hepatitis B (HBV) and delta (HDV) viruses and presumably related variables were evaluated in a prison for young male convicts, aged 16-21 years (n = 686), 55.1% of convicts were positive for one or more VHB markers, and 7.1% were positive for HBsAg; 89.7% of these were negative for IgM anti-HBc (chronic carriers), while 36.6% were positive for HBeAg. Anti-delta antibodies were detected in 37.5% of chronic carriers. The seropositivity of HVB markers was much higher in parenteral drug abusers (PDA) as compared with non PDA (76.3% vs 26.7%, p less than 0.0000001, OR = 8.82). Among PDA, it was higher in regular users than in occasional ones (83.3% vs 62.9%, p = 0.0001, OR = 2.95) and in those who had acquired the habit at an early age (p = 0.035). The stratified analysis also showed an association of VHB infection with other variables, basically ethical and prison-related. The possibility to develop active immunization programs is evaluated.