Improving performance in a VXI or PXI test system using distributed DSP

This paper presents the results of a study into the use of distributed digital signal processing (DSP) at the instrument level in a VXI and PXI based test system and the effects on test time. One of the limiting factors in testing mixed signal or analog devices using standard bus based instruments is the transfer speed from the instrument to the controlling computer of large amounts of waveform data. This is important as these types of tests use non-deterministic, quantized signals that must be mathematically processed to extract test information. This processing can either be done at the instrument or at the central controller. If the processing is done at the instrument then only the results are transferred to the controller. If the controller does the processing then the raw data must be transferred to and from the instrument. Using two instruments, one in VXI and one in PXI, this paper measures the effects of typical tests contrasting the measurements as done in the central processor as opposed to a distributed DSP processor in each instrument. For each acquisition instrument, test were implemented by capturing the data and moving it to the controlling computer where it was processed to extract test results, or by using the instruments on board DSP so only the final test results were sent to the controlling computer. The study results shows that a significant improvement in test time can be made by selecting "smart" instruments for the test system when using PXI or VXI based instruments.