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Dynamic Range Enhancement of High-Speed Data Acquisition Systems

Reversible non-linear amplitude compression is used.

John H. Glenn Research Center, Cleveland, Ohio

The innovation is a technique to overcome hardware limitations of common high-speed data acquisition systems in order to be able to measure electronic signals with high dynamic range, wide bandwidth, and high frequency.

Electronic waveforms exist that exceed the capabilities of state-of-the-art data acquisition hardware that is commonly available. That hardware is still not sufficient to capture these waveforms with enough accuracy and certainty for coherent results. The electronic waveforms that need to be measured simultaneously contain wide bandwidth, high frequency content, a DC reference, high dynamic range, and a high crest factor. To record these waveforms, the current data acquisition hardware needs to increase simultaneously its internal analog bandwidth, quantization bits, sample rate, and analog signal-to-noise ratio. Attempts at recording these waveforms were previously limited to inferior statistical techniques that were not able to provide instantaneous waveform recordings that were unique from the statistical, time-averaged collection.

The innovation is implemented with a custom electronic circuit applied between the input of a data acquisition device, such as an oscilloscope, and a test article to be measured. The innovation also includes a software-based algorithm that is applied to the data acquired through the applied circuit and the data acquisition system. The circuit creates a voltage compression effect with a custom transfer function that is adapted to the voltage range, frequency bandwidth, and electrical impedance of both the test article and data acquisition device. The compression transfer function is later reversed (or decompressed) with a software algorithm to restore the original signal’s voltage from the acquired data. The data is thus improved via better signal-to-noise ratio, better low-amplitude accuracy, better resolution, and preservation of high-frequency spectral content. The circuit can be realized with either passive components or both active and passive components. Either realization is specialized for the test article and data acquisition hardware. The passive circuit in development is specialized for low impedance and extremely high frequencies.

The passive version of the circuit is inexpensive, small, simple, and constructed of common off-the-shelf components. It could be incorporated into a mass-produced probe for data acquisition devices such as an oscilloscope. Currently, the ultra-high-frequency response is being researched and optimized for a final design. The inverse transfer function would need to be applied numerically in post-processing in either the oscilloscope processor or offline on a personal computer with appropriate capabilities. The best application of the concept is for measuring sudden electric discharges.

This work was done by Matthew Laun of Sierra Lobo, Inc. for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-18957-1.

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