Original Date: 01/23/1995
Revision Date: 01/18/2007
Information : Evaluation of High Resolution Digitizers
At Sandia National Laboratories (SNL), a suite of tests has been developed to characterize high resolution digitizers by using coherence analysis. Previous analog-to- digital conversion was performed upon command from a computer program which associated a data sample with the time it was acquired. With new high resolution analog-to-digital conversion, timing is more critical. Special facilities and procedures for evaluating the performance of high resolution digitizers have been developed.
The primary use of these digitizers is to process the signals produced in earth motion when an underground nuclear test is performed (typically in violation of treaty). It is vitally important that these digitizers are capable of identifying a small signal, even if it occurs within a large signal (such as an earthquake). The usual method of characterizing a device such as this is to compare its output response to a known input signal. However in this case, signal generators capable of producing a signal pure enough to challenge the specifications of the highest resolution digitizers have only recently become available and are very expensive. In addition, they provide only tonal signals. Recognizing this, SNL analyzed the parameters which are most important to characterize the digitizer and have determined that these parameters are primarily internal noise characteristics, linearity, dynamic range, and timing precision and accuracy. From this information, they developed tests to characterize the digitizers.
These tests include several data analysis procedures consisting of coherence analysis, Noise Power Ratio testing, Total Harmonic Distortion testing, and other straightforward tests such as AC and DC accuracy. Almost all these tests can be run "at temperature" to check for operation under actual deployment conditions or specifications. These tests provide a realistic estimation of expected performance of the high resolution digitizer in an environment where detection of small signals in the presence of large signals is important.
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