Designing a Power Amplifier Optimized for Predistortion and Scintera’s RF PA Linearizer (RFPAL)

Abstract: Designing a robust RF PA system dependent upon predistortion begins with the design of a RF power amplifier optimized for use with predistortion. There are a number of ways to design RF power amplifiers to achieve various performance goals, but in order for the amplifier system to achieve the best linearity and efficiency when operated with predistortion, the amplifier must be designed to follow the guidelines provided below. These guidelines assume the use of Scintera’s RF PA Linearizer (RFPAL) but are also useful in designing a system based on other types of predistortion. Using a RFPAL like the SC1894, an optimally tuned PA can achieve 20dBc or more improvement in linearity (see Table 1) thus allowing the amplifier to operate at Psat – PAR and at the peak possible efficiency. Conversely, a PA which has not been optimized for operation with RFPAL may achieve little to no improvement in linearity and it will likely fail to meet the spectral requirement.A typical closed loop system requires a feedback path that taps into the PA output, down-converts and then digitizes the signal which may then be used by the linearizer. Therefore a typical feedback path consists of blocks including a down mixer, variable gain amplifier and ADC. As a discrete implementation, these components add additional cost and power consumption to the system. The Scintera RFPAL integrates the linearizer and all necessary feedback components into a single IC. This vastly simplifies (and speeds up) the system implementation and minimizes the additional board space.