AN9718: Analog Amplifier Linearity Characterization via Probability Weighted Multitone Power Ratio Testing (HI5905, HC6094)

This application note discusses methodology for testing analog amplifiers designed to process DMT (discrete multitone) waveforms, also known as OFDM (orthogonal frequency division multiplexing) waveforms. There is a brief introduction of the DMT waveform where it’s pointed out that a troublesome characteristic of the DMT waveform is a probabilistically large peak to average amplitude ratio. The application note then goes on to derive the probability density distribution for the DMT peak to average ratio (PAR) in preparation for presenting a test methodology. It then discusses the concept of the MTPR (multitone power ratio) test, which consists of a plethora of frequency domain impulses, uniformly spaced over the bandwidth of interest, with the characteristic that periodically a frequency impulse is “missing”, giving the appearance of a “spectral notch”. The object of the test is to pass this MTPR test waveform through the amplifier under test and observe the depth of the “notches” at the output of the amplifier, which will be “filledin” due to any amplifier nonlinearities. Further discussions go on to state that such testing should be done with several MTPR test vectors, each with a unique peak to average ratio, and the composite MTPR of the amplifier is the probability weighted sum of the individual MTPR responses.