Characterizing a high-frequency amplifier can be rather tricky. In fact, just configuring a network analyzer for the right set of measurements can be challenging. To ease this process, Rohde & Schwarz (Hants, United Kingdom) offers a 17page-long application note titled, "Performing Amplifier Measurements with the Vector Network Analyzer ZVB." The note, which is based on the firm's model ZVB instrument, begins by illustrating the basic analyzer configuration for amplifier measurement. It then moves on to discuss S-parameter measurements. To perform a two-port calibration, the engineer can use an appropriate manual calibration kit or the company's ZV-Z5x automatic calibration unit. The analyzer can format the complex data from the S-parameter measurement in a number of ways to display the desired result.
The section on input reflection parameters emphasizes that the ZVB can display the statistical analysis of a desired trace. The user can even define an evaluation range for which the analysis is to be performed. In effect, he or she will be giving the characteristics over a defined bandwidth.
The forward transmission coefficient also can be measured. Simply reference the transmitted power on the measured-power receiver of Port 2 to the reference-power receiver of Port 1. The ratio of these parameters provides the forward transmission coefficient, which can be converted into the transmission gain. If the analyzer performs a reverse sweep measurement, the stimulus can be applied from Port 2. The reverse transmission coefficient or isolation characteristics can then be found.
The note offers a lengthy discussion of compression point, which is a measure of a device's linearity. When performing such absolute power measurements, it is important to have the correct power level feeding into the DUT. A power calibration is therefore recommended and the steps to perform it are included.
The application note concludes with a discussion on power-added efficiency. Direct-current (DC) voltages can be measured from two DC measurement inputs, which allow a DC voltage to be sampled and displayed in real time. Alternatively, the result of DC quantities can be derived from the user-defined equation editor. The application note reveals a multitude of such capabilities and display features. Overall, this step-by-step guide succeeds in showing how one VNA performs amplifier measurements.
Rohde & Schwarz UK Ltd., Ancells Business Park, Fleet, Hants, UM GU51 2UZ, United Kingdom; +44 1252 818888, FAX: +44 1252 811447, Internet: www.rohde-schwarz.com/UM