Application Note: Optimizing LNA Performance for CDMA Application

By California Eastern Laboratories

Abstract
This application note will review the process by which designers can take advantage of the latest simulation tools such as Xpedion's Design Systems to achieve the optimal performance required by new digital communication system encryption including Code Division Multiple Access (CDMA).

Traditionally, for small signal amplifiers, there has been three distinct and generally incompatible basic design approaches that have met most design goals: the high gain, low return loss conjugately matched amplifier, the low noise amplifier and the high output power amplifier.

With the emergence of new technologies, in particular digital communications, the need for composite amplifiers that meet specific design goals not met by standard designs has increased. A previous article demonstrated how the different basic design types could be accomplished using a low cost NEC HJ-FET in a plastic package. This article will emphasize improved performance of the original low noise amplifier for PCS by using series feedback techniques and predicting the system performance on the digital signal through nonlinear simulation analysis.

While the designs proposed may not yield the optimum design solutions for all PCS applications, it does introduce a few important RF and microwave techniques that can be applied to other digital applications....

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