Testing amplifiers for 5G with up to 2 GHz analysis bandwidth: Page 4 of 4

January 09, 2018 //By Martin Schmähling, Rohde & Schwarz
Testing amplifiers for 5G with up to 2 GHz analysis bandwidth
The future 5G cellular standard includes the transmission of signals in the microwave range at 28 GHz or 39 GHz with bandwidths of several hundred MHz. As a result, 5G component developers require a flexible test and measurement solution to analyse signals at these frequencies and bandwidths.

Correcting memory effects

As well as nonlinear effects, memory effects in the amplifier produce a frequency response: essentially a distortion of the amplitude or phase versus frequency. Until recently, correction of these memory effects has been very complex, with elaborate mathematics such as Volterra series required to describe this response. Today, options like the FSW-K18D DPD measurements extension greatly simplify the process. For every arbitrary signal, the software calculates the frequency response along with the EVM value that describes the signal quality. Instead of approximating with polynomials, it applies iterative approximation via the individual samples. The signal played back by the generator and distorted by the device under test is measured and the pre-distortion is adjusted. After multiple iterations, the signal generator outputs a signal with optimal pre-distortion. In this way, the option compensates both nonlinear distortion and frequency response for a predefined signal sequence. The result delivers the best possible reference for pre-distortion algorithms employed by the user.

Image 2: Wideband amplifier measurements with a 400 MHz wide signal from the SMW200A signal generator. The windows on the right display the output amplitude and phase changes relative to the input signal (AM/AM and AM/PM curves). The 2 GHz signal generation and analysis bandwidth allows ACLR (Adjacent Channel Leakage Power Ratio) optimization of the first adjacent und second adjacent channel even for a 400 MHz wide signal.

The 2 GHz analysis bandwidth now available in the FSW43 and FSW50 makes it possible to characterize wideband amplifiers.

The author, Martin Schmähling is the Spectrum Analysis Product Manager at Rohde & Schwarz, Munich

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