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Rohde & Schwarz: Digital Predistortion Option Shortens Test Time and Simplifies Amplifier Evaluation
02/25/2014 Source: Interference Technology

Rohde & Schwarz has announced the new R&S SMW-K541 digital predistortion option for its R&S SMW200A high-end vector signal generator.

Predistortion can extend the operating range of amplifiers, says the company, but determining the right correction factors has always been a time-consuming process. The new R&S SMW-K541 digital predistortion option allows users to import predistortion coefficient tables directly into the R&S SMW200A. The signal generator then uses these delta values to adjust the baseband signal in realtime, greatly reducing 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 realtime 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 new R&S SMW-K541 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.


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