NI 5442
Pre-Filter Offset

Prefilter offset can add offset to the I and Q stream during signal generation. You can change the I and Q prefilter offsets independently by setting the Pre-Filter Offset I and Pre-Filter Offset Q properties or the NIFGEN_ATTR_OSP_PRE_FILTER_OFFSET_I and NIFGEN_ATTR_OSP_PRE_FILTER_OFFSET_Q attributes. The offset can range from negative full scale (−1) to positive full scale (+1). Any time the prefilter offset changes, the OSP block ignores all overflows for the next 71 IQ samples. If an overflow occurs during these 71 samples, the data is clipped but an error is not returned. Overflows are common during the first 71 IQ samples after a prefilter offset change because the abrupt change is seen as a transient by the interpolation filters. You can use the prefilter offset to simulate I/Q DC offset impairments.

Prefilter Offset Overflow

Any time the following condition is not true for the I or Q data stream, an overflow occurs when prefilter offset is applied:

-1 ≤ (User Data × Pre-Filter Gain) + Pre-Filter Offset ≤ 1

If an overflow occurs, the data is clipped and NI-FGEN returns an error. To prevent data clipping, reduce the prefilter gain, attenuate the waveform data, or reduce the prefilter offset.

Tip  To disable error reporting caused by OSP overflows, use the OSP Overflow Error Reporting property or the NIFGEN_ATTR_OSP_OVERFLOW_ERROR_REPORTING attribute.