Analogue demonstration of a high temperature superconducting sigma-delta modulator with 27 GHz sampling

We have successfully fabricated and tested a high temperature superconducti ng (HTS) sigma-delta modulator for analogue-to-digital conversion. This is the first demonstration of a GHz sampling A-to-D in HTS. The 15-junction si ngle-flux-quantum (SFQ) circuit, fabricated using an epitaxial multilayer H TS process with YBCO/Co-YBCO/YBCO edge junctions, was internally clocked at 27 GHz and used to convert a 5.01 MHz signal. The modulator demonstrated a spur-free dynamic range of more than 75 dB. Two-tone measurements with 5.0 1 MHz and 5.51 MHz signals demonstrated third-order intermodulation product s to be lower than -59 dBc. Demonstration of a functional HTS modulator rep resents a significant milestone in the development of high dynamic range AD Cs suitable for such applications as surveillance radar.