digital down converter (3G) (DDC)

The Digital Down Converter(DDC) is a digital high frequency circuit that mixes a high frequency digital signal down to baseband. The center frequency of such a signal is 0 Hz. Simultaneously with the downmixing, the Digital Down Converter reduces the data rate and thus the computational effort.

From the mixing technique, the received RF signal is summed with an oscillator frequency and the frequency for the baseband is filtered out by the IF filter. Then the signal transformed into the baseband is digitized by means of an AD converter. All other mixing frequencies are filtered out. The mixing itself is performed with two signals that are 90 ° out of phase. The two resulting signals are the I and Q signals for demodulation.

DDC converters are used in communications technology, mobile communications, RF measurement technology and in Software Defined Radios( SDR) to scale the sampling rate of the signal. They are designed as chips, field programmable gate arrays( FPGA) or ASICs ( application specific integrated circuit).