NI 5442
Prefilter Gain

Prefilter gain can change the gain of the I and Q stream during signal generation. You can change the I and Q prefilter gains independently by setting the Pre-Filter Gain I and Pre-Filter Gain Q properties or the NIFGEN_ATTR_OSP_PRE_FILTER_GAIN_I and NIFGEN_ATTR_OSP_PRE_FILTER_GAIN_Q attributes. The gain can range from -2.0 to +2.0 (unitless). Any time the prefilter gain 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 gain change because the abrupt change is seen as a transient by the interpolation filters. The prefilter gain can be used to attenuate the IQ data to eliminate overflows in later stages of the OSP block. You can also use the prefilter gain to simulate IQ gain imbalance impairments.

Prefilter Gain Overflow

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

-1 ≤ User Data × Prefilter Gain ≤ 1

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

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.