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Abstract-Many problems in radar and communication signal processing involve radio frequency (RF) signals of very high bandwidth. This presents a serious challenge to systems that might attempt to use a high-rate analog-to-digital converter (ADC) to sample these signals, as prescribed by the Shannon/Nyquist sampling theorem. In these situations, however, the information level of the signal is often far lower than the actual bandwidth, which prompts the question of whether more efficient schemes can be developed for measuring such signals. In this paper we propose a system that uses modulation, filtering, and sampling to produce a low-rate set of digital measurements. Our "analog-to-information converter" (AIC) is inspired by the recent theory of Compressive Sensing (CS), which states that a discrete signal having a sparse representation in some dictionary can be recovered from a small number of linear projections of that signal. We generalize the CS theory to continuous-time sparse signals, explain our proposed AIC system in the CS context, and discuss practical issues regarding implementation.

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The objective of this study was to characterize the polarization impedance (resistance and capacitance) of several common metal/0.9% saline interfaces operated at low-current density and to thereby provide a useful reference for those wishing to calculate the impedance of such electrodes. The series-equivalent resistance (R) and capacitive reactance (Xc) of stainless steel, platinum, silver, MP35N, palladium, aluminum, rhodium and copper electrodes, all having a surface areas S = 0.005 cm2 and all in contact with 0.9% saline, were measured as a function of frequency (100 Hz to 20 kHz) at low-current density (0.025 mA/cm2). For all the metals tested, both R and Xc decreased with increasing frequency and the relationships were linear on a log-log plot. That is, R and Xc exhibited power-law behavior (R = A/f alpha and Xc = B/f beta). However, it was not generally true that A = B and alpha = beta = 0.5 as stated in the Warburg low-current density model. Furthermore, the Fricke constant phase model in which alpha = beta and phi = 0.5 pi beta was found not to be applicable in general. In particular, the constraint that alpha = beta was a good approximation for most of the metals tested in this study, but the constraint that phi = 0.5 pi beta did not hold in general. Although the Warburg low-current density model provides a useful conceptual tool, it is not the most accurate representation of the electrode-electrolyte interface. The Fricke constant phase model is a better representation of electrode behavior, but it also may not be valid in general. We have found that a better representation is provided by the general power-law model R = A/f alpha and Xc = B/f beta, where A, B, alpha, and beta depend on the species of both the metal and electrolyte and A and B depend, in addition, on electrode area. Using this model and the data presented in this study, the impedance of an electrode-electrolyte interface operated at low-current density may be calculated as formula see text where S is the surface area of the electrode in cm2.

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In this paper, we present a systematic synthesis methodology for fully integrated wideband low noise amplifiers that simultaneously optimizes impedance matching, noise figure, and other performance parameters. Leveraging an accurate analytical model, we hierarchically couple global optimization techniques with local convex optimization methods to efficiently locate optimal wideband LNA circuits. The results indicate that the methodology yields significant improvement in key LNA design constraints over existing methodologies while achieving up to one order of magnitude speedup in computational performance.