Implementation Numerical Controlled Oscillator(NCO) for Digital Down Converter (DDC)

Abstract

In this modern era, most of the signal processing tasks in wireless communications systems are performed digitally. The use of digital signal processing are greatly increasing in digital modulator and demodulator applications. A Digital Down Converter (DDC) converts a digitized real signal centered at an intermediate frequency (IF) to a baseband complex signal centered at zero frequency. The DDC will select the frequency band of interest and shift it down in frequency, which allows the data rate required to retain all the information to be much lower, and consequently reduces the complexity of any further processing. In addition to down converting, the DDC reduces the sampling rate to enable subsequent signal processing at lower speeds. In DDC, there are three parts namely Numerical Controlled Oscillator (NCO), frequency mixer and the Finite Impulse Response (FIR) Filter. In this final year project, NCO is implemented on a DSP Processor (Texas Instruments) using Code Composer Studio (CCS) software. The code has been downloaded and tested on a TMS320VC5416 DSK Board for a 1 MHz carrier modulated with 1 kHz signal.