SUPERCONDUCTING DIRECT DIGITAL SYNTHESIZER

Communications transmitters, receivers, radar applications, acid relat ed test equipment require precise control overgenerated frequencies wh ich can be provided by digital synthesist Superconductivity technology offers to greatly improve the operational frequency range at a tiny f raction of the power of present GaAs and Si digital frequency synthesi zers, an important consideration for systems with multiple receiver el ements and satellite applications. We designed, fabricated, and tested a digital superconducting frequency synthesizer an a 1-cm square subs trate in niobium technology and tested at 4 Kelvin. The chip contains a 12-bit pipelined MVTL incremental phase accumulator (simple expansio n to 32 bits achieves one part in 4.3 x 10(9) frequency resolution). T he most significant 10-bits of the accumulated phase proceed to a Sine ROM which is based on SQUlD cells and employs data compression to min imize circuit size. An 8-bit ROM output word proceeds to a superconduc ting D/A converter to construct the analog output waveform which updat es each clock cycle. We have operated the entire superconducting synth esizer above 1 GHz. Our performance goal with present fabrication tech nology is greater than or equal to 4 GHz operation.