A Background Spread-Spectrum Radio Frequency Nonlinear Parameter Measurement Technique

We report a new correlation-based direct sequence spread-spectrum technique that estimates low-pass-equivalent Volterra coefficients for weakly nonlinearRF systems. The methodology provides robust coefficient estimates at test signal amplitudes well below the operating signal level during normal system operation, demonstrating that the technique can be used for "background" nonlinearity measurement. We demonstrate the methodology by measuring third-order Volterra kernels for a power amplifier chain operated in compression with a 10 MHz bandwidth signal at 1960 MHz.