Superconducting direct digital synthesizer

Communications transmitters, receivers, radar applications, and related test equipment require precise control over generated frequencies which can be provided by digital synthesis. Superconductivity technology offers to greatly improve the operational frequency range at a tiny fraction of the power of present GaAs and Si digital frequency synthesizers, an important consideration for systems with multiple receiver elements and satellite applications. We designed, fabricated, and tested a digital superconducting frequency synthesizer on a 1-cm square substrate in niobium technology and tested at 4 Kelvin. The chip contains a 12-bit pipelined MVTL incremental phase accumulator (simple expansion to 32 bits achieves one part in 4.3/spl times/10/sup 9/ frequency resolution). The most significant 10-bits of the accumulated phase proceed to a Sine ROM which is based on SQUID cells and employs data compression to minimize circuit size. An 8-bit ROM output word proceeds to a superconducting D/A converter to construct the analog output waveform which updates each clock cycle. We have operated the entire superconducting synthesizer above 1 GHz. Our performance goal with present fabrication technology is /spl ges/4 GHz operation.