NI 5441
Pre-Filter Offset

Pre-filter offset can be used to add offset to the I and Q stream during signal generation. The I and Q pre-filter offsets can be changed independently by setting the Pre-Filter Offset I and Pre-Filter Offset Q properties. The offset can range from negative Full Scale (−1) to positive Full Scale (+1). Any time the pre-filter offset changes, the OSP block ignores all overflows for the next 50 IQ samples. If an overflow occurs during these 50 samples, the data is clipped but an error is not returned. Overflows are common during the first 50 IQ samples after a pre-filter offset change because the abrupt change is seen as a transient by the FIR filter. You can use the pre-filter offset to simulate I/Q DC offset impairments.

Pre-Filter Offset Overflow

Any time the following condition is not true for the I or Q data stream, an overflow occurs when pre-filter 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 pre-filter gain, attenuate the waveform data, or reduce the pre-filter offset.

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