Introduction

The recent introduction of high-performance modulation schemes (e.g. (W)-CDMA and OFDM) provides the capability of realizing high-data rate communication links (i.e. up to 100 Mbps from 20 MHz spectrum)[1]. The broadband nature of those signals together with the large difference between the peak and the average power across the modulation bandwidth requires a large number of spectral components to accurately represent the signal statistics. The modulated signal should be amplified by the transmitting chain without loss of information (i.e. low EVM) and with little out-of-band-distortion to avoid interference with adjacent transmitting channels. The quality of the communication link can be translated into specification parameters of the active element of the transmission chain, in the case of the PA, through the device IM3 and ACPR level. In general, it is very difficult to link the technology parameters of an active device directly to its linearity performance, since the linearity achieved for a given PA is the result of its interaction with the surrounding circuitry. For this reason, most attempts to improve the linearity of PAs are currently made at the circuit level.

In order to properly compare different technologies (e.g. SiGe and III-V) or device technology generations, one must provide the optimum loading conditions, at fundamental, harmonic, and baseband frequencies, to the active device during the evaluation phase, ideally under the same driving signal of the final application. This measurement task is intrinsically complex since the broadband nature of the signal of interest conflicts with the narrow-band nature of the currently employed high dynamic range receivers (i.e. narrow IF bandwidth super-heterodyne receivers.