Nonlinear amplifier noise product ratio modeling and simulation

A noise product ratio (NPR) test and/or simulation is a traditional way of examining the nonlinearity of devices such as high-power amplifiers (HPAs). The advantage of NPR testing and/or simulation includes the ability to use a noise source and filters to obtain the band of noise with the appropriate notch for test purposes, which is typically more easily accomplished than performing BER testing and/or simulation for the specific modulated carriers that are anticipated to go through the HPA. Additionally, the types of signals anticipated to go through the HPA may be quite variable, and not all possibilities can be practically tested and/or simulated using conventional methods. NPR testing helps preclude the need for testing every possible signal combination. In this paper the authors discuss a simulation and modeling technique for determining NPR for a nonlinear amplifier with arbitrary AM/AM and AM/PM transfer curves. While NPR tests are typically done at radio frequency (RF), the model chosen is a baseband model. Specific examples of the transfer curves are chosen to demonstrate the utility and versatility of the simulation and modeling technique. Importantly, the approach described in this paper has been validated by detailed RF lab measurements.