Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 9, NO. 4, JULY/AUGUST 1997

The linearity requirements of power amplifiers for use in digital cellular systems can be specified by several figures of merit, including intermodulation distortion and adjacent channel power ratio. Experimentally, while each is a figure of merit that describes some aspect of amplifier linearity, there appears to be no simple a priori relationship between two-tone intermodulation distortion and adjacent/alternate channel power ration. The absence of a simple relationship can have significant implications in the design and testing of power amplifiers targeting digital cellular systems.

Introduction

This article is an expanded version of a paper presented at the 1996 Wireless Communications Conference [1]. Many of the newer digital cellular systems have chosen methods of modulating digital information onto an RF carrier where the resulting signal is nonconstant amplitude, thereby requiring a linear power amplifier in the transmitter. This is particularly the case in North American Digital Cellular (NADC), Pacific Digital Cellular and the IS-95 Code Division Multiple Access (DCMA) system. Each system uniquely specifies linearity requirements on the transmitter power amplifier [2, 3, 4]. Overall, system specifications, including allocated channel bandwidth, channel spacing, base band filtering and bit error rate, when combined with the selected modulation format ultimately dictate power amplifier linearity requirements. Nonetheless, specifications flowed down to the amplifier are in some figure of merit that may take the form of intermodulation distortion (IMD), adjacent channel power ratio (ACPR) and error vector magnitude (EVM), to...