True differential measurements up to 40 GHz with the R&S ZVA and R&S ZVT
January 17, 2011
Up to now, measurements on balanced components had to be performed in a roundabout way: Network analyzers were only able to mathematically calculate the differential parameters from unbalanced single measurements. Rohde & Schwarz has now introduced a software option that adds a true differential measurement mode up to 40 GHz to the R&S ZVA and R&S ZVT network analyzers. It is thus possible for the first time to precisely characterize nonlinear balanced components, which are increasingly included in mobile phones. More and more RF components that are operated with balanced signals are being built into wireless communications equipment. Such components can be characterized using a network analyzer. To determine the compression characteristics of a balanced amplifier under real-world operating conditions, for example, the amplifier must receive true differential- and common-mode stimulus signals. Up to now, the characteristics were calculated by overlaying several unbalanced stimulus states. This approach is not equivalent to use under real conditions and can lead to deviating measurement results, in particular with DUTs in nonlinear operation. Rohde & Schwarz now presents an enhancement for the network analyzers of the R&S ZVA and R&S ZVT family which allows fully corrected measurements using true differential signals up to 40 GHz. In this true differential measurement, two internal generators generate signals of identical amplitude and 0° and 180° phase offset (phase deviation <1°). The network analyzer resets the amplitude and phase relation at each test point and thus also takes into account fluctuations of the DUT's input reflection. The measured differential wave quantities and thus also the mixed-mode S parameters are fully corrected of system errors. The new option can be integrated into the instruments by means of a software update and requires no additional hardware for calibration or measurement. It is easy to switch quickly between the virtual differential approach currently used and the new true differential mode. For direct comparison of the measurement results, the two methods can be applied simultaneously. In addition, it is possible to provide the DUT with a differential-mode or a common-mode stimulus and to measure the absolute output power in differential or common mode. The amplitude or phase relation of the differential signal is variably adjustable. It can also be swept, making it possible to simulate nonideal real stimulus states. The R&S ZVA -K6 true differential measurements option for the R&S ZVA and R&S ZVT is now available from Rohde & Schwarz.