A NEW DIGITAL MODULATION TECHNOLOGY

Direct digital modulation for hardware-in-the-loop simulations of airborne radar systems is currently digital multiplier limited. A digital multiplier technology which can support 8-bit modulation rates of at least 250 MHz with a maximun incurred signal delay of 100 nanoseconds is required. To achieve bandwidths required of the RF modulation, a massive array of state-of-the-art conventional digital multipliers would be required. The Athena solution is based on an alternative numeric representation known as the residue number system or RNS. Arithmetic is partitioned into simple, "narrow" channels which operate at a high speed. Our particular implementation of the RNS can perform a multiplication with just one real addition! Our Phase I research will denonstrate that it is possible to build a modulator which supports RF modulation using only a few channels consisting of eight-bit adders! In GaAs, this translates into a multiplication throughput of nearly 1 GHz. We will show that we can perform number system conversions with limited overhead and only a slight penalty in latency (far, far less than the prescribed 100 nanoseconds maximun). Furthermore, the timing requirement of our RNS design is minimal. The designs are highly pipelined, with only local data communication and a single clock. The technology will bedemonstrated using discrete components. A custom VLSI layout of the design will also be completed.