Teaching Rate Conversion using Hardware-Based DSP

To enable us to affordably teach software defined radio at the undergraduate level, we developed a low cost system that allows realistic hardware projects and demonstrations. This new board connects a Texas Instruments C67x DSP starter kit (DSK) to an analog devices AD9857 quadrature modulator. This modulator is capable of operating at up to 200 million samples per second (MS/s), with a carrier (or intermediate frequency) of up to 80 MHz. Baseband 14-bit in-phase and quadrature (I/Q) data are presented to the modulator, which can be programmed to interpolate the data at rates from 4x to 252x. The AD9857 is interfaced to the DSK using an Altera Cyclone FPGA which provides queuing of the I/Q data and the logic for control/programming of the modulator. This paper describes the associated hardware and software issues and briefly describes recommended classroom use.