Why are we adding Butterworth passive filter always at the output of the DACs. Should'nt we use bessel filter for multicarrier systems?
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The goal of the filter is to reject DAC clock leakage and harmonics from passing to the next stage. Although a Bessel filter has the characteristics of very low group delay variation and hence should not degrade the EVM performance of the multiple carriers, the Bessel offers very little stop-band rejection for any practical order filter design. The Butterworth filter offers the flattest magnitude response, and the Butterworth’s group delay variation can have minimum impact of EVM performance as long as the corner frequency is not set to be too close to the edge of the highest carrier frequency.
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