The implementation of a digital sine-wave oscillator using the TMS320C25: distortion reduction and applications

The implementation of a digital sine-wave oscillator using the TMS320C25 digital signal processor (DSP) is described. The system is implemented with the Dalanco Spry model 25 DSP board, and a software system is designed whereby an IBM PC host computer provides control of the waveform generator functions and parameters. Waveforms are generated using the look-up-table (LUT) method. The direct LUT method has the disadvantage of increased harmonic distortion when fractional addressing is implemented to improve frequency resolution. This type of distortion can be reduced by linear interpolation or other methods. The existing methods of direct LUT and linear interpolation are implemented and compared with the present approach. The proposed method uses a trigonometric identity to reduce the harmonic distortion of the sine wave by effectively increasing the table length of the direct LUT method. The authors present the results of an experiment performed in the digital domain, without consideration of the problem of analog reconstruction. Waveforms for the sum of two sine waves, a frequency swept sine wave, amplitude modulation, and frequency modulation are shown as applications of the waveform generator.<
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