Memory Reduced and Fast DDS Using FPGA

Dr. R. K. Sharma, Gargi Upadhyaya
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Direct digital synthesis is a method of creating arbitrary waveforms of desired frequency. A general DDS system comprises analog and digital part. Phase accumulator and LUT make digital part and DAC makes analog part. This paper presents 12 bit memory reduced FPGA based architecture of DDS. Phase truncation and quadrature symmetry of sine wave are used to achieve higher ROM compression. Dither is also used to achieve error free output. This design has been implemented on SPARTAN-3E FPGA with maximum clock frequency of 50 MHz. We have used LTC2624 quad DAC with 12 bit resolution which introduces very less amount of harmonics hence LPF is not needed. This design uses only 128 memory locations. Hence it is suitable for applications where system speed, memory and size of the system are main concern. Its wide and flexible range of frequency make it useful in RF transmission, Biomedical function generators and Modulation.