A linear variable-gain pulse amplifier for stabilizing systems

Abstract

A linear variable-gain amplifier is described and the main design problems are analysed. Two important variations from more conventional configurations are introduced. The one concerns the position of the variable element, which, it is shown, must be outside the feedback loop if a constant rise time is to be achieved. The other is the use of local feedback for the FET (used as a variable resistance) in order to achieve high linearity. A discussion is given of the inherent linearity of planar and cylindrical FET's, as well as of the same FET's with local feedback. Practical results and a complete schematic are given.