A systematic approach to the realization and design of actively compensated two OA voltage amplifiers
Several actively compensated voltage amplifiers (ACVAs) employing two operational amplifiers have been reported separately in the recent literature. In this article, the results of a systematic and comprehensive study of both non-inverting and inverting such ACVAs are presented. Using a combination of practical and theoretical considerations, ACVAs are first divided into classess. Each class is further divided into types. Realizability conditions are then derived for each of the different types. These conditions lead directly to a set of useful realizations. the performance of each realization is considered in detail with respect to several practical considerations of interest, such as magnitude and phase errors, effect of the second pole of the operational amplifiers (OAs), tunability, maximum signal handling capability, etc. the results of practical experiments are also given. Experimental results agree closely with the theoretical predictions.
We investigate the OLS-based estimator s2 of the disturbance variance in the standard linear regression model with cross section data when the disturbances are homoskedastic, but spatially correlated. For the most popular model of spatially autoregressive disturbances, we show that s2 can be severely biased in finite samples, but is asymptotically unbiased and consistent for most types of spatial weighting matrices as sample size increases.