The new R&S SMW-K541 digital predistortion option from Rohde & Schwarz allows users to import predistortion coefficient tables directly into the R&S SMW200A high-end vector signal generator. The signal generator uses these delta values to adjust the baseband signal in real time. The option greatly reduces test times since predistorted waveforms no longer have to be tediously recalculated and imported into the generator.

Amplifiers are most efficient when they operate near their maximum output power, which occurs in the nonlinear range. Although more power efficient, this results in distortions at the amplifier output, which considerably diminishes the amplifier's RF performance. Developers, especially developers of envelope tracking power amplifiers for smartphones, base stations and tactical radios, use digital predistortion to counteract this problem. In envelope tracking, the supply voltage tracks the envelope of the RF signal. Envelope tracking can optimize efficiency, but is a valid design approach only when predistortion is used to compensate for nonlinear effects.

The R&S SMW-K541 digital predistortion option allows users to import an AM/AM or AM/PM table with correction factors directly into the R&S SMW200A. The R&S SMW200A uses the table values to automatically calculate in real time an amplitude and phase offset for each I/Q sample. The original waveform file remains unchanged. Conventional solutions require users to import a new, predistorted waveform file into the signal generator each time the level changes.

Developers can use the digital predistortion option on all communications standards supported by the R&S SMW200A as well as on their own custom waveforms. For envelope tracking tests with predistortion, the digital predistortion option can be configured and seamlessly combined with the R&S SMW-K540 envelope tracking option so that the envelope signal can be generated either from an undistorted or predistorted signal.

The test solution will be presented at the Mobile World Congress 2014 in Barcelona in Hall 6, Stand C40.