Filter Delay

The delta-sigma ADCs and DACs on DSA devices and the NI 9225, NI 9229, NI 9233, NI 9234, NI 9235, NI 9236, NI 9237, and NI 9239 employ digital filtering that imparts a delay of several sample intervals. The filter delays are equal in a homogeneous system, so these delays cancel out when performing phase measurements between channels. However, the filter delays differ in a heterogeneous system. This can introduce errors in phase comparisons between channels on different devices or between channels on similar devices running at different rates. Such phase errors are always deterministic, and you can account for them in software. Refer to your device documentation for more information on the digital filters and the delays associated with them.