Design and Evaluation of 2-bit-Input Single-Flux-Quantum Autocorrelator System for Astronomical Data Analysis

To improve the accuracy of astronomical data analysis, an increase in the number of output bits from the A/D converter is effective. We investigated a single-flux-quantum (SFQ) autocorrelator and an integrator that supports multiple-bit signal output from an SFQ A/D converter for astronomical data processing. The SFQ binary counter was used as the integrator that decimates the output from the SFQ autocorrelator for communication with equipment at room temperature. We designed the test circuits composed of 2-bit inputs, an autocorrelator, and an integrator that contains 5631 Josephson junctions using the 10 kA/cm
²
Nb process. We confirmed the correct operation of the test circuit with a normalized bias voltage margin of 102%-114% by the low-speed test. We obtained its correct high-speed operation up to a 55.1 GHz clock frequency. In terms of circuit design, scaling up the test circuit is easy. These results indicate the effectiveness of a high-precision and large-bandwidth radio astronomical observation using SFQ circuit technology.