The objective of the bachelor graduation project detailed in this thesis is the development of a system suited for testing radio frequency (RF) power amplifiers (PAs). This PA test system is in particular set up for testing two-transistor interpolating-supply amplifiers.
Interpolating-supply PAs are efficiency-enhanced by employing multiple transistors supplied by different, fixed drain supply voltages, leading to different efficiency characteristics, which are then combined by switching between the transistors, resulting in an enchanced overal efficiciency. Turning on the right amplifying transistor takes place digitally by pre-adjusting the different data inputs or control of gate biases.
The PA test system is required to provide support for measurement and signal generation for 40 dBm output power of a 20 dB gain PA. Moreover, it is required to provide remote control access to the measurement equipment and automation of the tests, implemented in MATLAB.
The to-be-measured PA performance metrics were constrained to static tests for drain efficiency, power-added efficiency, AM/AM distortion, total harmonic distortion (THD) and intermodulation distortion (IMD).
In order to meet the requirements while making use of the available resources, it was recognized that the following subsystems were necessary:
• Baseband signal generation using a DAC;
• RF signal generation using a to-be-calibrated IQ modulator;
• Pre-amplifier, by own design; and
• Spectrum analyzer, controlled remotely.
The baseband signal generation subsystem was characterized with respect to noise and gain performance, which resulted in the making of noise-reducing LC low-pass filters. The provided IQ modulators were successfully calibrated for device non-idealities in an automated MATLAB GUI, allowing for clean RF signal generation. Three pre-amplifiers with over 27.5 dB power gain were realized for sufficient PA input power. A set of MATLAB functions and scripts for the spectrum analyzer and top-level control was written, enabling semi-automatic PA testing.
At the time of writing this thesis, the PA test system was put in use to characterize and evaluate two interpolating supply PAs. For automation, another GUI was implemented for the PA test system. The system proved to be able to determine PA input, output and DC power to measure the gain, linearity and efficiency in multiple static tests and for different PA bias conditions. Also THD and IMD for single-transistor were measured using the PA test system. The results were to a realistic extent similar to the simulated PA characteristics, aside from some anomalies which could possibly be explained by PA design implementation mistakes or test system nonidealities.