Design of SFQ-counting analog-to-digital converter

We describe the design of an oversampling single-flux-counting analog-to-digital converter with the estimated bandwidth of a few tens of MHz, based on Rapid Single-Flux-Quantum (RSFQ) devices. It consists of an input analog circuit, high-speed quantizer with an original analog/digital negative feedback loop, decimation (comb) filter, and supporting subsystems including clock distribution circuits, quantization signal conditioner, and output drivers. We have applied a new approach, the 'symmetrizing' negative feedback, to free the quantizer from the intrinsic hysteresis without dynamic range sacrifice. The 16-bit version of the system comprises about 1,500 Josephson junctions and consumes 1.2 mW of DC power, when implemented using Nb-trilayer technology with 1 kA/cm/sup 2/, 3.5 /spl mu/m Josephson junctions. All subsystems of the converter have been successfully tested and testing of the system as a whole is in progress.<
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