Computer interfacing and analysis of a sigma-delta analog-to-digital converter

The suitability of a 16 bit Motorola DSP56ADC18 sigma-delta modulator analog to digital converter for use in audio and instrumentation applications was studied using statistical and Fourier analysis. In addition, a personal computer interface was developed that was quite reliable, yet reasonably priced and is practical for home use. Such a device was designed for use externally to the PC parallel port and built to allow data from the A/D to be stored in computer memory. Driver software was written using C and assembly language to interact with the external hardware and to manage the data flow from the A/D. Hardware and software were optimized to take full advantage of the sampling speed of the A/D. The DC stability of the A/D was compared to the manufacturer's specifications by statistical methods using data obtained by sampling the voltage level of a battery over various time intervals. Dynamic performance was demonstrated by sampling known signals and creating plots of the sampled data as well as plots of the FFT analysis. The performance of the A/D combined with the PC interface circuit was found to have very good DC stability and excellent response to audio band signals. Sample rates as high as 93,750 samples per second were achieved using an Intel Pentium processor running at 60 MHz. The DC stability proved to be within the manufacturer's specified limits.