RAPID enhancements in digital signal processors (DSPs) have made it possibl
e for designers to use digital predistortion to perform real-time correctio
n of distortion in RF power amplifiers (PAs). Unfortunately, unlike purely
analog-based solutions, this technique puts stringent requirements on sever
al components in the transmission chain, including predistortion circuits,
data converters, reconstruction filters, and the RF transmitter (Tx) compon
ents (Fig. 1). These constraints arise because there must be a perfect tran
smission path between the predistorter and the nonlinear PA, since any erro
rs in this path will result in increased adjacent-channel power (ACP). Alth
ough an adaptive digital predistortion ssystem can compensate for some of t
he nonlinearities in the forward path not attributable to the PAs, many oth
er imperfections cannot not be overcome. Therefore, a successful implementa
tion of digital predistortion requires an understanding of potential system
-level limitations and the means of overcoming them. This article presents
an empirical overview of circuit errors in non-adaptive systems. Since many
of the components in the correction loop exhibit characteristics similar t
o those in the forward path, the information presented is also applicable t
o a fully adaptive, digital predistortion system.