This white paper gives an overview of digital modem technologies and how Xilinx high volume programmable devices can be used to implement complex system level glue in digital modem designs. The Xilinx device families targeted at these high volume applications include XC9500 CPLDs and Spartan FPGAs.

The flow of this document will start with an overview of the various digital modem technologies and how the factors driving their deployment. We will next examine the major functional blocks of a digital modem and give an overview of the Application Specific Standard Products (ASSPs) that are used in each functional block. We will then illustrate the system level glue functions that are needed in several different digital modem configurations.

While this document focuses on applications of these devices in digital modem applications, the examples discussed illustrate many of the issues found in other designs; specifically, how to cost effectively interface complex ASSPs with incompatible interfaces. The ASIC vendors have abandoned the traditional solution for this class of problems, the small ASIC, as they moved towards the system on chip market. Fortunately for system designers, new classes of low cost PLDs such as the Spartan family have filled this void with devices that replace low density ASICs and retain the time to market advantages of FPGAs.