Programmable logic based current control of light emitting diodes using sigma-delta modulation

In this paper, the design and operation of a sigma-delta modulation based signal generator for the creation of signal waveforms to be used in current mode control of light emitting diodes (LEDs) is presented. The LED is to be used as the light source within an optical fiber sensor (OFS) system and is to be driven with known current waveforms for use within the system. In this paper, the use of pulse density modulation (PDM) is considered and waveforms are generated using a MATLAB/Simulink model of the analog waveform to encode along with a model of the sigma-delta modulator used. The output from the MATLAB/Simulink model is a sigma-delta encoded bit stream along with a VHDL design description that implements the signal in digital memory that can be synthesized into logic to target a suitable programmable logic device (PLD).