Time-frequency characterization of long-term memory in nonlinear power amplifiers

This paper presents a new time-frequency characterization method for extracting the linear and third-order nonlinear parameters of a PA including long term memory. A dynamic frequency two-tone test signal is developed where the frequency separation between tones increases over time to enable third-order measurements over frequency from a single measurement. A measurement technique is presented using a single Vector Signal Analyzer (VSA) measurement to coherently capture both the test signal and the DUT output sequentially by switching between the two paths during the measurement. The linear and third-order characteristics of a nonlinear PA are estimated from measuring a sequence of dynamic two-tone signals which vary the relative phase of the input tones. Measurement results for the linear response are in good agreement with vector network analyzer (VNA) measurements. Third-order amplitude and phase characteristics are presented over a tone spacing of 1 kHz to 1 MHz centered at 2 GHz for three different power levels.