Keysight EXG and MXG X-Series Signal Generators User’s Guide 219Basic Digital Operation for N5172B/82B with Options 653/655/656/657Using Finite Impulse Response (FIR) Filters in the Dual ARB Real-Time Modulation FilterUsing Finite Impulse Response (FIR) Filters in the Dual ARBReal-Time Modulation FilterFinite Impulse Response filters can be used to compress single carrier I/Q waveforms down to justthe I/Q constellation points and then define the transitions similar to the modulation filter in ArbCustom (refer to “Using Finite Impulse Response (FIR) Filters with Custom Modulation” onpage 292). The key difference for dual ARB real-time modulation is that a filter is applied as thewaveform plays, rather than in the waveform data itself.Finite Impulse Response filters can be created and used with both dual arbitrary waveformgenerated waveforms and real-time baseband generated waveforms. For this example, the filter isdefined within the CDMA2000 digital communications format, a dual arbitrary waveform generatedstate.Figure 8-17 Filter MenuMode > Dual ARB > Arb Setup > More > Real-Time Modulation Filter >This softkey changes, dependingon the selected filter–type.Available only when theAvailable only when the filterselected = Gaussianpage 225page 220For details on each key, use key help as described on page 56.Opens the IS–95filter selectionmenu.Enables or disables the Modulation Filter. This filter is typically applied to an Arb Waveformcontaining just the I/Q symbol decision points. The Modulation Filter then effectivelydefines the transitions between the symbol decision points. This means that the filter musthave an oversample ratio of 2 or more. When this feature is active, the Sample Clock Rateis actually the Symbol Rate. Also, the filter must be real (refer to page 232).page 217
