The Digital Up Converter (DUC) is the counterpart to the Digital Down Converter
(DDC). It converts a digital baseband signal into a higher frequency intermediate frequency signal. The frequency conversion is performed in a mixer
inaddition to the adjustment of
thesampling rate. The design of the Digital Up Converter and Digital Down Converter depends mainly on the required sampling rate. For example, FIR filters
are used at low conversion rates of about ten, while CIC filters, Cascaded Integrator Combs, are used at higher conversion rates. DUC converters have two inputs for the input signals shifted by 90 ° (I/Q). Both signals pass through separate FIR filters and are then mixed with an oscillator signal from a Numerically Controlled Oscillator (NCO). The sum signal is formed from these two signals, which has a higher sampling rate and a frequency in the intermediate frequency range.