Design and Implementation of a Re-configurable Versatile Direct Digital Synthesis based Pulse Generator

Abstract

Direct digital synthesis (DDS) technology has replaced many traditional analogue circuit functions. The frequency, amplitude and phase of a waveform generated using DDS can be precisely controlled. It is possible to achieve remarkably high frequency resolution, fast frequency switching, and modulation can be easily introduced in a DDS generator. However, pulse waveform generated using DDS requires re-loading of the pulse waveform in the waveform memory to vary the pulse parameters which causes phase discontinuity, requires prohibitively large memory to generate pulses with narrow widths and long periods and suffers from trigger uncertainty of up to one clock period when the pulse waveform is triggered by an external event. Moreover, it is not possible to modulate the width and delay of the pulse stored in the waveform memory. This paper describes a fully functional, low complexity, low cost, memory less, parallel and DDS based pulse waveform generator implemented in a low-cost field programmable gate arrays (FPGA) where pulse parameters such as amplitude, period, width, rise time, fall time and delay can all be varied without any glitches or phase discontinuity, where the amplitude, frequency and phase, as well as period, width and delay of the pulse can be modulated by an internally generated or external modulating signal and where it is possible to trigger the generation of the pulse or burst of pulses by an external event where the time between the trigger event and the pulse output is fixed.