NPR (Noise Power Ratio): What is it, How Can I Simulate it and How do I Measure it?

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  • Author: Richard Cavanagh, David Collins, Robert Smith and Liam Devlin

Noise Power Ratio (NPR) is a figure of merit for the linearity performance of RF and microwave amplifiers. It can be a useful metric for multi-carrier systems and provides an indication of the in-band distortion caused by multiple carriers on other channels. NPR has been used for many years and can be measured using noise generators, filters, and a spectrum analyser. More recently the availability of vector signal generators has allowed a higher degree of flexibility for NPR measurement set-ups. There are many approaches to predicting NPR but simulation at the circuit level requires the availability of accurate large-signal transistor models. Two techniques can then be considered, one using a simulated broadband noise source as the input and the other using many individual carriers.

This paper provides an overview of NPR and describes how it can be simulated using Keysight’s ADS. Options for measuring NPR are described and practical NPR measurements of several PRFI-designed mmWave MMIC amplifiers are presented. The measurement set-up makes use of a Rohde & Schwarz (R&S) SMW200A vector signal generator to produce the input signal and an FSW spectrum analyser to measure the output signal and determine the NPR.

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