NI 5441
Pre-Filter Gain

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

Pre-Filter Gain Overflow

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

-1 ≤ User Data × Pre-Filter 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 pre-filter gain.

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.