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## DUC vs DDC | Difference between DUC and DDC

This page on DUC vs DDC describes difference between DUC and DDC. DUC stands for Digital Up Conversion and DDC stands for Digital Down Conversion. Both of these modules are used in Software Defined Radio based systems. Refer SDR basics➤➤.

### DUC-Digital Up Conversion

The figure-1 depicts block diagram of DUC (Digital Up Conversion). As shown, the function of DUC is to convert digital baseband samples into digital IF samples.

The device which does digital up conversion is known as Digital Up Converter. D/A converter is used after this module in order to convert digital IF samples into analog IF signal.

RF up converter follows D/A converter which converts IF signal to RF signal for transmission. Hence IF translation frequency is determined by LO (Local Oscillator). Finally RF Power Amplifier is used which amplifies the signal to take care of path loss from transmit end to receive end.

The Digital Up Converter consists of following modules:
• Interpolation filter
• Digital Mixer
• Digital Local Oscillator

Here Mixer generates 1 output sample for two input samples.
➨Sample frequency of mixer output = D/A sample frequency = Fs
➨LO Sample Rate = Baseband Sample Rate = Fs
➨As baseband sample frequency is much lower
compare to LO sample rate of Fs, Interpolation filter is used.

Interpolation filter is used to increase sample frequency of baseband signal by factor of N. This is known as interpolation factor.
Refer Interpolation basics➤➤ and Interpolation MATLAB Code➤➤.

Ratio between needed sample rate at output and baseband sample rate at input is determined using interpolation factor (N).
• Baseband bandwidth = 0.8 * Fb
• Output sample frequency Fs = Fb * N

### DDC-Digital Down Conversion

The figure-2 depicts block diagram of DDC (Digital Down Conversion). As shown, the function of DDC is to convert digital IF samples into digital baseband samples.

The device which does digital down conversion is known as Digital Down Converter.

The Digital Down Converter consists of following modules:
• Digital Mixer
• Digital Local Oscillator
• Low Pass Filter

In decimation process, one sample is kept out of every N digital samples. If the decimated output sample rate is more than twice output bandwidth then no information will get lost. Refer Decimation➤➤ and Decimation MATLAB Code➤➤.

As we are aware that decimated signals will have lower rate and hence can also be stored in less memory. This will greatly reduce cost of the system.

As a whole DDC performs following signal processing tasks:
➨Frequency translation with the help of variable LO device.
➨Low Pass filtering with bandwidth controlled by decimation process.

The baseband signal bandwidth in DDC is set using decimation factor(N) and the lowpass FIR filter:
• Baseband sample frequency Fb = Fs / N
• Baseband bandwidth = 0.8 * Fb