A Swept-Sine Pulse Compression Procedure for an Effective Measurement of Intermodulation Distortion

The ability to produce accurate models of nonlinear systems has grown enormously, thanks to the increase in the available computing power, thus making possible to use such models in a wide range of applications. Adopting these techniques not only enables to design much more efficient systems but also increases the need for accurate and straightforward methods to monitor distortion levels, even out of the testing laboratories. In this context, efficient estimators of total harmonic distortion (HD), HD of order $n$ , and intermodulation distortion (IMD) are needed, which are among the most widely adopted indicators of nonlinearity. In this paper, we focus on the IMD, which is a robust feature indicator within the whole systems operating bandwidth, whose measurement is based on the effects produced by the nonlinear system when a composite signal feeds its input. We propose an efficient procedure to measure the IMD allowing the simultaneous evaluation of HD of order $n$ and of total HD. The proposed technique relies and extends the synchronized exponential swept-sine technique for the characterization of nonlinear systems by introducing a suitable double exponential chirp input signal. The method estimates all the distortion-level indicators by processing the response to a single, short-duration signal, showing a moderate computational cost and low sensitivity to ambient noise. These advantages make the application of the proposed method extremely rapid and convenient, even in the measurement of operating field devices. Tests have been carried out both in simulated and real-world scenarios, confirming the proposed approach validity.